The microbes, belonging to a family called Pseudoalteromonas, are found in habitats as wide-ranging as sea grasses and corals.
Experts previously thought the environmentally-unfriendly compounds they produce, known as polybrominated diphenyl ethers (PBDEs), were all man-made. But recent studies have shown levels of the chemicals in animal species suggest a natural as well as artificial source. PBDEs, now subject to bans in Europe and the US, are incorporated into foams, textiles and circuitry to raise the temperature at which products will burn.
Scientists identified a group of 10 genes in Psuedoalteromonas involved in the synthesis of more than 15 bromine-containing compounds including PBDEs. Professor Bradley Moore, from the University of California at San Francisco, who led the research published in the journal Nature Chemical Biology, said: "We find it very surprising and a tad alarming that flame retardant-like chemicals are biologically synthesised by common bacteria in the marine environment."
The scientists now hope to find out precisely how the compounds are getting into the food chain.