School of Biological Sciences

Salt marshes cover much of the state of Georgia’s coast and perform key "ecosystem services” for people. They clean the water, protect coastlines against storm surges, and provide a habitat for fish and shellfish. A new study finds that a species of grass that dominates those marshes has bacteria in its roots and surrounding soil that affects productivity by providing nutrients, highlighting the importance of soil microorganisms in the entire ecosystem.

The study, “The core root microbiome of Spartina alterniflora is predominated by sulfur-oxidizing and sulfate-reducing bacteria in Georgia saltmarshes, USA” is published in Microbiome. The research team includes Georgia Tech Ph.D. students Jose Rolando (the study’s lead author) and Tianze Song; Max Kolton, a former postdoctoral researcher, now senior lecturer and principal investigator with Ben-Gurion University of the Negev in Beer Sheva, Israel; and corresponding author Joel Kostka, professor and associate chair for Research in the School of Biological Sciences with a joint appointment in the School of Earth and Atmospheric Sciences, who is also a member of Georgia Tech’s Center for Microbial Dynamics and Infection.

The study shows that diverse and abundant microbes associated with spartina cordgrass help mineralize sediment organic matter and release bioavailable nutrients to the plant, suggesting that the microbes help support plant productivity.

The work could assist efforts to restore salt marshes that will help to strengthen the coastline to be more resilient in the face of sea level rise and climate change.

Kostka says about 40% of salt marshes have disappeared in the U.S. over the past 100 years. “So coastal ecosystem restoration has become a huge field, with an important goal to manage or restore marshes so that they continue to provide critical ecosystem services to people,” he explains.

Kostka adds that certain bacteria benefit plants not only by removing potentially toxic sulfide from the root zone, but also by giving the plant nutrients and potentially carbon. “In other words, this is an example of how we think the classic lines might be blurred by what we generally think of as autotrophs (plants that grow via photosynthesis) and heterotrophs (microbes) in ecosystems.”

Sulfur in the roots

The study was conducted at salt marshes near Sapelo and Skidaway Islands on the Georgia coast in 2018 and 2019. There, ocean water washes over the salt marsh grasses, and that water is rich in sulfate. “Sulfide is a phytotoxin or plant toxin,” Kostka says. “A lot of sulfide will kill plants or at least stress them out, but when you add just a little bit (to Spartina alterniflora), it fuels microbial factories in the plant roots.”

Kostka’s team found that Spartina alterniflora has concentrated sulfur bacteria in its roots, and those bacteria are in two categories: sulfur oxidizers, which use sulfide as an energy source — “then you have sulfate reducers which breathe or respire sulfate from seawater, producing sulfide.”

In this microbial cell factory, bacteria are using sulfide as an energy source to fix nitrogen — and possibly carbon — which then is passed to the grasses. Nitrogen fixation happens when a microbe takes nitrogen gas from air or water and makes usable ammonium out of it. In nature, soil microbes primarily perform this process — occasionally lightning in the atmosphere can also spark it.

The study’s findings suggest that fixation is happening via chemoautotrophy (using chemical reactions for energy) by bacteria living inside the plant roots.

“The next chapter of this story is to learn how the plant and bacteria exchange nitrogen and the environmental controls of that exchange,” Kostka says. “We also know these bacteria can fix carbon, and could potentially be passing carbon to the plant. The plant may have a cell factory that’s making biomass from chemical energy rather than photosynthesis.”

Finding climate clues in plants

The new study’s research in salty wetlands is similar to climate-related work Kostka leads on peat mosses in freshwater bogs at the Spruce and Peatland Responses Under Changing Environments (SPRUCE) research facility in northern Minnesota. The facility is managed by the U.S. Department of Agriculture’s Forest Service and the Oak Ridge National Laboratory.

A study Kostka and his team published in 2021 showed that warming peat bogs are releasing higher amounts of the greenhouse gas methane that is trapped inside them. Peatlands comprise just about 3% of the Earth’s landmass, but they store around one-third of the planet’s soil carbon. As they warm, bogs may also start releasing more carbon along with their methane into ecosystems, a harmful one-two punch for the environment.

The saltwater marshes that Kostka’s team studies have also been termed “blue carbon” sinks because they act to mitigate climate change by sequestering large amounts of carbon from the atmosphere on a global scale. “Salt marshes or coastal marshes are not only critical as habitat for fish and shellfish that we like to eat — along with other vegetated coastal ecosystems — they store as much or more carbon as the remainder of the seafloor,” Kostka says.

A triumph for omics, and what’s next

Kostka credits ‘omics’, technologies which allow for the study of microbes in the environment without cultivation, for advances in uncovering microbiomes — all the microorganisms in a specific environment. Metagenomics and metatranscriptomics, the sequencing of all genes or expressed genes in the environment, allows scientists to chart the potential for microbes to carry out important ecosystem functions like nitrogen fixation. This is critical since very few microbes out of the large diversity that is out there can be grown in the lab, Kostka explains.

“The work is another example of how we are uncovering plant microbiomes — the microbes that live inside or on the tissues of environmentally relevant plants that help the plants to grow better,” Kostka adds. “If we can add microbes to the roots when we plant them, and therefore increase the survival of those plants, we can improve restoration efforts.”

This work was supported in part by an institutional grant (NA18OAR4170084) to the Georgia Sea Grant College Program from the National Sea Grant Office, National Oceanic and Atmospheric Administration, US Department of Commerce, and by a grant from the National Science Foundation (DEB 1754756).

Citation: Rolando, J.L., Kolton, M., Song, T. et al. The core root microbiome of Spartina alterniflora predominated by sulfur-oxidizing and sulfate-reducing bacteria in Georgia salt marshes, USA. Microbiome 10, 37 (2022). https://doi.org/10.1186/s40168-021-01187-7

About Georgia Institute of Technology

The Georgia Institute of Technology, or Georgia Tech, is a top 10 public research university developing leaders who advance technology and improve the human condition. The Institute offers business, computing, design, engineering, liberal arts, and sciences degrees. Its nearly 44,000 students representing 50 states and 149 countries, study at the main campus in Atlanta, at campuses in France and China, and through distance and online learning. As a leading technological university, Georgia Tech is an engine of economic development for Georgia, the Southeast, and the nation, conducting more than $1 billion in research annually for government, industry, and society.

From the science of crafting to a science improv show, Georgia Tech has partnered with the Atlanta Science Festival in filling the month of March with science outreach events since the annual festival was founded in 2014. And after receiving a seed grant from the Dana Foundation for the second year in a row, Christina Ragan is ready to partner with the festival to host her outreach “Super Bowl” — Brain Awareness Day.

With a passion for inspiring others and making neuroscience more accessible, Ragan, a faculty member and lecturer in the School of Biological Sciences and the director of Outreach for the Undergraduate Program in Neuroscience at Tech, is a leader in developing neuroscience-related outreach events.

For the past two years, Ragan has been annually awarded a $1,500 seed grant from the Dana Foundation to design that kind of outreach in celebration of Brain Awareness Week, the Foundation’s global campaign dedicated to fostering curiosity and enthusiasm for brain science.

Arriving at Georgia Tech in early 2021, Ragan organized a virtual Brain Awareness Day event for middle school students that welcomed over 100 attendees.

Everyone is Welcome: Science & Engineering Day at GT 2022

This spring’s programming, scheduled on campus for March 19 as part of Science & Engineering Day at GT, is set have an even bigger audience. (Organizers have confirmed that anyone who missed the RSVP period for this day-long celebration is still welcome to attend without registration, with limited courtesy parking available in the central lot shown here.)

As the 2020 Carol Ann Paul Neuroscience Educator of the Year, Ragan’s dedication in the space has already made an impact on campus. This month, we spoke with Ragan to learn more about Brain Awareness Day and her approach to reaching community members beyond campus:

Q: What is Brain Awareness Week, and why do you think it’s important?

A: Brain Awareness Week, organized by the Dana Foundation, is a great way to share Neuroscience to the public in a way that is engaging, fun, and accessible to a broad audience. We are celebrating Brain Awareness Week in three ways: 1. Our Brain Awareness Day event as part of the Atlanta Science Festival (March 19 from 10am-2pm in CULC 483 and 487), 2. Laboratory Tours for High Schoolers during the March 19 event, and 3. Visiting the Drew School on April 1. My organizing committee of Neuro undergraduates (Rommi Kashlan, Brenna Cheney, Claire Deng, and Payton McClarity-Jones) have been extremely helpful in planning these activities.

I love that we get to involve our undergraduates for our outreach events, so they get to teach others all about the brain. I think it's important for the public to learn about the nervous system since it plays such a critical role in pretty much everything we do. Even when we are asleep or daydreaming, our brain is hard at work.

Science doesn't need to be restricted to folks who have formal degrees. Every time a kid asks, "but why?" they are acting just like a scientist!

Q: Seed grants are often given to help researchers or faculty begin to develop new projects or programs. What project or program do you hope to develop with this grant?

A: I would love to get involved with folks involved in STEM education in the greater Atlanta area to assess the outcomes of events like these. Who are we reaching and who do we still need to increase our efforts to? How can we reach the most people? What kinds of events not only promote students to pursue STEM careers, but also encourage appreciation and literacy for science for those who aren't in STEM fields? I'd also like to form strong relationships with area schools so we can share our Neuroscience demonstrations with them, as well.

This is the second year I have received this grant and I am so excited that we can use it to increase the number of resources we can use for Neuroscience outreach. It is a tremendous honor to be recognized for something I consider so rewarding.

I would love it if attendees for our Atlanta Science Festival event walk away excited, inspired, and curious about Neuroscience. I hope that this year's attendees become regular attendees annually and spread the word to their friends. I would love for attendees to tell their parents and teachers about it so we can arrange more school visits, especially to schools who may not always get opportunities

Q: Where does your passion for neuroscience outreach stem from?

A: My mom introduced me to community outreach at a young age through various volunteering opportunities. She instilled an appreciation, rather than an obligation, for serving others and I have her to thank for promoting that. I always had fun volunteering, especially as a family, and never found it to be a chore.

It wasn’t until graduate school when I became involved in Graduate Women in Science that I started doing STEM outreach. During my Postdoctoral Fellowship at Michigan State University, I was involved with the Neuroscience Fair and school visits for Brain Awareness Week. At Purdue University Northwest, I organized my very own Neuroscience Fair event that hosted 500 attendees.

Q: What’s your favorite neuroscience outreach event or program that you’ve done?

A: I call Brain Awareness Day (the event that will be part of Atlanta Science Festival this year) my “Super Bowl”. I love seeing all the attendees engaged with the presenters and the look on their faces when they learn the neuroscience behind the activity. It's really funny when their minds are just blown away after the gears start turning and they figure something out.

Q: Why do you think this kind of outreach is important?

A: Neuroscience outreach is important, especially for middle school girls, because that is the time in their lives when they are unfortunately taught that being smart or liking science isn't for girls. I don't expect everyone who attends our outreach events to become scientists, but I do aim to encourage an appreciation for science and to think like scientists.

We are truly in the Information Age, and it is our job as educators to help students learn how to evaluate all this information that is literally at their fingertips.

Q: How do you envision outreach playing into the future of Georgia Tech’s Neuroscience program as it continues to develop?

A: I think outreach can have a positive impact for our Tech students and for the community. I envision outreach being something that our program is known for to provide our students an opportunity to engage with the public in a way that is fun and an application of what they have learned in their classes.

I think that what we offer students in the classroom is just a small portion of their education. I would love to foster relationships with other schools and youth organizations to make neuroscience accessible to all.