We would like to thank the Canadian Foundation for Innovation, the British Columbia Knowledge Development Fund and the National Sciences and Engineering Research Council (NSERC) of Canada for supporting ongoing studies on low oxygen regions of coastal and open ocean waters. In addition, D.A.W. was supported by fellowships from NSERC, Killam and the TULA foundation funded Centre for Microbial Diversity and Evolution.

Part 1: Water Collection
<ol>
<li>Depths are assigned to each cast.</li>
<li>Depths to be sampled and the total volume to be collected for the current cast are determined.</li>
<li>It is ensured that the Go-Flo and Niskin bottles are open, and that their valves and spigots are closed.</li>
<li>The CTD is loaded onto bottom of the line and lower into water.</li>
<li>A bottle for the deepest depth sampled in cast first is loaded onto the line after the CTD; it is ensured that the line is properly fitted into bracket and the screws are tightened.</li>
<li>A messenger is attached to each bottle (except the deepest one) before lowering.</li>
<li>The line is lowered the distance between the first depth and the next; another bottle is then loaded. It should be noted that for depths where 20L are collected for filtration, a total of 2 12L bottles are loaded consecutively about .75m apart.</li>
<li>Once all the bottles are on the line, the line is lowered to the desired depth and 2 minutes are allowed to pass.</li>
<li>A messenger is sent down and a few minutes are allowed to pass to ensure that all bottles close.</li>
<li>The line is reeled in and the bottles are unloaded as they come up onto the racks.</li>
<li>For depths that require 20L samples for DNA and RNA, two Niskin bottles are collected. One bottle is used to sample the chemical parameters (see below), while the other is drained into the carboy. RNA is collected immediately from the second Niskin. The remainder of the first is also drained into the carboy to give ~20L final volume. For low-resolution samples only 1L of water is set aside for filtration in sterile Nalgene bottles.</li>
</ol>
Part 2: Gas sample collection
<ol>
<li>If oxygen samples are needed, they are collected first.</li>
<li>A piece of thin tubing is attached to the Niskin/Go-Flo spigot and the other end of the tubing is placed place into the glass serum bottles.</li>
<li>The serum bottle is rinsed 3 times with sample water, and filled to overflowing such that no air bubbles are present.</li>
<li>50&mu;l mercury chloride (HgCl2) are added to the serum bottle in a way that doesn't introduce air bubbles into the sample.</li>
<li>The bottle is sealed with a rubber stopper and crimped with an aluminum cap, and is then stored on ice in a cooler.</li>
</ol>
Part 3: Nutrient sample collection
<ol>
<li>A 60 cc syringe is rinsed with sample water, an (0.2 &mu;m) is attached in-line and some water is pushed through the acrodisc.</li>
<li>A polyethylene bottle is rinsed with ~10 ml filtered water 3 times (shake bottle when rinsing).</li>
<li>Filtered sample water is added to the bottles, about &frac34; full.</li>
<li>The sample is stored on ice in the cooler.</li>
</ol>
Part 4: Ammonia sample collection
<ol>
<li>Sample tubes are rinsed with sample water.</li>
<li>Sample tubes are filled completely with sample water.</li>
<li>5ml of sample water are taken out using a 10ml pipet; the rest of the water in the tube is discarded and the 5ml in the pipet tip are replaced into the sample tube.</li>
<li>7.5ml of ammonium working reagent is added to each tube once samples from all depths have been collected.</li>
</ol>
Part 5: Sample collection for cell enumeration
<ol><li>A pre-labelled 50 ml Falcon tube containing 5.4 ml 37%formaldehyde is filled to the top for a final concentration of 4%. Care is taken not to spill.</li></ol>
Part 6: Sample collection for hydrogen sulphide measurements
<ol>
<li>A pre-labelled 50 ml Falcon tube containing 20% zinc acetate (Zn(O2CCH3)2) is filled to the top. Care is taken not to spill.</li>
</ol>
Part 7: Small volume collection for biomass concentration
<ol>
<li>1-litre bottles are filled to the top.</li>
</ol>
Part 8: Large volume collection for biomass concentration
<ol>
<li>20-litre carboys are filled.</li>
</ol>
Part 9: Representative Results
The final outcome of seawater sampling results in approximately 12 dissolved oxygen samples, 32-48 gas samples, 16 nutrient samples, 32 ammonium samples, 16 hydrogen sulfide samples, 16 samples for cell counts, 6 20-litre carboys, 16 1-litre bottles and 4 Sterivex 0.22&mu;m filters containing microbial biomass preserved with RNA later.

<ol>
	<li>Cline, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spectrophotometric+determination+of+hydrogen+sulfide+in+natural+waters.">Spectrophotometric determination of hydrogen sulfide in natural waters.</a> Limnology &#38; Oceanography. 14, 454-458 (1969).</li><li>Holmes, R. M., Aminot, A., Kerouel, R., Hooker, B. A., Peterson, B. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+and+precise+method+for+measuring+ammonium+in+marine+and+freshwater+ecosystems.">A simple and precise method for measuring ammonium in marine and freshwater ecosystems.</a> Canadian Journal of fisheries and Aquatic Science. 56, 1801-1808 (1999).</li></ol>

The authors have nothing to disclose.

Overall, there is a great deal of preparation and planning required for this type of sampling, so budget 2 days before the trip to get things in order and one day afterwards for cleaning everything up. In general, do not let salt water come into contact with the peristaltic pump or into the aluminum Zarges box used to transport the field equipment. Treat the equipment with respect and it will perform well for a long time to come.

<table border="1">
		<thead>
		<tr>
		<th>Material Name</th>
		<th>Type</th>
		<th>Company</th>
		<th>Catalogue Number</th>
		<th>Comment</th>
		</tr>
		</thead>
		<tbody>
		
<tr>
<td>20L Carboys</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>02-960-15</td>
<td>&nbsp;</td>
<tr>
<td>3/8" Tygon</td>
<td>&nbsp;</td>
<td>Cole Parmer</td>
<td>06429-36</td>
<td>&nbsp;</td>
<tr>
<td>Sterivex filters</td>
<td>&nbsp;</td>
<td>Fisher</td>
<td>SVG010RS</td>
<td>&nbsp;</td>
<tr>
<td>Prefilter Housing Unit</td>
<td>&nbsp;</td>
<td>AMD</td>
<td>501200</td>
<td>&nbsp;</td>
<tr>
<td>Luer Fitting</td>
<td>&nbsp;</td>
<td>Cole Parmer</td>
<td>31507-27</td>
<td>&nbsp;</td>
<tr>
<td>1/4" Tygon tubing</td>
<td>&nbsp;</td>
<td>Cole Parmer</td>
<td>06429-24</td>
<td>&nbsp;</td>
<tr>
<td>1/4" Tygon tubing</td>
<td>&nbsp;</td>
<td>Cole Parmer</td>
<td>06429-24</td>
<td>&nbsp;</td>
<tr>
<td>1/4" Tygon tubing</td>
<td>&nbsp;</td>
<td>Cole Parmer</td>
<td>06429-24</td>
<td>&nbsp;</td>
<tr>
<td>50ml Plastic tubes</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Glass Serum Bottles</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>Glass Sample Collection</td>
</tr>
<tr>
<td>Septa and aluminum caps for glass serum bottles</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Hand Crimper</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>20-200ul Pipette and Tips</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Glass Tubes</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>Ammonium Sample Collection</td>
</tr>
<tr>
<td>30ml Plastic Bottles</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>Nutrient Collection</td>
</tr>
<tr>
<td>Acrodisc Filters</td>
<td>&nbsp;</td>
<td>Millipore</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>5 ml Tubes</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>Nitrite Sample Collection</td>
</tr>
<tr>
<td>37% Formaldehyde</td>
<td>Reagent</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>For cell count samples</td>
</tr>
<tr>
<td>20% Zinc Acetate</td>
<td>Reagent</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>For sulfide samples</td>
</tr>
<tr>
<td>Mercuric Chloride</td>
<td>Reagent</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>For gas samples</td>
</tr>
<tr>
<td>milliQ water</td>
<td>Reagent</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<tr>
<td>Ammonium Working Reagent</td>
<td>Reagent</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>Borate buffer, sodium sulfite, orthophaladialdehyde</td>
</tr>
<tr>
<td>Sulfanilamide</td>
<td>Reagent</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>5g into 450ml water and 50ml HCl</td>
</tr>
<tr>
<td>N-(1-naphthy)-ethylenediamine dihydrochloride solution</td>
<td>Reagent</td>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td>0.5g into 500ml water</td>
</tr>
</tbody>
</table>

seawater sampling and collection

This video documents methods for collecting coastal marine water samples and processing them for various downstream applications including biomass concentration, nucleic acid purification, cell abundance, nutrient and trace gas analyses. For today's demonstration samples were collected from the deck of the HMS John Strickland operating in Saanich Inlet. An A-frame derrick, with a multi-purpose winch and cable system, is used in combination with Niskin or Go-Flo water sampling bottles. Conductivity, Temperature, and Depth (CTD) sensors are also used to sample the underlying water mass. To minimize outgassing, trace gas samples are collected first.  Then, nutrients, water chemistry, and cell counts are determined. Finally, waters are collected for biomass filtration. The set-up and collection time for a single cast is ~1.5 hours at a maximum depth of 215 meters. Therefore, a total of 6 hours is generally needed to complete the collection series described here.

Watch this Scientific Journal Video about Seawater Sampling and Collection at JoVE.com

Seawater Sampling and Collection

This video documents methods for collecting coastal marine water samples and processing them for various downstream applications including biomass concentration, nucleic acid purification, cell abundance, nutrient and trace gas analyses.

This video documents methods for collecting coastal marine water samples and processing them for various downstream applications including biomass ...

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19.8K Views.  University of British Columbia - UBC. This video documents methods for collecting coastal marine water samples and processing them for various downstream applications including biomass concentration, nucleic acid purification, cell abundance, nutrient and trace gas analyses.

Video: Seawater Sampling and Collection

Collection and Cryopreservation of Hamster Oocytes and Mouse Embryos

Embryos and oocytes were first successfully cryopreserved more than 30 years ago, when Whittingham et al. 1 and Wilmut 2 separately described that mouse embryos could be frozen and stored at -196 &deg;C and, a few years later, Parkening et al. 3 reported the birth of live offspring resulting from in vitro fertilization (IVF) of cryopreserved oocytes. Since then, the use of cryopreservation techniques has rapidly spread to become an essential component in the practice of human and animal assisted reproduction and in the conservation of animal genetic resources. Currently, there are two main methods used to cryopreserve oocytes and embryos: slow freezing and vitrification. A wide variety of approaches have been used to try to improve both techniques and millions of animals and thousands of children have been born from cryopreserved embryos. However, important shortcomings associated to cryopreservation still have to be overcome, since ice-crystal formation, solution effects and osmotic shock seem to cause several cryoinjuries in post-thawed oocytes and embryos. Slow freezing with programmable freezers has the advantage of using low concentrations of cryoprotectants, which are usually associated with chemical toxicity and osmotic shock, but their ability to avoid ice-crystal formation at low concentrations is limited. Slow freezing also induces supercooling effects that must be avoided using manual or automatic seeding 4. In the vitrification process, high concentrations of cryoprotectants inhibit the formation of ice-crystals and lead to the formation of a glasslike vitrified state in which water is solidified, but not expanded. However, due to the toxicity of cyroprotectants at the concentrations used, oocytes/embryos can only be exposed to the cryoprotectant solution for a very short period of time and in a minimum volume solution, before submerging the samples directly in liquid nitrogen 5. In the last decade, vitrification has become more popular because it is a very quick method in which no expensive equipment (programmable freezer) is required. However, slow freezing continues to be the most widely used method for oocyte/embryo cryopreservation. In this video-article we show, step-by-step, how to collect and slowly freeze hamster oocytes with high post-thaw survival rates. The same procedure can also be applied to successfully freeze and thaw mouse embryos at different stages of preimplantation development.

In this video-article we present a step-by-step demonstration on how to collect and cryopreserve hamster oocytes with high post-thaw survival rates. The same procedure can also be applied to successfully freeze and thaw mouse embryos at different stages of preimplantation development.

Embryos and oocytes were first successfully cryopreserved more than 30 years ago, when Whittingham et al. 1 and Wilmut 2 separately described that mouse ...

Large Volume (20L+) Filtration of Coastal Seawater Samples

The workflow begins with the collection of coastal marine waters for downstream microbial community, nutrient and trace gas analyses. For this method, samples were collected from the deck of the HMS John Strickland operating in Saanich Inlet. This video documents large volume (&ge;20 L) filtration of microbial biomass, ranging between 0.22&mu;m and 2.7&mu;m in diameter, from the water column. Two 20L samples can be filtered simultaneously using a single pump unit equipped with four rotating heads. Filtration is done in the field on extended trips, or immediately upon return for day trips. It is important to record the amount of water passing through each sterivex filter unit. To prevent biofilm formation between sampling trips, all filtration equipment must be rinsed with dilute HCl and deionized water and autoclaved immediately after use. This procedure will take approximately 5 hours plus an additional hour for clean up.

Large Volume 20L+ Filtration of Coastal Seawater Samples

This video documents large volume (&ge;20 L) filtration of microbial biomass, ranging between 0.22&mu;m and 2.7&mu;m in diameter, from the water column.

The workflow begins with the collection of coastal marine waters for downstream microbial community, nutrient and trace gas analyses. For this method, ...

Small Volume (1-3L) Filtration of Coastal Seawater Samples

The workflow begins with the collection of coastal marine waters for downstream microbial community, nutrient and trace gas analyses. For today s demonstration samples were collected from the deck of the HMS John Strickland operating in Saanich Inlet. This video documents small volume (~1 L) filtration of microbial biomass from the water column. The protocol is an extension of the large volume sampling protocol described earlier, with one major difference: here, there is no pre-filtration step, so all size classes of biomass are collected down to the 0.22 &mu;m filter cut-off. Samples collected this way are ideal for nucleic acid analysis. The set-up, filtration, and clean-up steps each take about 20-30 minutes. If using two peristaltic pumps simultaneously, up to 8 samples may be filtered at the same time. To prevent biofilm formation between sampling trips, all filtration equipment must be rinsed with dilute HCl and deionized water and autoclaved immediately after use.

Small Volume 1-3L Filtration of Coastal Seawater Samples

This video documents small volume (~1 L) filtration of microbial biomass from the water column.

The workflow begins with the collection of coastal marine waters for downstream microbial community, nutrient and trace gas analyses. For today s ...

Diagnostic Necropsy and Selected Tissue and Sample Collection in Rats and Mice

There are multiple sample types that may be collected from a euthanized animal in order to help diagnose or discover infectious agents in an animal colony. Proper collection of tissues for further histological processing can impact the quality of testing results. This article describes the conduct of a basic gross examination including identification of heart, liver, lungs, kidneys, and spleen, as well as how to collect those organs. Additionally four of the more difficult tissue/sample collection techniques are demonstrated. Lung collection and perfusion can be particularly challenging as the tissue needs to be properly inflated with a fixative in order for inside of the tissue to fix properly and to enable thorough histologic evaluation. This article demonstrates the step by step technique to remove the lung and inflate it with fixative in order to achieve optimal fixation of the tissue within 24 hours. Brain collection can be similarly challenging as the tissue is soft and easily damaged. This article demonstrates the step by step technique to expose and remove the brain from the skull with minimal damage to the tissue. The mesenteric lymph node is a good sample type in which to detect many common infectious agents as enteric viruses persist longer in the lymph node than they are shed in feces. This article demonstrates the step by step procedure for locating and aseptically removing the mesenteric lymph node. Finally, identification of infectious agents of the respiratory tract may be performed by bacterial culture or PCR testing of nasal and/or bronchial fluid aspirates taken at necropsy. This procedure describes obtaining and preparing the respiratory aspirate sample for bacterial culture and PCR testing.

This article describes the procedures for conducting a basic postmortem examination of a mouse or rat, and the collection of basic organs, as well as more challenging sample types from for histological, microbiological, and PCR evaluation.

There are multiple sample types that may be collected from a euthanized animal in order to help diagnose or discover infectious agents in an animal ...

Milk Collection Methods for Mice and Reeves' Muntjac Deer

Animal models are commonly used throughout research laboratories to accomplish what would normally be considered impractical in a pathogen&#8217;s native host. Milk collection from animals allows scientists the opportunity to study many aspects of reproduction including vertical transmission, passive immunity, mammary gland biology, and lactation. Obtaining adequate volumes of milk for these studies is a challenging task, especially from small animal models. Here we illustrate an inexpensive and facile method for milk collection in mice and Reeves&#8217; muntjac deer that does not require specialized equipment or extensive training. This particular method requires two researchers: one to express the milk and to stabilize the animal, and one to collect the milk in an appropriate container from either a Muntjac or mouse model. The mouse model also requires the use of a P-200 pipetman and corresponding pipette tips. While this method is low cost and relatively easy to perform, researchers should be advised that anesthetizing the animal is required for optimal milk collection.

Milk Collection Methods for Mice and Reeves&#039; Muntjac Deer

Milk collection from animal models facilitates various research avenues: understanding passive immunity, identifying pathogens responsible for vertical transmission and, through the use of transgenic mice, even commercial production of proteins found in human breast milk. Here we illustrate a simple method for milk collection in mice and Reeves&#8217; muntjac deer.

Animal models are commonly used throughout research laboratories to accomplish what would normally be considered impractical in a pathogen&#8217;s native ...

Non-Terminal Blood Sampling Techniques in Guinea Pigs

Guinea pigs possess several biological similarities to humans and are validated experimental animal models1-3. However, the use of guinea pigs currently represents a relatively narrow area of research and descriptive data on specific methodology is correspondingly scarce. The anatomical features of guinea pigs are slightly different from other rodent models, hence modulation of sampling techniques to accommodate for species-specific differences, e.g., compared to mice and rats, are necessary to obtain sufficient and high quality samples. As both long and short term in vivo studies often require repeated blood sampling the choice of technique should be well considered in order to reduce stress and discomfort in the animals but also to ensure survival as well as compliance with requirements of sample size and accessibility. Venous blood samples can be obtained at a number of sites in guinea pigs e.g., the saphenous and jugular veins, each technique containing both advantages and disadvantages4,5. Here, we present four different blood sampling techniques for either conscious or anaesthetized guinea pigs. The procedures are all non-terminal procedures provided that sample volumes and number of samples do not exceed guidelines for blood collection in laboratory animals6. All the described methods have been thoroughly tested and applied for repeated in vivo blood sampling in studies within our research facility.

Though a known model, the guinea pig currently represents a niche in experimental animal sciences and limited data is available on the execution of most procedures. Here we present four different approaches to non-terminal in vivo blood sampling techniques in either conscious or anaesthetized guinea pigs.

Guinea pigs possess several biological similarities to humans and are validated experimental animal models1-3. However, the use of guinea pigs currently ...

Sampling Blood from the Lateral Tail Vein of the Rat

Blood samples are commonly obtained in many experimental contexts to measure targets of interest, including hormones, immune factors, growth factors, proteins, and glucose, yet the composition of the blood is dynamically regulated and easily perturbed. One factor that can change the blood composition is the stress response triggered by the sampling procedure, which can contribute to variability in the measures of interest. Here we describe a procedure for blood sampling from the lateral tail vein in the rat. This procedure offers significant advantages over other more commonly used techniques. It permits rapid sampling with minimal pain or invasiveness, without anesthesia or analgesia. Additionally, it can be used to obtain large volume samples (upwards of 1 ml in some rats), and it may be used repeatedly across experimental days. By minimizing the stress response and pain resulting from blood sampling, measures can more accurately reflect the true basal state of the animal, with minimal influence from the sampling procedure itself.

Blood samples are useful for assessing biomarkers of physiological states or disease in vivo. Here we describe the methodology to sample blood from the lateral tail vein in the rat. This method provides rapid samples with minimal pain and invasiveness.

Blood samples are commonly obtained in many experimental contexts to measure targets of interest, including hormones, immune factors, growth factors, ...

Collection and Identification of Pollen from Honey Bee Colonies

Researchers often collect and analyze corbicular pollen from honey bees to identify the plant sources on which they forage for pollen or to estimate pesticide exposure of bees via pollen. Described herein is an effective pollen-trapping method for collecting corbicular pollen from honey bees returning to their hives. This collection method results in large quantities of corbicular pollen that can be used for research purposes. Honey bees collect pollen from many plant species, but typically visit one species during each collection trip. Therefore, each corbicular pollen pellet predominantly represents one plant species, and each pollen pellet can be described by color. This allows the sorting of samples of corbicular pollen by color to segregate plant sources. Researchers can further classify corbicular pollen by analyzing the morphology of acetolyzed pollen grains for taxonomic identification. These methods are commonly used in studies related to pollinators such as pollination efficiency, pollinator foraging dynamics, diet quality, and diversity. Detailed methodologies are presented for collecting corbicular pollen using pollen traps, sorting pollen by color, and acetolyzing pollen grains. Also presented are results pertaining to the frequency of pellet colors and taxa of corbicular pollen collected from honey bees in five different cropping systems.

We describe methods for collecting corbicular pollen from honey bees as well as protocols for color sorting, acetolysis, and microscope slide preparation of pollen for taxonomic identification. In addition, we present pellet color and taxonomic diversity of corbicular pollen collected from five cropping systems using pollen traps.

Researchers often collect and analyze corbicular pollen from honey bees to identify the plant sources on which they forage for pollen or to estimate ...

Cryo-Electron Tomography Remote Data Collection and Subtomogram Averaging

Cryo-electron tomography (cryo-ET) has been gaining momentum in recent years, especially since the introduction of direct electron detectors, improved automated acquisition strategies, preparative techniques that expand the possibilities of what the electron microscope can image at high-resolution using cryo-ET and new subtomogram averaging software. Additionally, data acquisition has become increasingly streamlined, making it more accessible to many users. The SARS-CoV-2 pandemic has further accelerated remote cryo-electron microscopy (cryo-EM) data collection, especially for single-particle cryo-EM, in many facilities globally, providing uninterrupted user access to state-of-the-art instruments during the pandemic. With the recent advances in Tomo5 (software for 3D electron tomography), remote cryo-ET data collection has become robust and easy to handle from anywhere in the world. This article aims to provide a detailed walk-through, starting from the data collection setup in the tomography software for the process of a (remote) cryo-ET data collection session with detailed troubleshooting. The (remote) data collection protocol is further complemented with the workflow for structure determination at near-atomic resolution by subtomogram averaging with emClarity, using apoferritin as an example.

The present protocol describes high-resolution cryo-electron tomography remote data acquisition using Tomo5 and subsequent data processing and subtomogram averaging using emClarity. Apoferritin is used as an example to illustrate detailed step-by-step processes to achieve a cryo-ET structure at 2.86 &#197; resolution.

Cryo-electron tomography (cryo-ET) has been gaining momentum in recent years, especially since the introduction of direct electron detectors, improved ...