Coral reefs might be getting a major boost from bacteria that share good genes, report researchers who have found the first evidence that genetic packets from these bacteria help pave the way for "baby" corals to grow.
This ongoing study, being presented today at an international coral conference, is a key advance in understanding the processes underlying coral reef growth and health. Reefs depend on intricate relationships between corals and many marine microscopic life forms, including the symbiotic algae within coral tissues and beneficial bacteria living on and near the reef. Most of these relationships are still being described by researchers.
"Coral reefs around the globe are under threat from climate change, ocean acidification and disease; to help reefs, we need to know much, much more about their basic biology, ecology and relationships with other forms of marine life," said Dr. Kim Ritchie, co-leader of the study and Manager of the Marine Microbiology program at Mote Marine Laboratory in Sarasota, Fla. "All of these things are vital for understanding how corals survive, grow and reproduce."
The current study is a team effort by Mote, the University of South Florida in St. Petersburg and King Abdulla University of Science and Technology (KAUST) in Saudi Arabia. Preliminary results were presented today during the 12th International Coral Reef Symposium in Cairns, Australia (ICRS), which includes participants from about 80 countries and is held every four years to advance scientific knowledge, conservation and management of coral reefs.
Scientists have long known that bacteria - most of which reproduce by splitting rather than sex - are also able to transfer genes from one to another through something called "horizontal gene transfer." One way bacteria do this is by producing particles called "gene transfer agents" (GTAs). In this process, random pieces of a donor bacterium's DNA are packed into GTAs - packets containing pieces of DNA called genes - and released. Once set free, like genetic escape pods, these GTAs act like viruses "infecting" other bacteria and spreading the donor's DNA fragments throughout the microbial community.
Researchers suspect that sharing GTAs could allow bacteria to spread beneficial genes across reefs, possibly helping corals, their resident algae or fellow reef-dwelling bacteria adapt to environmental challenges quickly. Sharing GTAs can take minutes, whereas adapting by traditional evolution can take thousands of years.
Research led by USF and Mote, published in a 2010 issue of Science, showed that widespread marine bacteria called Ruegeria transfer genes to other bacteria at remarkable rates on coral reefs.
In 2011, the researchers set out to test the effects of GTAs on coral offspring, or larvae, in the lab. Working at Mote's Tropical Research Laboratory on Summerland Key, Fla., the researchers investigated whether GTAs from bacteria called Ruegeria helped larvae of mustard hill coral (Porites astreoides) and mountainous star coral (Montastraea faveolata) settle to start growing. The larvae were placed in petri dishes with "biofilms" - clusters of microbes that are believed to help larvae attach to surfaces - and both the larvae and biofilms were treated with GTAs.
"When we added GTAs, the coral larvae were four times more likely to settle, which is a very exciting result," said Ritchie. With GTAs present, about 12 percent of coral larvae settled, compared with only 3 percent without GTAs. Project scientists from Mote and USF have continually replicated these results and this portion of their study is expected to be released this year.
Meanwhile, project scientists at KAUST are working to describe the gene-sharing process in detail. Ruegeria DNA appears to have its strongest effect on the bacteria, algae or other microbes in the biofilm, helping them grow, multiply, produce substances or do other activities that help provide a better "landing pad" for the coral larvae or assist them in settling. KAUST scientists plan to decode the DNA shared by Ruegeria and create a detailed map showing which genes are "turned on" by the GTAs in the organisms receiving them.
"Corals and their associated microbes must be understood as a whole 'metaorganism'; marine microbes are central to coral reef ecology in ways that the research community is just beginning to discover," said Christian R. Voolstra, Assistant Professor of Marine Science at KAUST. "Advancing this frontier is important to us, and we are grateful to collaborate internationally with Mote and USF scientists who are breaking new ground in this important line of reef research."
"What we're learning in the lab could, in time, lead to a new understanding of coral reefs in the ocean," said Dr. John Paul, Distinguished University Professor of Biological Oceanography at USF. "Reefs around the world host a number of bacteria that produce GTAs. By learning what these gene-swapping bacteria might contribute to coral life cycles, we can provide resource managers essential knowledge to protect or even enhance reefs."
This project was funded by the National Science Foundation, the Dart Foundation, the Moore Foundation, KAUST and the Protect Our Reefs grants program, which receives its funds from sales of the Protect Our Reefs specialty license plate administered by Mote and available to Florida drivers. Protect Our Reefs provides crucial support to groundbreaking reef research focused on corals in the Florida Keys, home to the only barrier reef in the continental U.S. Learn more and learn how Florida drivers can purchase the plate at www.mote.org/4reef
Founded in 1955, Mote Marine Laboratory is an independent, nonprofit 501(c)3 research organization based in Sarasota, Fla., with field stations in eastern Sarasota County, Charlotte Harbor and the Florida Keys. Donations to Mote are tax deductible to the fullest extent allowed by law.
Mote is dedicated to today's research for tomorrow's oceans with an emphasis on world-class research relevant to conservation and sustainable use of marine biodiversity, healthy habitats and natural resources. Research programs include studies of human cancer using marine models, the effects of man-made and natural toxins on humans and on the environment, the health of wild fisheries, developing sustainable and successful fish restocking techniques and food production technologies and the development of ocean technology to help us better understand the health of the environment. Mote research programs also focus on understanding the population dynamics of manatees, dolphins, sea turtles, sharks and coral reefs and on conservation and restoration efforts related to these species and ecosystems. Mote's vision includes positively impacting public policy through science-based outreach and education. Showcasing this research is Mote Aquarium, open from 10 a.m. to 5 p.m. 365 days a year. Learn more at www.mote.org