All Shrimp Go To Heaven

Carolina Rios, New York University

The Approach: In my previous post, I discussed the negative impact that polychlorinated biphenyls (PCBs), long-lived chemical contaminants, can have on marine ecosystems and human health. Currently, I am working to verify a proposed model to estimate the impact that PCB contamination has on benthic marine invertebrates.

One of the issues with this proposed model is that it is based on data generated from the 1970s; and the analytical methods now available to scientists are much more sensitive and precise. To verify this model, we will generate contemporary data by running a series of short (acute) toxicity tests.

Testing

Test setup for grass shrimp (P. pugio)

In these acute toxicity tests, we measure the response of three species of marine invertebrates to PCBs. The three organisms that we are testing are grass shrimp (Palaemonetes pugio), amphipods (Leptocheirus plumulosus), and mysids (Mysidopsis bahia). We will be measuring mortality from PCB contamination. The standard tests that we are running consists of 6 concentrations, ranging from 6.25 ppb (parts per billion) to 420 ppb. It is important that we also have a control, so that we can understand the response of the organisms unaffected by PCBs. For the grass shrimp and amphipods, the test will run for 96 hours and we will renew the PCB solutions every 24 hours. Samples will be taken for chemical analysis at 0 hours, 24 hours, and 72 hours, so as to measure both the loss of PCBs over the 24 hour period, as well as the consistency of dosing. Loss of PCBs can be attributed to PCBs binding to the glassware and differences in dosing can be attributed to user variability. For the mysids, the test will also run for 96 hours, but the dosing solutions will not be renewed after the initial dosing. Samples will be taken at 0 hours, 48 hours, and 96 hours, so as to measure the loss of PCBs over the 96 hour period. For all tests, mortality will be recorded every 24 hours until the end of the test.

Analysis

Solid Phase Extraction apparatus. Dosed samples are within the large reservoirs at the top of the apparatus. PCBs will be isolated on the nonpolar solid phase, which consists of the smaller columns below the reservoirs.

The PCBs from the collected samples will be isolated through solid phase extraction. Solid phase extraction consists of a nonpolar solid phase and a polar liquid phase; similar to how oil cannot be mixed into vinegar, PCBs are not very soluble in water. As PCBs are nonpolar and hydrophobic, they will bind to the solid phase. The PCBs can then be lifted off of the column by running a nonpolar solvent (ethyl acetate) through the nonpolar solid phase. The sample is then analyzed using gas chromatography-mass spectrometry (GC-MS). The essential concept of GC-MS is that molecules will separate based on differences in size. This is how the amount of each individual PCB is determined, which can then be used to calculate an actual concentration. Analysis of the chromatograph can give more accurate concentrations, allowing us to understand how concentrations vary over time. This will give us a better understanding of the relationship between dose concentrations and the mortality response.

Acknowledgements

I would like to thank Dr. Ed Wirth and Brian Shaddrix for their continued guidance and support, as well as my co-mentor Dr. Paul Pennington. Supported by the Fort Johnson REU Program, NSF DBI-1757899.

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).