This study was supported by the National Key Research and Development Program of China (2018YFA0901500), the National Key Scientific Instrument and Equipment Project of the National Natural Science Foundation of China (21627812), and the Tsinghua University Initiative Scientific Research Program (20161080108). We also thank Prof. Julia A. Vorholt (Institute of Microbiology, Department of Biology, ETH Zurich, Zurich 8093, Switzerland) for the provision of the methanol-essential E. coli strain version 2.2 (MeSV2.2).

1. Instrument and software installation
<ol>
	<li>Choose a clean and sterile environment (such as a clean bench) as a dedicated permanent space for MMC. Install the MMC steadily in the space. 
	NOTE: Keep the MMC away from the interference of strong electric fields, magnetic fields, and strong heat radiation sources. Avoid severe vibration from affecting the optical detection components. Provide the power supply of AC220 V, 50 HZ to the MMC. For details on MMC refer to the Table of Materials and the website for MMC16.</li>
	<li>Install the operation software from the MMC.zip file 
	NOTE: Contact the authors for the MMC.zip file.
	<ol>
		<li>Create a dedicated folder and save the zip file in it.</li>
		<li>Create another dedicated folder as the &#34;Installation Directory&#34;. Unzip the MMC.zip and save the files in the new folder. 
		NOTE: The computer configuration is best to meet: (1) Windows 7 64-bit operating system or above; (2) CPU: i5 or above; (3) memory: 4 GB or above; (4) hard disk: 300 GB or above (rotational speed greater than 7200 rpm or solid-state disk).</li>
	</ol>
	</li>
</ol>
2. Preparations
<ol>
	<li>Connect the syringe needle (inner diameter is 0.41 mm and outer diameter is 0.71 mm), quick connector A, and reagent bottle (Figure 2C), and autoclave them at 121 &#176;C for 15 min. 
	NOTE: Unscrew the cap of the reagent bottle slightly during sterilization. A few more reagent bottles can be prepared each time for use.</li>
	<li>Use a 0.22 &#181;m polyvinylidene fluoride (PVDF) filter to filter MMC oil. Put the microfluidic chip (Figure 2B) and MMC oil into the clean bench in advance and sterilize them by ultraviolet irradiation for 30 min before use. 
	NOTE: For the details of Quick connector A, reagent bottle, MMC oil and microfluidic chip refer to the Table of Materials.</li>
	<li>Install the microfluidic chip
	<ol>
		<li>Open the door of the operation chamber (Figure 2A) and lift the optical fiber probe.</li>
		<li>Align the electric field holes with the electric field needles and gently place the chip on the chip pedestal. Then insert the two positioning columns into the positioning holes and put down the optical fiber probe (Figure 2D).</li>
		<li>Connect the quick connector A on the chip to the corresponding port of the MMC according to the position number (C5-O5, C4-O4, C6-O6, C2-O2, CF-OF, C1-O1, C3-O3). Then close the door of the operation chamber.</li>
	</ol>
	</li>
	<li>Replenish the MMC oil (to about 80 mL) in the oil bottle and empty the waste liquid in the waste bottle before use. 
	NOTE: The waste liquid is usually organic waste. Please refer to regional law and regulation upon disposal, subject to change based on experimental setup.</li>
</ol>
3.&#160;Growth curve measurement in MMC
<ol>
	<li>Preparation for initial bacterial solution
	<ol>
		<li>Follow the related standard regulations to prepare Luria-Bertani (LB) medium and autoclave at 121&#176;C for 15 min. 
		NOTE: Components of LB medium: NaCl (10 g/L), yeast extract (5 g/L) and tryptone (10 g/L).</li>
		<li>Take out the E. coli MG1655 strain from glycerol stock and cultivate it in a 50 mL shake flask with 10 mL of LB medium in a shaking incubator (200 rpm) at 37 &#176;C for 5-8 h. 
		NOTE: The cultivation time depends on the specific strains. It is optimal to cultivate the strain to the logarithmic period/phase.</li>
		<li>Dilute the cultured E. coli MG1655 solution with fresh medium to an OD600&#160;of 0.05-0.1 to obtain an initial bacteria solution (prepare about 10 mL).</li>
	</ol>
	</li>
	<li>Click on Initialization to initialize the MMC. After the initialization interface appears, set the cultivation temperature as 37 &#176;C and the photoelectric signal value as 0.6 (Figure 3A). Initialization will take about 20 min.</li>
	<li>Turn on the UV lamp (wavelength 254 nm) during initialization.</li>
	<li>Inject the initial bacteria solution and MMC oil into the reagent bottle.
	<ol>
		<li>Take out a sterilized reagent bottle on the clean bench and tighten the cap.</li>
		<li>Use a 10 mL sterile syringe to inject 3-5 mL of MMC oil from the syringe needle of the side tube. Tilt and rotate the reagent bottle slowly to make the oil fully infiltrate the inner wall.</li>
		<li>Inject about 5 mL of initial bacteria solution, and then fill the reagent bottle by injecting 5-7 mL of the oil again.</li>
		<li>Pull out the independent quick connector A, and insert the quick connector A of the reagent bottle into its quick connector B to complete the sample injection operation (Figure 4A).</li>
	</ol>
	</li>
	<li>Wait for the initialization to end and then turn off the UV lamp (wavelength 254 nm).</li>
	<li>Open the door of the operation chamber, and put the reagent bottle into the metal bath.</li>
	<li>Pull out the C2 connector of the chip and the quick connector A of the reagent bottle. Connect the side tube connector of the reagent bottle to the C2 connector and the top tube connector to the O2 connector. Then close the door of the operation chamber.</li>
	<li>Click on Growth Curve to choose the function of growth curve measurement (Figure 3A). In the parameter setting interface, input the Number as 15, turn on the OD detection switch and set the Wavelength as 600 nm. Click on Start to start droplet generation. It will take about 10 min. 
	NOTE: Here, Number refers to the number of droplets to be generated. Wavelength refers to the wavelength of the OD to be detected. Set the Number (maximum 200) and Wavelength (350-800 nm) according to the experiment requirements.</li>
	<li>When a pop-up window appears on the main interface prompting &#34;Remove the reagent bottle between C2 and O2, then please click the OK button after completion&#34;, open the door of the operation chamber to take out the reagent bottle and connect the C2 and O2 connectors.</li>
	<li>Close the door, and click the OK button in the pop-up window to automatically cultivate the droplets and detect the OD values. 
	NOTE: The MMC detects the OD value when the droplet passes the optical fiber probe. Therefore, the detection period depends on the number of droplets generated.</li>
	<li>When the growth curve reaches the stationary phase, click the Data Export button to export the OD data. Select the data save path and export the OD value recorded during the cultivation period in the .csv format, which can be opened by appropriate software (e.g., Microsoft Excel). Then use a mapping software (e.g., EXCEL and Origin 9.0) to plot the growth curve. 
	NOTE: During the cultivation process, it is feasible to click on the Data Export at any time to export the OD data of all the current droplets.</li>
</ol>
4. Adaptive evolution in MMC
<ol>
	<li>Preparation for initial bacterial solution
	<ol>
		<li>Follow the related standard regulations to prepare the special liquid medium and solid plates for the MeSV2.2 and autoclave at 121 &#176;C for 15 min. 
		NOTE: For the components of the special medium refer to Table 1&#160;and the Table of Materials.</li>
		<li>Cultivate the MeSV2.2 using the solid plate (diameter = 90 mm) in a 37 &#176;C constant temperature incubator for 72 h. Then pick an independent colony and cultivate it in a 50 mL shake flask with 10 mL of the special liquid medium in a shaking incubator (200 rpm) at 37 &#176;C for 72 h.</li>
		<li>Dilute the cultured MeSV2.2 solution with the medium to an OD600&#160;of 0.1-0.2 (ensure that the total volume is not less than 10 mL) and continue cultivating it in the shake flask for 5 h to obtain the initial bacteria solution. 
		NOTE: The MeSV2.2 is a methanol-essential E. coli strain. The special liquid medium contains 500 mmol/L methanol, which is a strong stress for MeSV2.2, resulting in very slow growth. Note that obtaining the initial bacteria solution here is different from that described in step 3.1.</li>
	</ol>
	</li>
	<li>Initialize the MMC as explained in steps 3.2, 3.3, and 3.5.</li>
	<li>Take out two sterilized reagent bottles, one of which is for the initial bacteria solution and the other is for the fresh medium. Inject the initial bacteria solution (5 mL), fresh medium (12-15 mL), and MMC oil into the reagent bottles as explained in step 3.4. 
	NOTE: As adaptive evolution is a long-term process involving multiple sub-cultivations, store as much fresh medium as possible in MMC. The medium cannot be replenished during the experiment running.</li>
	<li>Install the two reagent bottles into MMC as explained in step 3.6. Install the one for the initial bacteria solution between the C2 and O2 connector and the other for the fresh medium between the C4 and O4 connector.</li>
	<li>Click on ALE to choose the function of adaptive evolution (Figure 3B). In the parameter setting interface, turn on the OD Detection switch.</li>
	<li>Set the Number as 50, Wavelength as 600 nm, Concentration as 0%, Type as Time, Parameter as 30 h, and Repetitions as 99. Click on Start to start droplet generation. It will take about 25 min. 
	NOTE: Here, &#34;Concentration&#34; refers to the maximum concentration of chemical factors for adaptive evolution. For different droplets, it is realizable in MMC to introduce different concentrations of chemical factors to provide different growth conditions. Calculate the introduced concentrations using the following equation: 
	<img alt="Equation 1" src="/files/ftp_upload/62800/62800eq01.jpg" /> 
	Here &#34;C&#34; refers to the concentration of chemical factors introduced into droplets; &#34;a&#34; refers to the concentration of chemical factors in the reagent bottles between the C4 and O4 connector; &#34;b&#34; refers to the concentration of chemical factors in the reagent bottles between the C6 and O6 connector; and &#34;i&#34; refers to the available concentration. There are eight concentrations available in MMC. Since the chemical factor here has a single concentration (500 mmol/L methanol) and it is one of the ingredients of the medium, only one reagent bottle containing the chemical factor is installed here, and the Concentration is set as 0%. Type refers to the mode of sub-cultivation, which is divided into three types: time mode, OD value mode, and fluorescence mode. The former means to cultivate the droplets for a fixed time and then sub-cultivate, while the latter two means to cultivate the droplets to pre-defined OD value/fluorescence intensity and then sub-cultivate. Parameter refers to the related parameter required when choosing a mode of sub-cultivation. Repetitions refers to the number of sub-cultivations.</li>
	<li>Remove the reagent bottle placed between the C2 and O2 connector as explained in step 3.8.</li>
	<li>Observe whether the maximum OD values of the droplets during each sub-cultivation period have increased significantly. If the increase occurs and meets the experiment requirements, click on the Data Export button to export the OD data as explained in step 3.9. 
	NOTE: Here, the sub-cultivation period depends on&#160;the Parameter. For example, when setting Type as Time and Parameter as 30 h, the sub-cultivation period is 30 h. During each sub-cultivation period, there are the maximum OD values of the droplets. Estimate whether the adaptive evolution meets the experiment requirements by the increase of maximum OD values (The increase depends on the actual cultivation process of the strain, for example, increased by more than 20%). 
	CAUTION: Pay attention to whether the stored fresh medium is exhausted. If the significant increase has not occurred even after the medium is exhausted, extract the better-growing droplets and carry out a new round of adaptive evolution.</li>
	<li>Extract the target droplets from the MMC.
	<ol>
		<li>Click on the Screening button to choose the function of droplet extraction (Figure 3C). Choose the Collect option, click on the numbers of target droplets, and then click on OK. 
		NOTE: Droplet screening includes &#34;Collect&#34;, &#34;Discard&#34; and &#34;Extract seed solution&#34;. &#34;Extract seed solution&#34; means to collect the remaining droplets13&#160;after the sub-cultivation operation.</li>
		<li>Wait for the pop-up window to prompt, &#34;Please pull out the CF quick connector and put it into the EP tube&#34;. Put the CF quick connector into the microcentrifuge tube for collection according to the software prompt and then click on OK (Figure 4D).</li>
		<li>After 1-2 min, the software interface will pop up a new window prompting, &#34;Please insert the connector back and click OK if finished&#34;. Then, insert the CF quick connector back and click on OK to make MMC continue to run (Figure 4D). When the next target droplet reaches the droplet recognition site, repeat 4.9.2-4.9.3 to collect it. 
		NOTE: After all the target droplets are collected, the MMC will continue cultivating the remaining droplets. If the cultivation is not necessary, click on Stop to directly terminate the operation.</li>
		<li>Extract the droplet using a 2.5 &#181;L pipette, drop it on the 90 mm agarose plate, and spread it evenly with a triangular glass&#160;spreading rod with a side length of 3 cm. Then cultivate it in a 37 &#176;C constant temperature incubator for 72 h.</li>
		<li>Pick 3-5 independent colonies and separately cultivate them in the 50 mL shake flasks with 10 mL of fresh medium in a shaking incubator (200 rpm) at 37 &#176;C for 48-72 h. Follow the related standard regulations to store the cultured bacteria solution in the glycerol tube for subsequent experiments.</li>
	</ol>
	</li>
</ol>
5. Clean of the MMC
<ol>
	<li>After completion of the experiment, click on Stop to stop all the operations. Then click on Clean to clean the chip and tubes. It will take about 15 min.</li>
</ol>

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The authors have nothing to disclose.

This protocol presents how to use the Microbial Microdroplet Culture system (MMC) to perform automated microbial cultivation and long-term adaptive evolution. MMC is a miniaturized, automated, and high-throughput microbial cultivation system. Compared with conventional microbial high-throughput cultivation methods and instruments, MMC has many advantages such as low labor and reagent consumption, simple operation, online detection (OD and fluorescence), high-time-resolution data collection, and superior parallelization. ...

Microbial cultivation is an important foundation for microbiological scientific research and industrial applications, which is widely used in the isolation, identification, reconstruction, screening, and evolution of microorganisms1,2,3. Conventional microbial cultivation methods mainly use test tubes, shake flasks, and solid plates as cultivation containers, combined with shaking incubators, spectrophotometers, microplate readers, and other equipment for microbial cultivation, detection, and screening. However, these methods have many problems, such as cumbersome operations, low throughput, low efficiency, and large consumption of labor and reagents. The high-throughput cultivation methods developed in recent years are mainly based on the microplate. But the microplate has a low level of dissolved oxygen, poor mixing property, and severe evaporation and thermal effect, which often lead to poor growth status and experiment parallelization of microorganisms4,5,6,7; on the other hand, it needs to be equipped with expensive equipment, such as liquid-handling workstations and microplate readers, to achieve automated cultivation and process detection8,9.
As an important branch of microfluidic technology, droplet microfluidics has been developed in recent years based on traditional continuous-flow microfluidic systems. It is a discrete flow microfluidic technology that uses two immiscible liquid phases (usually oil-water) to generate dispersed micro-droplets and operate on them10. Because micro-droplets have the characteristics of small volume, large specific surface area, high internal mass transfer rate, and no cross-contamination caused by compartmentalization, and the advantages of strong controllability and high throughput of droplets, there have been many kinds of research applying droplet microfluidic technology in high-throughput cultivation, screening, and evolution of microorganisms11. However, there are still a series of key issues to make droplet microfluidic technology popularized and widely applied. Firstly, the operation of droplet microfluidics is cumbersome and intricate, resulting in high technical requirements for operators. Secondly, droplet microfluidic technology combines optical, mechanical, and electrical components and needs to be associated with biotechnology application scenarios. It is difficult for a single laboratory or team to build efficient droplet microfluidic control systems if there is no multi-disciplinary collaboration. Thirdly, on account of the small volume of micro-droplet (from picoliter (pL) to microliter (&#956;L)), it takes much difficulty to realize the precise automated control and real-time online detection of droplets for some basic microbial operations such as sub-cultivation, sorting, and sampling, and it is also difficult to construct an integrated equipment system12.
In order to address the above problems, an automatic Microbial Microdroplet Culture system (MMC) was successfully developed based on droplet microfluidic technology13. The MMC consists of four functional modules: a droplet recognition module, a droplet spectrum detection module, a microfluidic chip module, and a sampling module. Through the system integration and control of all the modules, automated operation system including the generation, cultivation, measurement (optical density (OD) and fluorescence), splitting, fusion, sorting of droplets is accurately established, achieving the integration of functions such as inoculation, cultivation, monitoring, sub-cultivation, sorting and sampling required by the process of microbial droplet cultivation. MMC can hold up to 200 replicate droplet cultivation units of 2-3 &#181;L volume, which is equivalent to 200 shake flask cultivation units. The micro-droplet cultivation system can satisfy the requirements of non-contamination, dissolved oxygen, mixing, and mass-energy exchange during the growth of microorganisms, and meet the various needs of microbial research through multiple integrated functions, for instance, growth curve measurement, adaptive evolution, single factor multi-level analysis, and metabolite research and analysis (based on fluorescence detection)13,14.
Here, the protocol introduces how to use the MMC to conduct automated and microbial cultivation and adaptive evolution in detail (Figure 1). We took wild-type Escherichia coli (E. coli) MG1655 as an example to demonstrate the growth curve measurement and a methanol-essential E. coli strain MeSV2.215&#160;to demonstrate the adaptive evolution in MMC. An operation software for MMC was developed, which makes the operation very simple and clear. In the whole process, the user needs to prepare the initial bacteria solution, set the conditions of the MMC, and then inject the bacteria solution and related reagents into the MMC. Subsequently, the MMC will automatically perform operations such as droplet generation, recognition and numbering, cultivation, and adaptive evolution. It also will perform online detection (OD and fluorescence) of the droplets with high time resolution and display the related data (which can be exported) in the software. The operator can stop the cultivation process at any time according to the results and extract the target droplets for subsequent experiments. The MMC is easy to operate, consumes less labor and reagents, and has relatively high experimental throughput and good data parallelity, which has significant advantages compared with conventional cultivation methods. It provides a low-cost, operation-friendly, and robust experimental platform for researchers to conduct related microbial research.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0.22 &#956;m PVDF filter membrane</td>
			<td>Merck Millipore Ltd.</td>
			<td>SLGPR33RB</td>
			<td>Sterilize the MMC oil</td>
		</tr>
		<tr>
			<td>4 &#176;C refrigerator</td>
			<td>Haier</td>
			<td>BCD-289BSW</td>
			<td>For reagent storage</td>
		</tr>
		<tr>
			<td>Agar</td>
			<td>Becton, Dickinson and Company</td>
			<td>214010</td>
			<td>For solid plate preparation</td>
		</tr>
		<tr>
			<td>CaCl2&#183;2H2O</td>
			<td>Sinopharm Chemical Reagent Beijing Co., Ltd.</td>
			<td>20011160</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
		<tr>
			<td>Clean bench</td>
			<td>Beijing Donglian Har Instrument Manufacture Co., Ltd.</td>
			<td>DL-CJ-INDII</td>
			<td>For aseptic operation and UV sterilization</td>
		</tr>
		<tr>
			<td>CoCl2&#183;6H2O</td>
			<td>Sinopharm Chemical Reagent Beijing Co., Ltd.</td>
			<td>10007216</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
		<tr>
			<td>Computer</td>
			<td>Lenovo</td>
			<td>E450</td>
			<td>Software installation and MMC control</td>
		</tr>
		<tr>
			<td>Constant temperature incubator</td>
			<td>Shanghai qixin scientific instrument co., LTD</td>
			<td>LRH 250</td>
			<td>For the microbial cultivation using solid medium</td>
		</tr>
		<tr>
			<td>CuSO4&#183;5H2O</td>
			<td>Sinopharm Chemical Reagent Beijing Co., Ltd.</td>
			<td>10008218</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
		<tr>
			<td>Electronic balance</td>
			<td>OHAUS</td>
			<td>AR 3130</td>
			<td>For reagent weighing</td>
		</tr>
		<tr>
			<td>EP tube</td>
			<td>Thermo Fisher</td>
			<td>1.5 mL</td>
			<td>For droplet collection</td>
		</tr>
		<tr>
			<td>FeCl3&#183;6H2O</td>
			<td>Sinopharm Chemical Reagent Beijing Co., Ltd.</td>
			<td>10011928</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
		<tr>
			<td>Freezing Tube</td>
			<td>Thermo Fisher</td>
			<td>2.0 mL</td>
			<td>For strain preservation</td>
		</tr>
		<tr>
			<td>Gluconate</td>
			<td>Sigma-Aldrich</td>
			<td>S2054</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>GENERAL-REAGENT</td>
			<td>G66258A</td>
			<td>For strain preservation</td>
		</tr>
		<tr>
			<td>High-Pressure Steam Sterilization Pot</td>
			<td>SANYO Electric</td>
			<td>MLS3020</td>
			<td>For autoclaved sterilization</td>
		</tr>
		<tr>
			<td>isopropyl-&#946;-d-thiogalactopyranoside (IPTG)</td>
			<td>Biotopped</td>
			<td>420322</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
		<tr>
			<td>Kanamycin sulfate</td>
			<td>Solarbio</td>
			<td>K8020</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>MACKLIN</td>
			<td>P815661</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>MACKLIN</td>
			<td>M813895</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
		<tr>
			<td>MgSO4&#183;7H2O</td>
			<td>BIOBYING</td>
			<td>1305715</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
		<tr>
			<td>Microbial Microdroplet Culture System (MMC)</td>
			<td>Luoyang TMAXTREE Biotechnology Co., Ltd.</td>
			<td>&#160;MMC-I</td>
			<td>Performing growth curve determination and adaptive evolution. Please refer to http://www.tmaxtree.com/en/index.php?v=news&#38;id=110</td>
		</tr>
		<tr>
			<td>Microfluidic chip</td>
			<td>Luoyang TMAXTREE Biotechnology Co., Ltd.</td>
			<td>MMC-ALE-OD</td>
			<td>For various droplet operations. Please refer to http://www.tmaxtree.com/en/</td>
		</tr>
		<tr>
			<td>MMC oil</td>
			<td>Luoyang TMAXTREE Biotechnology Co., Ltd.</td>
			<td>MMC-M/S-OD</td>
			<td>The oil phase for droplet microfluidics. Please refer to http://www.tmaxtree.com/en/</td>
		</tr>
		<tr>
			<td>MnCl2</td>
			<td>Sinopharm Chemical Reagent Beijing Co., Ltd.</td>
			<td>20026118</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>GENERAL-REAGENT</td>
			<td>G81793J</td>
			<td>Component of the LB medium</td>
		</tr>
		<tr>
			<td>Na2HPO4&#183;12H2O</td>
			<td>GENERAL-REAGENT</td>
			<td>G10267B</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
		<tr>
			<td>NH4Cl</td>
			<td>Sinopharm Chemical Reagent Beijing Co., Ltd.</td>
			<td>10001518</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
		<tr>
			<td>Petri dish</td>
			<td>Corning Incorporated</td>
			<td>90 mm</td>
			<td>For the preparation of solid medium</td>
		</tr>
		<tr>
			<td>Pipette</td>
			<td>eppendorf</td>
			<td>2.5 &#956;L, 10 &#956;L, 100&#956;L, 1000&#956;L</td>
			<td>For liquid handling</td>
		</tr>
		<tr>
			<td>Quick connector A</td>
			<td>Luoyang TMAXTREE Biotechnology Co., Ltd.</td>
			<td>&#8212;</td>
			<td>For the connection of each joint. Please refer to http://www.tmaxtree.com/en/</td>
		</tr>
		<tr>
			<td>Reagent bottle</td>
			<td>Luoyang TMAXTREE Biotechnology Co., Ltd.</td>
			<td>MMC-PCB</td>
			<td>Sampling and storage of bacteria solution and reagents. Please refer to http://www.tmaxtree.com/en/</td>
		</tr>
		<tr>
			<td>Shake flask</td>
			<td>Union-Biotech</td>
			<td>50 mL</td>
			<td>For microbial cultivation</td>
		</tr>
		<tr>
			<td>Shaking incubator</td>
			<td>Shanghai Sukun Industrial Co., Ltd.</td>
			<td>SKY-210 2B</td>
			<td>For the microbial cultivation in shake flask</td>
		</tr>
		<tr>
			<td>Streptomycin sulfate</td>
			<td>Solarbio</td>
			<td>S8290</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
		<tr>
			<td>Syringe</td>
			<td>JIANGSU ZHIYU MEDICAL INSTRUCTMENT CO., LTD</td>
			<td>10 mL</td>
			<td>Draw liquid and inject it into the reagent bottle</td>
		</tr>
		<tr>
			<td>Syringe needle</td>
			<td>OUBEL Hardware Store</td>
			<td>22G</td>
			<td>Inner diameter is 0.41 mm and outer diameter is 0.71 mm.</td>
		</tr>
		<tr>
			<td>Tryptone</td>
			<td>Oxoid Ltd.</td>
			<td>LP0042</td>
			<td>Component of the LB medium</td>
		</tr>
		<tr>
			<td>Ultra low temperature refrigerator</td>
			<td>SANYO Ultra-low</td>
			<td>MDF-U4086S</td>
			<td>For strain preservation (-80 &#176;C)</td>
		</tr>
		<tr>
			<td>UV&#8211;Vis spectrophotometer</td>
			<td>General Electric Company</td>
			<td>Ultrospec 3100 pro</td>
			<td>For the measurement of OD values</td>
		</tr>
		<tr>
			<td>Vitamin B1</td>
			<td>Solarbio</td>
			<td>SV8080</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
		<tr>
			<td>Yeast extract</td>
			<td>Oxoid Ltd.</td>
			<td>LP0021</td>
			<td>Component of the LB medium</td>
		</tr>
		<tr>
			<td>ZnSO4&#183;7H2O</td>
			<td>Sinopharm Chemical Reagent Beijing Co., Ltd.</td>
			<td>10024018</td>
			<td>Component of the special medium for MeSV2.2.</td>
		</tr>
	</tbody>
</table>

automated microbial cultivation and adaptive evolution using microbial microdroplet culture system (mmc)

Conventional microbial cultivation methods usually have cumbersome operations, low throughput, low efficiency, and large consumption of labor and reagents. Moreover, microplate-based high-throughput cultivation methods developed in recent years have poor microbial growth status and experiment parallelization because of their low dissolved oxygen, poor mixture, and severe evaporation and thermal effect. Due to many advantages of micro-droplets, such as small volume, high throughput, and strong controllability, the droplet-based microfluidic technology can overcome these problems, which has been used in many kinds of research of high-throughput microbial cultivation, screening, and evolution. However, most prior studies remain&#160;at the stage of laboratory construction and application. Some key issues, such as high operational requirements, high construction difficulty, and lack of automated integration technology, restrict the wide application of droplet microfluidic technology in microbial research. Here, an automated Microbial Microdroplet Culture system (MMC) was successfully developed based on droplet microfluidic technology, achieving the integration of functions such as inoculation, cultivation, online monitoring, sub-cultivation, sorting, and sampling required by the process of microbial droplet cultivation. In this protocol, wild-type Escherichia coli (E. coli) MG1655 and a methanol-essential E. coli strain (MeSV2.2) were taken as examples to introduce how to use the MMC to conduct automated and relatively high-throughput microbial cultivation and adaptive evolution in detail. This method is easy to operate, consumes less labor and reagents, and has high experimental throughput and good data parallelity, which has great advantages compared with conventional cultivation methods. It provides a low-cost, operation-friendly, and result-reliable experimental platform for scientific researchers to conduct related microbial research.

This protocol uses E. coli MG1655 and a MeSV2.2 strain as examples to demonstrate the microbial cultivation and methanol-essential adaptive evolution with an automated and relatively high-throughputstrategy in MMC. The growth curve measurement was mainly used to characterize microbial cultivation. The adaptive evolution was conducted by automated continuous sub-cultivation and adding a high concentration of methanol as the selective pressure during each sub-cultivation. Whether adaptive evolution had been realiz...

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Automated Microbial Cultivation and Adaptive Evolution using Microbial Microdroplet Culture System MMC

This protocol describes how to use the Microbial Microdroplet Culture system (MMC) to conduct automated microbial cultivation and adaptive evolution. MMC can cultivate and sub-cultivate microorganisms automatically and continuously and monitor online their growth with relatively high throughput and good parallelization, reducing labor and reagent consumption.

Automated Microbial Cultivation and Adaptive Evolution using Microbial Microdroplet Culture System (MMC)

Conventional microbial cultivation methods usually have cumbersome operations, low throughput, low efficiency, and large consumption of labor and ...

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3.5K Views.  Tsinghua University. This protocol describes how to use the Microbial Microdroplet Culture system (MMC) to conduct automated microbial cultivation and adaptive evolution. MMC can cultivate and sub-cultivate microorganisms automatically and continuously and monitor online their growth with relatively high throughput and good parallelization, reducing labor and reagent consumption.

Video: Automated Microbial Cultivation and Adaptive Evolution using Microbial Microdroplet Culture System MMC

Microfluidic Picoliter Bioreactor for Microbial Single-cell Analysis: Fabrication, System Setup, and Operation

In this protocol the fabrication, experimental setup and basic operation of the recently introduced microfluidic picoliter bioreactor (PLBR) is described in detail. The PLBR can be utilized for the analysis of single bacteria and microcolonies to investigate biotechnological and microbiological related questions concerning, e.g.&#160;cell growth, morphology, stress response, and metabolite or protein production on single-cell level. The device features continuous media flow enabling constant environmental conditions for perturbation studies, but in addition allows fast medium changes as well as oscillating conditions to mimic any desired environmental situation. To fabricate the single use devices, a silicon wafer containing sub micrometer sized SU-8 structures served as the replication mold for rapid polydimethylsiloxane casting. Chips were cut, assembled, connected, and set up onto a high resolution and fully automated microscope suited for time-lapse imaging, a powerful tool for spatio-temporal cell analysis. Here, the biotechnological platform organism Corynebacterium glutamicum&#160;was seeded into the PLBR and cell growth and intracellular fluorescence were followed over several hours unraveling time dependent population heterogeneity on single-cell level, not possible with conventional analysis methods such as flow cytometry. Besides insights into device fabrication, furthermore, the preparation of the preculture, loading, trapping of bacteria, and the PLBR cultivation of single cells and colonies is demonstrated. These devices will add a new dimension in microbiological research to analyze time dependent phenomena of single bacteria under tight environmental control. Due to the simple and relatively short fabrication process the technology can be easily adapted at any microfluidics lab and simply tailored towards specific needs.

In this protocol the fabrication, setup and basic operation of a microfluidic picoliter bioreactor (PLBR) for single-cell analysis of prokaryotic microorganisms is introduced. Industrially relevant microorganisms were analyzed as proof of principle allowing insights into growth rate, morphology, and phenotypic heterogeneity over certain time periods, hardly possible with conventional methods.

In this protocol the fabrication, experimental setup and basic operation of the recently introduced microfluidic picoliter bioreactor (PLBR) is described ...

Synthesis of an Intein-mediated Artificial Protein Hydrogel

We present the synthesis of a highly stable protein hydrogel mediated by a split-intein-catalyzed protein trans-splicing reaction. The building blocks of this hydrogel are two protein block-copolymers each containing a subunit of a trimeric protein that serves as a crosslinker and one half of a split intein. A highly hydrophilic random coil is inserted into one of the block-copolymers for water retention. Mixing of the two protein block copolymers triggers an intein trans-splicing reaction, yielding a polypeptide unit with crosslinkers at either end that rapidly self-assembles into a hydrogel. This hydrogel is very stable under both acidic and basic conditions, at temperatures up to 50 &#176;C, and in organic solvents. The hydrogel rapidly reforms after shear-induced rupture. Incorporation of a &#34;docking station peptide&#34; into the hydrogel building block enables convenient incorporation of &#34;docking protein&#34;-tagged target proteins. The hydrogel is compatible with tissue culture growth media, supports the diffusion of 20 kDa molecules, and enables the immobilization of bioactive globular proteins. The application of the intein-mediated protein hydrogel as an organic-solvent-compatible biocatalyst was demonstrated by encapsulating the horseradish peroxidase enzyme and corroborating its activity.

We present the synthesis of a split-intein-mediated protein hydrogel. The building blocks of this hydrogel are two protein copolymers each containing a subunit of a trimeric protein that serves as a crosslinker and one half of a split intein. Mixing of the two protein copolymers triggers an intein trans-splicing reaction, yielding a polypeptide unit that self-assembles into a hydrogel. This hydrogel is highly pH- and temperature-stable, compatible with organic solvents, and easily incorporates functional globular proteins.

We present the synthesis of a highly stable protein hydrogel mediated by a split-intein-catalyzed protein trans-splicing reaction. The building blocks of ...

Cultivation of Mammalian Cells Using a Single-use Pneumatic Bioreactor System

Recent advances in mammalian, insect, and stem cell cultivation and scale-up have created tremendous opportunities for new therapeutics and personalized medicine innovations. However, translating these advances into therapeutic applications will require in vitro systems that allow for robust, flexible, and cost effective bioreactor systems. There are several bioreactor systems currently utilized in research and commercial settings; however, many of these systems are not optimal for establishing, expanding, and monitoring the growth of different cell types. The culture parameters most challenging to control in these systems include, minimizing hydrodynamic shear, preventing nutrient gradient formation, establishing uniform culture medium aeration, preventing microbial contamination, and monitoring and adjusting culture conditions in real-time. Using a pneumatic single-use bioreactor system, we demonstrate the assembly and operation of this novel bioreactor for mammalian cells grown on micro-carriers. This bioreactor system eliminates many of the challenges associated with currently available systems by minimizing hydrodynamic shear and nutrient gradient formation, and allowing for uniform culture medium aeration. Moreover, the bioreactor&#8217;s software allows for remote real-time monitoring and adjusting of the bioreactor run parameters. This bioreactor system also has tremendous potential for scale-up of adherent and suspension mammalian cells for production of a variety therapeutic proteins, monoclonal antibodies, stem cells, biosimilars, and vaccines.

Using a pneumatic bioreactor, we demonstrate the assembly, operation, and performance of this single-use bioreactor system for the growth of mammalian cells.

Recent advances in mammalian, insect, and stem cell cultivation and scale-up have created tremendous opportunities for new therapeutics and personalized ...

Electrotaxis Studies of Lung Cancer Cells using a Multichannel Dual-electric-field Microfluidic Chip

The behavior of directional cell migration under a direct current electric-field (dcEF) is referred to as electrotaxis. The significant role of physiological dcEF in guiding cell movement during embryo development, cell differentiation, and wound healing has been demonstrated in many studies. By applying microfluidic chips to an electrotaxis assay, the investigation process is shortened and experimental errors are minimized. In recent years, microfluidic devices made of polymeric substances (e.g., polymethylmethacrylate, PMMA, or acrylic) or polydimethylsiloxane (PDMS) have been widely used in studying the responses of cells to electrical stimulation. However, unlike the numerous steps required to fabricate a PDMS device, the simple and rapid construction of the acrylic micro&#64258;uidic chip makes it suitable for both device prototyping and production. Yet none of the reported devices facilitate the efficient study of the simultaneous chemical and dcEF effects on cells. In this report, we describe our design and fabrication of an acrylic-based multichannel dual-electric-field (MDF) chip to investigate the concurrent effect of chemical and electrical stimulation on lung cancer cells. The MDF chip provides eight combinations of electrical/chemical stimulations in a single test. The chip not only greatly shortens the required experimental time but also increases accuracy in electrotaxis studies.

Many microfluidic devices have been developed for use in the study of electrotaxis. Yet, none of these chips allows the efficient study of the simultaneous chemical and electric-field (EF) effects on cells. We developed a polymethylmethacrylate-based device that offers better-controlled coexisting EF and chemical stimulation for use in electrotaxis research.

The behavior of directional cell migration under a direct current electric-field (dcEF) is referred to as electrotaxis. The significant role of ...

A Novel Bioreactor for High Density Cultivation of Diverse Microbial Communities

A novel reactor design, coined a high density bioreactor (HDBR), is presented for the cultivation and study of high density microbial communities. Past studies have evaluated the performance of the reactor for the removal of COD1 and nitrogen species2-4 by heterotrophic and chemoautotrophic bacteria, respectively. The HDBR design eliminates the requirement for external flocculation/sedimentation processes while still yielding effluent containing low suspended solids. In this study, the HDBR is applied as a photobioreactor (PBR) in order to characterize the nitrogen removal characteristics of an algae-based photosynthetic microbial community. As previously reported for this HDBR design, a stable biomass zone was established with a clear delineation between the biologically active portion of the reactor and the recycling reactor fluid, which resulted in a low suspended solid effluent. The algal community in the HDBR was observed to remove 18.4% of total nitrogen species in the influent. Varying NH4+ and NO3- concentrations in the feed did not have an effect on NH4+ removal (n=44, p=0.993 and n=44, p=0.610 respectively) while NH4+ feed concentration was found to be negatively related with NO3- removal (n=44, p=0.000) and NO3- feed concentration was found to be positively correlated with NO3- removal (n=44, p=0.000). Consistent removal of NH4+, combined with the accumulation of oxidized nitrogen species at high NH4+ fluxes indicates the presence of ammonia- and nitrite-oxidizing bacteria within the microbial community.

A novel reactor design, coined a high density bioreactor (HDBR), is presented for the cultivation and study of high density microbial communities. Here, the HDBR is successfully applied in a photobioreactor (PBR) configuration for the study of nitrogen metabolism by a mixed high density algal community.

A novel reactor design, coined a high density bioreactor (HDBR), is presented for the cultivation and study of high density microbial communities. Past ...

Design and Implementation of an Automated Illuminating, Culturing, and Sampling System for Microbial Optogenetic Applications

Optogenetic systems utilize genetically-encoded proteins that change conformation in response to specific wavelengths of light to alter cellular processes. There is a need for culturing and measuring systems that incorporate programmed illumination and stimulation of optogenetic systems. We present a protocol for building and using a continuous culturing apparatus to illuminate microbial cells with programmed doses of light, and automatically acquire and analyze images of cells in the effluent. The operation of this apparatus as a chemostat allows the growth rate and the cellular environment to be tightly controlled. The effluent of the continuous cell culture is regularly sampled and the cells are imaged by multi-channel microscopy. The culturing, sampling, imaging, and image analysis are fully automated so that dynamic responses in the fluorescence intensity and cellular morphology of cells sampled from the culture effluent are measured over multiple days without user input. We demonstrate the utility of this culturing apparatus by dynamically inducing protein production in a strain of Saccharomyces cerevisiae engineered with an optogenetic system that activates transcription.

We designed a continuous culturing apparatus for use with optogenetic systems to illuminate cultures of microbes and regularly image cells in the effluent with an inverted microscope. The culturing, sampling, imaging, and image analysis are fully automated so that dynamic responses to illumination can be measured over several days.

Optogenetic systems utilize genetically-encoded proteins that change conformation in response to specific wavelengths of light to alter cellular ...

Assembly and Tracking of Microbial Community Development within a Microwell Array Platform

The development of microbial communities depends on a combination of complex deterministic and stochastic factors that can dramatically alter the spatial distribution and activities of community members. We have developed a microwell array platform that can be used to rapidly assemble and track thousands of bacterial communities in parallel. This protocol highlights the utility of the platform and describes its use for optically monitoring the development of simple, two-member communities within an ensemble of arrays within the platform. This demonstration uses two mutants of Pseudomonas aeruginosa, part of a series of mutants developed to study Type VI secretion pathogenicity. Chromosomal inserts of either mCherry or GFP genes facilitate the constitutive expression of fluorescent proteins with distinct emission wavelengths that can be used to monitor community member abundance and location within each microwell. This protocol describes a detailed method for assembling mixtures of bacteria into the wells of the array and using time-lapse fluorescence imaging and quantitative image analysis to measure the relative growth of each member population over time. The seeding and assembly of the microwell platform, the imaging procedures necessary for the quantitative analysis of microbial communities within the array, and the methods that can be used to reveal interactions between microbial species area all discussed.

The development of microbial communities depends on a combination of factors, including environmental architecture, member abundance, traits, and interactions. This protocol describes a synthetic, microfabricated environment for the simultaneous tracking of thousands of communities contained in femtoliter wells, where key factors such as niche size and confinement can be approximated.

The development of microbial communities depends on a combination of complex deterministic and stochastic factors that can dramatically alter the spatial ...

Prospecting Microbial Strains for Bioremediation and Probiotics Development for Metaorganism Research and Preservation

Pollution affects all biomes. Marine environments have been particularly impacted, especially coral reefs, one of the most sensitive ecosystems on Earth. Globally, 4.5 billion people are economically dependent on the sea, where most of their livelihood is provided by coral reefs. Corals are of great importance and therefore their extinction leads to catastrophic consequences. There are several possible solutions to remediate marine pollutants and local contamination, including bioremediation. Bioremediation is the capacity of organisms to degrade contaminants. The approach presents several advantages, such as sustainability, relatively low cost, and the fact that it can be applied in different ecosystems, causing minimal impacts to the environment. As an extra advantage, the manipulation of endogenous microbiomes, including putative beneficial microorganisms for corals (pBMCs), may have probiotic effects for marine animals. In this context, the use of the two approaches, bioremediation and pBMC inoculation combined, could be promising. This strategy would promote the degradation of specific pollutants that can be harmful to corals and other metaorganisms while also increasing host resistance and resilience to deal with pollution and other threats. This method focuses on the selection of pBMCs to degrade two contaminants: the synthetic estrogen 17a-ethinylestradiol (EE2) and crude oil. Both have been reported to negatively impact marine animals, including corals, and humans. The protocol describes how to isolate and test bacteria capable of degrading the specific contaminants, followed by a description of how to detect some putative beneficial characteristics of these associated microbes to their coral host. The methodologies described here are relatively cheap, easy to perform, and highly adaptable. Almost any kind of soluble target compound can be used instead of EE2 and oil.

Pollution affects all biomes. Marine environments have been particularly impacted, especially coral reefs, one of the most sensitive ecosystems on Earth. Bioremediation is the capacity of organisms to degrade contaminants. Here, we describe methodologies to isolate and test microbes presenting bioremediation ability and potential probiotic characteristics for corals.

Pollution affects all biomes. Marine environments have been particularly impacted, especially coral reefs, one of the most sensitive ecosystems on Earth. ...

Process Optimization using High Throughput Automated Micro-Bioreactors in Chinese Hamster Ovary Cell Cultivation

Optimization of bioprocesses to increase the yield of desired products is of importance in the biopharmaceutical industry. This can be achieved by strain selection and by developing bioprocess parameters. Shake flasks have been used for this purpose. They, however, lack the capability to control the process parameters such as pH and dissolved oxygen (DO). This limitation can be overcome with the help of an automated micro-bioreactor. These bioreactors mimic cultivation at a larger scale. One of the major advantages of this system is the integration of the Design of Experiment (DOE) in the software. This integration enables establishing a design where multiple process parameters can be varied simultaneously. The critical process parameters and optimum bioprocess conditions can be analyzed within the software. The focus of the work presented here is to introduce the user to the steps involved in process design in the software and incorporation of the DOE within the cultivation run.

Here, we present a detailed procedure to run a Design of Experiment in an automated micro-bioreactor followed by cell harvest and protein quantification using a Protein A column.

Optimization of bioprocesses to increase the yield of desired products is of importance in the biopharmaceutical industry. This can be achieved by strain ...

Generating Controlled, Dynamic Chemical Landscapes to Study Microbial Behavior

We demonstrate a method for the generation of controlled, dynamic chemical pulses&#8213;where localized chemoattractant becomes suddenly available at the microscale&#8213;to create micro-environments for microbial chemotaxis experiments. To create chemical pulses, we developed a system to introduce amino acid sources near-instantaneously by photolysis of caged amino acids within a polydimethylsiloxane (PDMS) microfluidic chamber containing a bacterial suspension. We applied this method to the chemotactic bacterium, Vibrio ordalii, which can actively climb these dynamic chemical gradients while being tracked by video microscopy. Amino acids, rendered biologically inert (&#39;caged&#39;) by chemical modification with a photoremovable protecting group, are uniformly present in the suspension but not available for consumption until their sudden release, which occurs at user-defined points in time and space by means of a near-UV-A focused LED beam. The number of molecules released in the pulse can be determined by a calibration relationship between exposure time and uncaging fraction, where the absorption spectrum after photolysis is characterized by using UV-Vis spectroscopy. A nanoporous polycarbonate (PCTE) membrane can be integrated into the microfluidic device to allow the continuous removal by flow of the uncaged compounds and the spent media. A strong, irreversible bond between the PCTE membrane and the PDMS microfluidic structure is achieved by coating the membrane with a solution of 3-aminopropyltriethoxysilane (APTES) followed by plasma activation of the surfaces to be bonded. A computer-controlled system can generate user-defined sequences of pulses at different locations and with different intensities, so as to create resource landscapes with prescribed spatial and temporal variability. In each chemical landscape, the dynamics of bacterial movement at the individual scale and their accumulation at the population level can be obtained, thereby allowing the quantification of chemotactic performance and its effects on bacterial aggregations in ecologically relevant environments.

A protocol for the generation of dynamic chemical landscapes by photolysis within microfluidic and millifluidic setups is presented. This methodology is suitable to study diverse biological processes, including the motile behavior, nutrient uptake, or adaptation to chemicals of microorganisms, both at the single cell and population level.

We demonstrate a method for the generation of controlled, dynamic chemical pulses&#8213;where localized chemoattractant becomes suddenly available at the ...