Fresh stacks of muddy bacteria

Lilia Garcia, Illinois Wesleyan University

The Approach: In my last post, I wrote about Gracilaria, an invasive red seaweed on the coast of South Carolina, and its effect on Vibrio bacteria. My project aims to record the number and strains, or types, of Vibrio growing around Gracilaria and compare it to seaweed-free areas. I will also compare the Vibrio count residing on Gracilaria versus the Vibrio residing on a native seaweed called Ulva to see how an invasive species changes the bacterial community. Lastly, I want to understand how Gracilaria stops the growth of specific Vibrio strains by producing chemical compounds.

Mud samples under Gracilaria, taken by K. Coates

To begin solving my questions, I will go out to collect samples in the mudflats outside of the Grice Laboratory. I will collect tubes of water, clumps of Gracilaria and Ulva, and mud from underneath and 1.5 feet away from Gracilaria. Afterwards, I’ll spread all the samples onto dishes with nutrients specifically used to grow Vibrio. The bacteria grow in spots called colonies, and I will count each spot to see how much Vibrio there is in each sample. I am looking for a different amount of colonies in mud samples collected within or away from Gracilaria patches, and a difference in colony numbers between the Ulva and Gracilaria.

Dishes of unique Vibrio, taken by L. Garcia

A single dish from a mud sample can contain hundreds of colonies, differing in color, shape, size, and texture. Each of these colonies represent a different strain of Vibrio, uncovering the diversity of bacteria at different distances from Gracilaria. I will characterize which unique colonies are dangerous to human health, and whether they are found near or away from Gracilaria.

Zones of inhibition against Vibrio strain, taken by L. Garcia

As previously mentioned, I will also test Vibrio strains against chemical compounds made on the surface of Gracilaria. These compounds are able to control the kind of bacteria that grow around seaweed, changing the microscopic habitat. I will mix Gracilaria with chemicals to remove its surface chemistry, then spot the compounds onto dishes growing Vibrio from my mud samples. I am looking for large clear circles, called zone of inhibitions, that tell me the specific strain of Vibrio cannot grow due to the compound.

Nearly all we know about the ecological and economic impact of Gracilaria focuses on large animals, such as fish. My project zooms in on micro-organisms that have been overlooked. The information I collect will help us understand how invasive Gracilaria is changing bacterial communities not only in the Charleston Harbor, but potentially the entire coast.  Although invisible, bacteria make up the foundation of ecosystems and high Vibrio levels may be dangerous for our health. I look forward to finding the answers to my questions hiding quietly in the mud.

Acknowledgements

Thank you to my mentor Dr. Erik Sotka, and our collaborator Dr. Erin Lipp. I would also like to thank Dr. Alan Strand and Kristy Hill-Spanik for their supporting guidance. Lastly, thank you to Dr. Loralyn Cozy (IWU) for preparing me to succeed in the lab. All research is funded by Grice Marine Lab and College of Charleston through the Fort Johnson REU Program, NSF DBI-1757899

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Invisible Neighbors: How Gracilaria Changes Bacterial Communities

Lilia Garcia, Illinois Wesleyan University

The Problem: It only takes a walk along the mudflats to notice large patches of wiry, red seaweed. The seaweed is called Gracilaria vermiculophylla, an invasive organisms that is native to East Asia (SERC, 2019)  The seaweed is hard to miss, but its effects on the ecosystem are not easily seen. This summer I will be studying how Gracilaria affects a bacterial community invisible to the naked eye.

Mudflat with Gracilaria, taken by L. Garcia

According to previous studies, Gracilaria is found to increase the amount of a bacteria called Vibrio (Gonzalez, et al., 2014). This may not mean much at first, since most of us don’t think about microscopic interactions. Bacteria, however, are important in maintaining the health of complex environments like estuaries. They cycle and break down nutrients and organic matter, influencing oxygen, carbon, and nitrogen levels. An increase in one group of bacteria, such as Vibrio, can change these patterns. And like most of us know, bacteria tends to spread easily. There are a few strains, or types, of Vibrio, such as V. vulnificus, V. parahaemolyticus, and V. cholera, that are dangerous to human health. An increase in these strains may cause an increase in disease from swimming or eating infected food.†

Vibrio growing on petri dish, taken by L. Garcia

We known Vibrio levels increase with Gracilaria, but we do not know how this happens. We also don’t know if all Vibrio strains increase together, or if only a few strains grow. To understanding the relationship between Gracilaria and Vibrio, I will record how much total Vibrio and how many strains of Vibrio grow in and away from patches of Gracilaria. In order to preserve its own health, Gracilaria produces compounds that promote or stop organisms from growing around it (Assaw et al., 2018). These are compounds I will test against different strains to study the mechanism Gracilaria uses affect specific Vibrio levels. I want to see how the growth of each strain is affected by different extracts. Will the strains further away from the Gracilaria be unable to grow when exposed to a certain type of extract? Will other strains grow better with the extract?

We tend to think about invasive species on a large scale, assessing the damage it causes to other familiar animals and plants. The ecosystem relies on tiny, cellular organism and studying how bacteria changes leads to a deeper understanding of environmental health. An invisible community is changing as Gracilaria flourishes, and there is a lot left to learn about it. 

Acknowledgements

Thank you to my mentor Dr. Erik Sotka, and our collaborator Dr. Erin Lipp. I would also like to thank Dr. Alan Strand and Kristy Hill-Spanik for their supporting guidance. Lastly, thank you to Dr. Loralyn Cozy (IWU) for preparing me to succeed in the lab. All research is funded by Grice Marine Lab and College of Charleston through the Fort Johnson REU Program, NSF DBI-1757899

References

Assaw S, Rosli N, Adilah N, Azmi M, Mazlan N, Ismail N. 2018. Antioxidant and Antibacterial Activities of Polysaccharides and Methanolic Crude Extracts of Local Edible Red Seaweed Gracilaria sp. Malays Appl Biol. 47(4): 135-144. 

Fofonoff PW, Ruiz GM, Steves B, Simkanin C, & Carlton JT. 2019. National Exotic Marine and Estuarine Species Information System. 

Gonzalez D, Gonzalez R, Froelich B, Oliver J, Noble R, McGlathery K. 2014. Non-native macroalga may increase concentrations of Vibrio bacteria on intertidal mudflats. Mar Ecol Prog Ser. 505: 29-36.