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.


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

RXR sequenced, now on to imposex

Samera Mulatu, Georgia Southern University

IMG-0640Findings: My experience at the Fort Johnson REU Program was phenomenal! Towards the end of the program, I was able to retrieve the RXR gene sequences for the Eastern mud snail. While working towards this goal, I was able to get a first hand glimpse of the long and hard steps and techniques taken to retrieve DNA sequences. From generating primers, doing dissections, extracting RNA, making cDNA, and even making PCR products, these listed skills are only just a short list of what I learned during this research experience. Retrieving the RXR gene sequences for the mud snail, was a trial and error process. Sequences were sent in at least five times, and four of those five times did not give good results. This was a big lesson for me, and reminded me that science is a trial and error process because all of it is a learning process.

Now that the RXR gene sequence for the Eastern mud snail was retrieved, the next steps in this project would be to use the sequences to place the mud snail in its proper spot on the phylogenetic tree. Also, now that the gene sequences are retrieved they will be used next fall by Edwina Mathis (a graduate at MUSC who’s doing her research in this topic) and Dr. Demetri Spyropoulos to induce imposex in the Eastern mud snail while exposing the snails to TBT, SPAN 80, and DOSS. Afterwards, they will measure changes in isoform expression.

The significance of the results from this study will hopefully show that mud snail imposex is a sensitive indicator of endocrine disrupting compounds in the environment which may impact human health and the health of other organisms in the ecosystem. This is because high imposex rates in mud snail species could possibly be linked to higher levels of contamination found in that site within the Charleston Harbor. Hopefully this study will further future research on EDCs and their effects on different species.

I would like to give a big thank to Dr. Demetri Spyropoulos for guiding me in my research. Also to the Fort Johnson REU Program, NSF DBI- 1757899, for providing me with the funds to complete this project.

Related research

Hotchkiss, A.K, A.G.Leblanc, R.M. Sternberg. 2002. Synchronized expression of Retinoid X Receptor mRNA with Reproductive Tract Recrudescence in an Imposex- Susceptible Mollusc. Environ. Sci Technol. 42: 1345- 1351.

Ravitchandirane, V. S, M.Thangaraj. 2013. Phylogenetic Status of Babylonia Zeylanica (Family Babyloniidae) Based on 18S rRNA GENE FRAGMENT.Annals of West University of Timisoara, ser. Biology. 1(2): 135- 140.

Barron- Vivanco, B.S, D. Dominguez- Ojeda, I.M. Medina- Diaz, A.E. Rojas- Garcia, M.L. Robledo- Marenco. 2014. Exposure to tributyltin chloride induces penis and vas deferns development and increases RXR expression in females of the purple snail (Plicopurpura pansa). Invertebrate Survival Journal. 11: 204-2012.

Horiguchi, T., M. Morita, T. Nishikawa, Y. Ohta, H. Shiraishi. 2007. Retinoid X Receptor gene expression and protein content in tissues of the rock shell Thais clavigeraAquatic Toxicology. 84: 379-388.