SARASOTA, Florida -- Florida researchers are shedding new light on how marine bacteria manage to adapt so rapidly in a study reported in the new edition of Science which shows widespread, horizontal gene transfers allow the organisms to be resilient in the face of environmental change.
The finding is especially significant in efforts to understand how communities of organisms, such as coral reefs, adapt to challenges in the environment, the scientists said.
Gene Transfer Agents (GTAs), viral-like particles produced by α-Proteobacteria, demonstrated activity in the natural environment that had not been previously documented, reports a scientific team lead by University of South Florida and Mote Marine Laboratory researchers. The group documented GTA frequencies 1,600 to 450-million times higher than previous estimates of gene transfer by currently well-known means in the oceans, suggesting it is a mechanism by which marine bacteria acquire some traits in a matter of minutes rather than through thousands of years of evolution.
Scientists have long known higher organisms transfer DNA through reproduction, but until now have had limited understanding of how the most basic organisms – microbes – accomplished the same feat. USF marine microbiologist Lauren McDaniel said the GTA gene transfer mechanism has been observed in the laboratory setting for decades, but until now scientists had not documented that it also exists in nature and is an important mechanism in adaptation.
McDaniel said the bacteria that carry the GTAs are common in reef and coastal environments, making this discovery even more significant for future understanding of the marine environment. The project is funded by the National Science Foundation and Florida's Protect Our Reefs Grant program, which is supported by Florida drivers through the sale of coral reef license plates.
This process is caused by GTAs, minute viral-like "genetic escape pods" that are encoded in certain marine bacterial genomes, said USF Biological Oceanographer and Distinguished Professor John Paul.
By this method, random pieces of the donor cell's DNA are packaged into the GTA particles. The GTA particles are released and act like viruses, "infecting" other bacteria and spreading the donor DNA fragments throughout the microbial community, Paul said.
"The natural evolution of genes is a very slow process taking years to thousands of years, whereas swapping a gene can happen in five minutes," he said. "It's a rapid and random mechanism of environmental adaptation."
The transfer of genes by GTAs was originally observed in the bacteria Rhodobacter capsulatus and this isolate has been studied in a laboratory setting. To understand how it occurs in nature, the research team tested a region adjacent to Looe Key Reef in the Florida Keys National Marine Sanctuary in September 2009 for GTA activity, as well as an area in the Alafia River and in the Gulf of Mexico.
Kim Ritchie, manager of the Marine Microbiology Program at Mote Marine Laboratory and one of the paper's authors, said the study shows a higher level of gene transfer in the reef environment, a finding that potentially could help scientists know whether beneficial genes are being transferred to create healthier coral reefs. "With climate change, organisms are having to adapt to a changing environment — the reef is a microcosm of this," Ritchie said. "It's a very important ecosystem that has to adapt to survive. Maybe there is hope for the future of ocean ecosystems because microbes are able to rapidly adapt by exchanging beneficial genetic material."
In the experiments, natural marine bacterial populations from a range of environments were isolated and briefly incubated with laboratory-produced, genetically marked GTA particles. Gene transfer was monitored by increased levels of resistance to a marker antibiotic as well as verification of gene acquisition by DNA sequencing. In certain experiments gene transfer to nearly half the marine microbial population occurred.
The known methods for horizontal gene transfer in bacteria currently include uptake of naked DNA (transformation), exchange of plasmids (conjugation), and accidental transfer of bacterial DNA by an infecting virus (transduction), the paper reports.
"In the ocean environment, these processes can occur on a global scale," Paul said. "They can drastically alter the environment, the amount of greenhouse gases produced and the amount of CO2 being drawn down. How the environment changes; the adaptation; if there are genetic processes – what we call genetic flexibility and adaptability – then no matter what gets thrown at us there is some genetic mechanism to respond to it."
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