In a recent study in BMC Biology, Grace Kenny and Amy Rosenzweig have bioinformatically mined a number of available bacterial genomes (and a few metagenomes) to look for the genes responsible for methanobactin production, thought to be key to methane metabolism by bacteria.
Not many other organisms would fancy eating methane, but some bacteria – termed methanotrophs – do and they have recently been a focus of considerable attention as potential environmental scrubbers: around 10-15 percent of human-generated methane emissions each year are estimated to come from biodegradable materials in landfills, so there is keen interest in ways of mitigating the release of the potent – not to mention flammable – greenhouse gas.
The molecular details of methane metabolism by methanotrophs aren’t known with certainty, but we do know that copper is important, with different enzymes being used when it is abundant compared with when it’s scarce. This ‘copper switch’ involves methanobactins, a class of peptides that scavenge copper from the environment, but beyond this details start to become vague: for example, methanobactins from different bacterial species have significant differences in structure, but similarly strong copper binding activity. Kenney and Rosenzweig’s study is an attempt to shine some light into this gloom.
The results are somewhat surprising. Despite only five of the species investigated being known methanotrophs, fully fourteen of them appear to possess genes that can produce methanobactin-like products. So what does this mean? Rather than suggesting that many bacteria can degrade methane, the most likely explanation is that methanobactins represent only one example of a largely undescribed class of proteins responsible for regulating metal levels in bacteria. Similarly unexpected is the converse finding: some methanotrophic species appear not to possess the genes necessary for methanobactin production. Of course, they must get copper from somewhere, and the authors suggest that this may mean there is yet another class of copper-transporting mechanisms waiting to be discovered – but one also shouldn’t forget that bacteria are regularly found in mixed communities, and they may simply ‘borrow’ exported methanobactins from their neighbours.
There’s a wealth of information in the paper, and experimental validation will be key; but hopefully it’s a significant step to fully understanding, and eventually using, the methane-degrading capacities of bacteria.
Written by Kester Jarvis, Senior Editor for BMC Biology.