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Method Article
This protocol details the assembly of mini-bioreactor arrays to be utilized for continuous flow culture of complex fecal communities under anaerobic conditions. We also discuss the methods for assembly, inoculation, and sampling of the reactors for further analysis.
The microbiota, especially bacteria, respond to various environmental exposures such as micro and macronutrients, pharmacological compounds, and inflammatory mediators, which dynamically alter community composition and microbial metabolic output. Understanding how physiological culture conditions affect microbial communities and diversity and their metabolic capacity will contribute important knowledge of their impact on health and diseases. Here, we present a protocol adapted from the template published by Auchtung et al. to create mini-bioreactor arrays that can cultivate complex fecal communities, define bacterial consortiums or single strains under precise conditions, including nutrient availability, temperature, flow rate, pH, and oxygen content. We describe the process for building the mini-bioreactor system, including adaptations to improve limitations in the published protocol. We also discuss the setup of the mini-bioreactor system under anaerobic conditions with the use of MEGA media (adapted from Han et al.), which is a rich media supporting the growth of diverse bacteria. We describe the inoculation of gut humanized mouse fecal samples into the mini-bioreactor system, followed by the establishment of complex community cultures within the mini-bioreactor system, which can be grown under continuous flow with aseptic sampling to monitor community composition. This system is adaptable to dietary changes and other cultural modifications. The techniques described here allow for the characterization of diverse, fastidious fecal communities under dynamic conditions or in response to perturbation in isolation from host-derived factors.
The gut microbiota is a vast network of microorganisms, including bacteria, fungi, archaea, and viruses, which contain a huge genetic and metabolic repertoire that greatly outnumbers that of a human host1. The microbiome's rich metabolic capacity includes metabolites produced from bacterial processing of dietary nutrients, host metabolites chemically modified by bacteria, and metabolites synthesized uniquely by the microbiota2. Microbiota is implicated in nearly all host bioprocesses but also in disease states like inflammatory bowel disease, cancer, metabolic disorders, and even neurological disorders2,3. Dissecting the contribution of the microbiota from that of the host is essential to understanding the role of specific microorganisms or complex communities in health and disease. One approach that enables this dissection is the use of microbial bioreactors, which cultivate diverse microbial communities under dynamic conditions. There are many commercially available bioreactors that allow for the growth of fecal bacterial communities for almost any purpose, including large-scale bioproduct cultivation or precise control of specific nutritive factors for the study of metabolic processes. However, these systems are enormously costly and require extensive preparation, and do not enable diverse experimental conditions to be examined in parallel. For a simplified approach that is less costly, more adaptable, and allows for many parallel conditions, we present here the protocol for the setup and use of a mini-bioreactor array under continuous flow adapted from Auchtung et al.4.
The complete setup of the mini-bioreactor system is demonstrated in Figure 1A. This mini-bioreactor system uses arrays of 6 reactor wells, which are completely independent of one another and are set up in an anaerobic chamber under peristaltic flow to enable continuous media delivery and removal (Figure 1A). Each reactor array sits on a 60-position magnetic stir plate, with two 48-cassette peristaltic pumps holding 2-stop tubing for the source media and waste flow (Figure 1A). The anaerobic chamber is equipped with a CAM-12 anaerobic monitor for oxygen content, a catalyst box to remove oxygen with heating capacity, and a hydrogen sulfide removal column to absorb excess gas from bacterial metabolism. Each reactor well is equipped with a source media inlet, waste outlet, and sample port, which allows for inoculation or sampling of each individual reactor well (Figure 1B).
As described, the bioreactor system enables dynamic control over temperature, media consumption, and nutrient availability to support the cultivation and maintenance of fecal communities. Temperature is modulated by a catalyst box with heating capacity, enabling changes in temperature throughout the entire anaerobic chamber to be implemented quickly. Media consumption is regulated by peristaltic pump flow rates, which can be modified to change media turnover in the reactors. Media turnover can be customized to the community types being cultivated in reactors, for example, being adapted for slow-growing or very quickly growing target strains. Lastly, nutrient availability can be dynamically modified by adding components through the individual sample ports for each reactor well. Static conditions that can be modified at the outset of an experiment, but which do not have dynamic control in the system are media type, oxygen content, and number of simultaneous reactors. Investigators can choose to implement any source media they wish, and while one media is described here, endless other source media types have been successfully implemented. One can operate the reactors under aerobic or microaerophilic conditions (depending on the availability of a microaerophilic chamber). Lastly, as many or as few reactors as needed can be set up depending on the experimental needs of the investigator. While reactors are in sets of six within an array, each reactor operates independently of the others, and each can be linked to a different source if desired.
This modular bioreactor system can be completely set up for around $25,000 (not including the anaerobic chamber or chamber-specific components), with the only non-reusable part being the tubing which can be replaced for less than $100 per run of the system. The system is mostly automated but does require daily checking for media levels as media source bottles will need to be changed over when empty. Additionally, any sampling must be completed manually, and any dynamic conditional changes to the system will need to be initiated manually (for example, changing the temperature). From the original system protocol published by Auchtung et al., a few modifications were implemented to improve overall performance and utility4. Firstly, the material for 3D printing of the bioreactor array is modified to be ABS-like Translucent Clear Plastic to improve the structural integrity of the system through repeated rounds of autoclaving. Additionally, in place of the 1/8 inch (3.2 mm) OD PTFE tubing, E-LFL, 2.06 mm ID, 100 ft tubing is instead used due to the sturdier material, which is more resistant to collapse, which would cause blockages in flow in the system. Lastly, an additional fitting using 1/4 -28 mm thread to barbed male adaptors is used to reduce changes in tube slippage from media source bottles. From Han et al., the adapted MEGA media recipe provides an undefined, complex, highly rich media that enables the cultivation of fastidious anaerobic microorganisms5. The media is modified to utilize alternative preparation of the histidine-hematin component, as the original is no longer commercially available. Sodium hydroxide is also used to pH the media to 7.0 or any desired pH. Overall, this system is budget and user-friendly, optimized, and an excellent entry point to continuous flow culture systems.
In this protocol, we describe in detail the setup of this mini-bioreactor array system, including materials, sterilization of the system, and subsequent usage for cultivation of gut humanized murine fecal samples. The overall goal of this method is to build an adaptable and cost-effective bioreactor system that can be utilized for cultivating microbial communities under controlled conditions. A detailed schematic of the workflow for the assembly of the mini-bioreactor system is provided in Figure 2 and referenced at appropriate steps within the protocol. In our example, we inoculate two reactors with the same fecal sample from humanized gut mice and describe microbial community structure under a continuous flow of MEGA media.
Figure 1: Schematic diagram of mini-bioreactor array setup in the anaerobic chamber. (A) Full view of the completed mini-bioreactor array setup in the anaerobic chamber. The 6-well bioreactor array is situated on the 60-position magnetic stir plate. The source luer tee network is attached to the source media on the left-hand side through the two-hole bottle cap. Two peristaltic pumps hold the 2-stop tubing from the source and waste networks on the left and right, respectively. The waste luer tee network empties into the waste bottle on the right-hand side. Essential equipment for the operation of the anaerobic chamber, including the CAM-12 monitor, catalyst box with heating capacity, and hydrogen sulfide removal column, are arranged within the chamber around the array system. (B) Top view of the source, sample, and waste ports attached to one reactor well with media at the appropriate height in the reactor. Please click here to view a larger version of this figure.
Figure 2: Schematic diagram of mini-bioreactor array assembly workflow. (A) Top-down view of the mini-bioreactor array, showing the orientation of the source, waste, and sample ports. (B) Side view of the mini-bioreactor array with view illustrating steps 2.3-2.4 of the protocol. The 1/8 inch PTFE tubing and fitting (1) are attached and inserted into the waste and sample ports. Fitting (1) without PTFE is inserted into the source port. (C) Side view of mini-bioreactor array illustrating steps 2.5-2.6 of the protocol. Fitting (2) is attached to the source and waste ports. Fitting (3) is attached to the sample port, and to that, fitting (4) is inserted on top. (D) Side view of mini-bioreactor array illustrating steps 2.9-2.11. E-LFL 2.06 mm tubing is connected to the source and waste ports, and the other end is connected to fittings (5) and then (6). 2-stop tubing of the appropriate diameter is then connected to fitting (6). The reverse connection is then repeated at the end of the 2-stop tubing, with fitting (6) connecting to the 2-stop tubing and fitting (5) connecting to that. Lastly, E-LFL 2.06 mm tubing will be connected to fitting (5) for connection to the luer tee network. (E) Top-down view of mini-bioreactor array displaying the source and waste luer tee network setup described in steps 2.12-2.15. E-LFL 2.06 mm tubing ending in fitting (5) is used to connect each reactor to several fittings (7), the last opening of which is connected to the cap on the source or waste bottle. (F) Side view of two-hole bottle cap assembly described in steps 2.16-2.17. One opening in the cap is connected to PTFE tubing that is placed inside the bottle. To that opening is inserted fitting (1), followed by fitting (2), and E-LFL 2.06 mm tubing connected to fitting (5). This fitting is attached to the source or waste luer network. To the opening not connected to PTFE tubing, fitting (1) is inserted, followed by fitting (2), and E-LFL 2.06 mm tubing is connected to another fitting (5). This end is capped with foil during autoclave sterilization for future attachment to a sterile 0.22 µM syringe filter. Please click here to view a larger version of this figure.
Fecal samples used in this study were obtained from experiments approved by the Institutional Animal Care and Use Committee (IACUC) at the University of Florida (UF) and performed at UF Animal Care Facilities (IACUC Protocol #IACUC202300000005). Briefly, mixed gender germ-free wild-type (GF WT; C57BL/6) mice (bred and maintained in isolators by UF Animal Care Services Germ-free Division) were transferred from breeding isolators and placed into the ISOcage P Bioexclusion system to allow for microbial manipulation. Equal colony-forming units (CFU) from human donor feces were pooled for gavage into mice. Two weeks post-inoculation, fecal samples were collected from these mice aseptically for storage and subsequent use in this protocol.
NOTE: Fecal sample collection and preparation described here are only intended as an example of a proper procedure, as depending on the type of samples collected (human, mouse, other animal) and the storage of these samples, this procedure can vary widely. Individuals should refer to the appropriate literature to design a protocol for fecal sample collection and preservation based on the needs of the individual researcher.
1. Typical preparation of fecal samples for -80 °C storage
2. Building a 6-well reactor array
3. MEGA media preparation
4. Array setup in anaerobic chamber
NOTE: It is essential to clean the interior of the hood and the hood gloves with 3% hydrogen peroxide followed by triple deionized water rinse to ensure no surface contamination prior to assembly. If the connections are made quickly following the removal of the foil, and no direct contact is made with the interior of the fittings and the anaerobic chamber gloves, there is minimal chance of contamination
5. Fecal sample inoculation
6. Aseptic collection of samples from reactor wells
7. Deconstructing and cleaning the mini-bioreactor system
Fecal samples were collected from mice colonized with human fecal slurry 2 weeks post-inoculation and stored at -80 °C. The bioreactor system was set up with continuous MEGA media flow for two replicate reactor wells (Figure 3A). The fecal slurry was prepared from the mouse fecal pellets according to the protocol described in step 6, and both reactors were inoculated by sample port with the responder mouse fecal slurry. After overnight incubation of the ...
The mini-bioreactor system described in this protocol enables the cultivation of independent fecal communities for parallel experimentation. This ability to study microbial communities in isolation of host factors is an essential approach to understanding the intrinsic capacity of microorganisms to adapt to their environment. This protocol can be easily adapted for the cultivation of defined bacterial consortia or even single isolate cultures if desired. The MEGA media described here is a rich, anaerobic broth designed f...
The authors have no conflicts of interest.
The authors are grateful to Josee Gauthier for the assistance with 16S rRNA gene sequencing. This research was supported, in part, by the UF Health Cancer Center Funds (C.J.) and UF Department of Medicine Gatorade Fund (C.J.). R.Z.G. was supported by UF Health Cancer Center funds. R.C.N. was supported by the National Institutes of Health TL1 Training Grant at the University of Florida (TL1TR001428, UL1TR001427), the National Cancer Institute of the National Institutes of Health Team-Based Interdisciplinary Cancer Research Training Program award T32CA257923 and the UF Health Cancer Center. Research reported in this publication was supported by the UF Health Cancer Center, supported in part by state appropriations provided in Fla. Stat. § 381.915 and the National Cancer Institute of the National Institutes of Health under Award Number P30CA247796. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health or the State of Florida. The funders had no role in study design, data collection, and analysis; decision to publish; or preparation of the manuscript.
Name | Company | Catalog Number | Comments |
1 mL BD Slip Tip Syringe sterile, single use | Fisher Scientific | 309659 | |
1/4-28 mm thread to barbed male adaptor (3.2 mm), 5/pack | Cole-Parmer | 008NB32-KD5L | To build 1 6-well array, need 2 packs |
10M NaOH (Sodium Hydroxide) | Sigma | 72068-100ML | |
2.0ml Screw Cap Tube, NonKnurl, Skirted,Natural, E-Beam Sterile tube w/ attached cap | Fisher Scientific | 14-755-228 | |
2mag MIXdrive 60 Stirring Drive | 2mag | 40060 | 60-position magnetic stir plate (optional addition of heating capacity- cat# 40260) |
6-well reactor arrray, ABS-Like Translucent Clear plastic | Protolabs | Custom | See supplementary files for .stl file for 3D printing |
Absolute Ethanol (200 Proof) | Fisher Scientific | BP2818 | |
Acetic acid, glacial | Sigma | A6283 | |
Adapter, nylon, male luer to 1/4-28 thread, 25/pack | Cole-Parmer | EW-45505-82 | To build 1 6-well array, need 6 (1 pack) |
Aluminum foil | Fisher Scientific | 01-213-100 | |
Anaerobic chamber | Coy Lab Products | Type B | |
Bel-Art SP Scienceware Flea Micro Spinbar Magnetic Stirring Bars (1/pk) | Fisher Scientific | 22-261679 | To build 1 6-well array, need 6 |
Biosafety cabinet class 2 | Nuaire | ||
Butyric acid | Sigma | B103500 | |
CaCl2 · 2H2O (Calcium Chloride Dihydrate) | Sigma | C7902 | |
Clorox Healthcare Germicidal Wipes With Bleach, Unscented, 6" x 5", Pack Of 150 Wipes | Office Depot | 129202 | |
D-(-)-Fructose | Sigma | F0127-100G | |
D-(+)-Cellobiose | Sigma | C7252-100G | |
D-(+)-Glucose | Sigma | G8270-100G | |
D-(+)-Maltose monohydrate | Sigma | M5885-100G | |
Drill America Plug Hand Tap DWTP1/4-28 | Home Depot | 305699489 | |
Dulbecco's Phosphate Buffered Saline, 1X without Ca and Mg, Sterile | Genesee | 25-508 | |
Female luer × 1/16″ hose barb adapter, Nylon, 25/pack | Cole-Parmer | EW-45502-00 | To build 1 6-well array, need 24 (1 pack) |
Female luer × 1/8″ hose barb adapter, Nylon 25/pack | Cole-Parmer | EW-45502-04 | To build 1 6-well array, need 6 (1 pack) |
Female luer × 3/32″ hose barb adapter, Nylon, 25/ pack | Cole-Parmer | EW-45502-02 | To build 1 6-well array, need 6 (1 pack) |
Female luer tee, Nylon, 25/pack | Cole-Parmer | EW-45502-56 | To build 1 6-well array, need 10 (1 pack) |
FeSO4 · 7H2O (Iron [II] Sulfate Heptahydrate) | Sigma | F8633 | |
Hematin | Sigma | H3281 | |
Histidine | Sigma | H7750 | |
Isovaleric acid | Sigma | 129542 | |
K2HPO4 dibasic (dipotassium hydrogen phosphate) | Sigma | P2222-1KG | |
KH2PO4 monobasic (potassium dihydrogen phosphate) | Sigma | P0662-500G | |
Large Orifice Pipet Tips | Fisher Scientific | 02-707-134 | |
L-Cysteine hydrochloride | Sigma | C1276-10G | |
Male luer with lock ring × 1/8″ hose barb adapter, Nylon, 25/pack | Cole-Parmer | EW-45505-04 | To build 1 6-well array, need 42 (2 packs) |
Meat extract | Sigma | 70164-500G | |
Med Vet International Exel Needle, 20G X 1", Hypodermic, 100/Box, 26417 | Fisher Scientific | 50-209-2532 | |
Menadione (Vitamin K3) | Sigma | M5625 | |
MgSO4 · 7H2O (Magnesium Sulfate Heptahydrate) | Sigma | M1880-500G | |
Milli-Q water | |||
NaCl (Sodium Chloride) | Sigma | S9888-500G | |
NaHCO3 (Sodium Bicarbonate) | Sigma | S5761-500G | |
Omnifi t Q-series two hole bottle cap | Cole-Parmer | 00945Q-2 | To build 1 6-well array, need 1 |
PMP IPC-N L 24CHNL 8RLR 115V | MasterFlex | ISM939C-115V | 24-channel peristaltic pump, require 1 for source and 1 for waste |
Precision Seal® rubber septa,white, 7 mm O.D. glass tubing (100/pk) | Millipore Sigma | Z553905-100EA | To build 1 6-well array, need 6 septa |
Propionic acid | Sigma | P5561 | |
Pump Tubing, 2-Stop, Tygon S3 E-Lab, 1.02 mm ID; 12/PK | VWR | MFLX96460-28 | To build 1 6-well array, need 6 (1 pack) |
Pump Tubing, 2-Stop, Tygon S3 E-Lab, 1.14 mm ID; 12/PK | VWR | MFLX96460-30 | To build 1 6-well array, need 6 (1 pack) |
Puritan Cary-Blair Medium, 5 ml | Fisher Scientific | 22-029-646 | |
PYREX 2L Round Media Storage Bottles, with GL45 Screw Cap | Fisher Scientific | 06-414-1E | |
Razor Blades | Genesee | 12-640 | |
Resazurin, sodium salt | ACROS Organics from ThermoFisher | AC41890-0010 | |
Soluble starch | Sigma | S9765-100G | |
Stainless Steel Micro Spatulas, spoon like blade | Fisher Scientific | S50823 | |
TBNG TYGON ELFL 2.06MMID 100' | VWR | MFLX06449-42 | To build 1 6-well array, need 205.5 cm |
Trace Mineral Supplement | ATCC | MD-TMS | |
Trypticase Peptone (BBL) | Fisher Scientific | B11921 | |
Tubing, PTFE, 1/8″ (3.2 mm) OD × 1.5 mm ID, 10 M | Cole-Parmer | 008 T32-150-10 | To build 1 6-well array, need 300 mm |
Tween 80 | Sigma | P1754 | |
Vitamin Supplement | ATCC | MD-VS | |
Yeast Extract (Bacto) | Fisher Scientific | DF0127-17-9 |
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