Shewanella: Sneaky Sulfur Cyclers?

Katherine Mateos, Carleton College

Like Shewanella, I too thrive at cold temperatures!

Life can survive almost anywhere! From hot pools on volcanoes to beneath ice-cold glaciers, pretty much all of the inhabitants in these hostile environments are so small that you cannot see them with your bare eye. These extremophiles, as they are often called, include tiny single-celled microbes—bacteria and archaea. By studying tiny microbes we can answer big questions: How did life begin on Earth?  How can we find life on other planets? How will our planet respond to its changing climate?

Outflow of Blood Falls on the Taylor Glacier. Image credit: Dr. Jill Mikucki.

This summer, I am working with one of these extremophiles, a type of bacteria separated out from a sample from Blood Falls, Antarctica. This lake is a pool of brine (very salty water) covered by more than 150 feet of ice from the Taylor Glacier. Blood Falls gets its name from the bright red stain that the brine leaves on the Taylor glacier as it leaks out from beneath the glacier. As you would expect, this location is cold and dark, but the chemicals in the brine are what truly make this ecosystem extreme. For one, Blood Falls is super salty, over twice as salty as the ocean. Most water has oxygen trapped within it, but Blood Falls has very little. Two important chemicals are also found in unusually high quantities: iron and sulfur.

Electron Microscope image of Shewanella BF02. Image credit: Bruce Boles.

The bacteria that I am studying makes good use of the iron in this environment. Like a battery produces energy from a variety of chemical reactions, Shewanella (strain BF02) gets most of its energy by harnessing the energy that is released when one chemical form of iron changes to another. However, there might be another source of energy Shewanella can live off of—perhaps a chemical that contains sulfur. Sulfur is one of the most common elements on earth, found in pesticides, foods, and in humans. Sulfur can form compounds with other common elements including hydrogen, carbon, and oxygen. Some of these chemicals, known as volatile organic sulfur compounds (VOSCs), easily evaporate into our atmosphere and affect our environment. We want to know if the Shewanella are creating these VOSCs, and if they do, what chemicals the Shewanella turn into VOSCs.

The strain of Shewanella that I am studying is from an extreme ecosystem but similar Shewanella are found throughout many ocean ecosystems. We can treat Blood Falls as a model to learn about the way that our oceans will affect our environment.  Even though Shewanella are too small to see with your bare eyes, figuring out what compounds they break down can help us understand the future of the environment around the world.

Thank you to my mentor, Dr. Peter A. Lee, and our collaborators, Dr. Jill Mikucki and Abigail Jarratt, for their guidance in the research process. This project is supported by the Fort Johnson REU Program, NSF DBI-1757899.

References

Mikucki, J. A. et al. A contemporary microbially maintained subglacial ferrous ‘ocean’. Science 324, 397–400 (2009).

Sievert, S. M., Kiene, R. P. & Schulz-Vogt, H. N. The sulfur cycle. Oceanography 20, 117–123 (2007).

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Uncovering Seasonal Changes in the Algae Our Oceans Depend On

Emily Spiegel, Bryn Mawr College

As described in my previous posts, this study focused on a polar diatom, F. cylindrus.  Despite the harsh temperatures of its habitat, this diatom is awesomely productive. It can form blooms under sea ice so thick, it looks like grass! Marine organisms feed on these blooms, which contributes to productivity of the entire ecosystem.

Because the poles are situated at the ends of the Earth, they are subject to constant changes in light availability, from continuous light to continuous darkness. How are photosynthetic organisms like F. cylindrus able to adapt to this stressful change? Their ability to produce biomass is dependent on light levels: too much and these cells can be overwhelmed, too little and there may not be enough to balance against the costs of respiration.

I found that in the low light exposure of polar autumn (6h light: 18h darkness), F. cylindrus begins to reproduce sexually, instead of asexually. This was found through analysis of RNA expression, which is an indicator for how much a certain gene is being transcribed into proteins to do work within the cell. Sexual reproduction leaves behind a trace in the RNA, based on the particular genes involved. As opposed to the primary form of diatom reproduction (asexual), sexual reproduction conserves resources and produces fewer cells. So the population does not grow to the same extent as populations reproducing asexually, but it’s also able to survive in stressful and changing conditions better than asexual populations.

Interestingly, stress can also reduce the ability of F. cylindrus to remove carbon dioxide from the atmosphere, in a process known as carbon fixation. This shift could have major implications for how well the polar oceans remove CO2 from the atmosphere at different times of year. Could autumnal months in the poles show dramatically decreased carbon fixation rates? What would such a pattern mean for current global carbon models? Further research must be conducted at the poles themselves to determine whether this relationship exists in nature, and how it is affecting carbon flux within the polar oceans.

This research was conducted in the lab of Dr. Peter Lee from the College of Charleston at the Hollings Marine Laboratory in collaboration with the Medical University of South Carolina. Many thanks to all members of the lab, particularly Nicole Schanke, MSc.

Stressing Out My Algae

Emily Spiegel, Bryn Mawr College

Emily Carboy 170612

One intern’s perspective on lab work, South Carolina, and the coolest organisms in and out of water: phytoplankton.

 

The lab itself is large, packed to bursting with equipment, boxes, cabinets, monitors, and glassware. An antechamber acts as a sterile room for the most delicate of procedures, demanding precision and care. Many things reside in this room, but never quiet. The constant whirling of a machine’s fan, the hum of a freezer housing samples from a time beyond easy recollection, the typing of a research assistant hunched over innumerable data sheets…all these and more cut through the quiet throughout all hours of the day and night.

 

And at the heart of it all is the algae.

 

Small, marine microorganisms constituting a larger class known as phytoplankton, algae are the unsung heros of the environmental world. Energy, or the basic ability to do work, is the key to survival, growth, and reproduction. Without it you (and your genes) aren’t going anywhere. Algae harness the energy readily available from sunlight and convert it into a useable currency in a process known as primary production. This energy is then distributed to the many higher animals that eat them. They are the foundation of the marine food web and of the world’s energy supply, contributing to 45% of the planet’s primary production (Brierley 2017). In short, algae are cool.

So cool in fact, I’ve decided to spend my entire summer studying them. More specifically, I’ll be studying patterns of their reproduction and growth. A grad student running an experiment in this lab last year got unexpected results when she raised algae in 24 hours of continuous light instead of the normal 12 hours of light:12 hours of darkness she had followed previously.  Despite a limitation in the nitrogen added to these samples, which typically inhibits growth, the populations grown in 24 hours of light were able to grow successfully. So researchers went looking for answers.

One potential explanation is that the continuous light conditions caused the induction of sexual reproduction in the algae samples. Algae, like the rest of us, don’t like to be stressed. And being constantly exposed to light, which they automatically begin to utilize for primary production, is very stressful. It’s kind of like giving a kid a bunch of candy bars. A little is nice, a lot induces a sugar high and headaches for anyone within a 20m radius. The algae have too much energy and so they start to adjust their behavior to accommodate for the stressful conditions. One accommodation is sex. That’s right, stress out your algae and they might just turn on the Marvin Gaye and set the mood. Normally the species I’m studying (Fragilariopsis cylindrus, or just Frag for anyone without a PhD) reproduces asexually allowing high growth rates within the population. My lab is also curious as to whether low light conditions (a cycle of 6 hours of light and 18 hours of darkness) might be equally stressful to the algae and cause a similar response.

This is where I come in. This summer I’ll be exposing algae to conditions of varying light and nutrient stress in order to determine if stress actually does cause them to start reproducing sexually. Along the way, we’ll keep track of growth rates by measuring biomass, or the amount of live material within a sample. This can be measured by a variety of cool devices which tell me the number of cells in a particular volume of sample and the amount of chlorophyll being utilized in that sample. Chlorophyll is a component of the cycle of photosynthesis and is therefore a measure of the primary producers (i.e. the algae) in the sample. Eventually I’ll also run genetic analyses, tracking the utilization of genes involved in sexual reproduction as a way to determine if the algae are reproducing sexually instead of asexually.

All in all, it’s bound to be an interesting summer. Full of days at the beach, early mornings with a culture counter, and lots and lots of algae.

 

I’d like to acknowledge the entire DiTullio/Lee lab at the National Oceanographic and Atmospheric Administration as well as the National Science Foundation’s Research Experiences for Undergraduates program organized by the College of Charleston Grice Marine Laboratory. This project would not be possible without the support and guidance from these institutions and individuals. 

 

Works Cited

Brierley, Andrew. “Plankton.” Current Biology Magazine 27 (2017): 478-83.

To B12 or not to B12, that is the question…

Bryce Penta, University of Notre Dame

As the summer draws to an end, so too does this segment of my research with phytoplankton and vitamin B12. After completing three separate experiments, my project has finally reached its end.

One experimental design encompassed the first two experiments and used a mixed community of phytoplankton straight from the ocean while aboard the R/V Savannah, while the other relied on a culture of Phaeodactylum tricornutum, a phytoplankton species, that had all bacteria removed in laboratory settings. The first pair of experiments were conducted with an addition of both vitamin B12 and nitrate and the final experiment implemented a limitation of the same two nutrients. I specifically looked at the effect of varying availability of these nutrients on the photosynthetic efficiency and growth of the cultures.

IMG_5851

Photo confirming the lack of bacteria in the phytoplankton cultures in lab. The picture also shows that the cultures contained two body forms of Phaeodactylum tricornutum. Photo credit: Lena Pound

This study proposed that an increase in the availability of these nutrients would lead to an increase in efficiency and growth, as well as a decrease leading to a lower efficiency and growth. While we expected an effect of vitamin B12 on the phytoplankton functioning, in all three experiments B12 lacked any significant effect; however, nitrate showed a strong effect on the photosynthetic efficiency and growth in all experiments except the deep sea boat experiment.

While only nitrate exhibited a significant effect on the phytoplankton, this could be due to an alternate metabolic pathway that can bypass the need for vitamin B12. Using methionine synthase E (MetE) rather than the more efficient methionine synthase H (MetH) that requires vitamin B12, the Phaeodactylum tricornutum cultures functioned properly in the absence of vitamin B12 (Helliwell et al. 2011). Unlike the laboratory experiment, the ocean experiments may have lacked a B12 response due to microbes in the water already producing more than enough of the nutrient. Vitamin B12 lacked significant response in our experiments, but other experiments with species that lack the MetE synthase that allows for proper functioning without vitamin B12. Possible B12 effects on phytoplankton could lead to better climate modeling as phytoplankton form the basis of one of the world’s largest ecosystems.

These past ten weeks have culminated in a project that I am proud to have worked on this summer. Though my time here has ended, the people I have met here and the relationships formed over the summer will continue on in the future.

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Lee lab on the R/V Savannah showing off the catch of the trip, a 55 inch wahoo. Photo credit: Bryce Penta

Acknowledgements

This project is possible due to funding from the NSF College of Charleston Summer REU program and the Grice Marine Laboratory. Project ideation and collaboration with Dr. Peter Lee and the Di Tullio lab from the College of Charleston. Lab space and facilities provided by the Hollings Marine Laboratory.

References

Helliwell, K.E., Wheeler, G.L., Leptos, K.C., Goldstein, R.E., Smith, A.G. (2011) Insights into the Evolution of Vitamin B12 Auxotrophy from Sequenced Algal Communities. Molecular Biology and Evolution 28 (10): 2921-2933.

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