Mobile Electron Carriers

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Science  14 Sep 2007:
Vol. 317, Issue 5844, pp. 1471
DOI: 10.1126/science.317.5844.1471c

Microbes that have not yet been cultured under laboratory conditions are, not surprisingly, rather more difficult to work with than those that have, such as the perennial workhorses Escherichia and Saccharomyces. Nevertheless, recent forays into soil and marine communities have hinted at a wealth of untapped pharmaceutical and biochemical expertise, and technological advances in extracting and sequencing genomic DNA of unpurified (and in many cases, unseen) organisms have begun to bring those microbial skills within reach.

Mußmann et al. have analyzed a single Beggiatoa filament (roughly 30 μm wide and 1 cm long) of almost 1000 cells by whole-genome amplification and pyro(phosphate) sequencing. They have been able to assemble enough sequence to cover approximately ¾ of the 11-Mb genome as estimated by the recovery of single-copy marker genes and aminoacyl tRNA synthetases. The collection of sulfur-, nitrogen-, and oxygen-metabolizing enzymes, albeit still incomplete, provides genetic evidence for the elevatorlike lifestyle of this bacterium, which cycles vertically as it harvests energy from the oxidation of sulfidic deposits. At the relatively oxygen-rich surface of marine sediments, electrons from elemental sulfur are donated to oxygen, yielding sulfate; in deeper, anoxic regions of the sediment, nitrate is recruited as the acceptor of electrons from hydrogen sulfide. Beggiatoa are energetic hoarders of nitrate, accumulating it in vacuoles in concentrations as high as 0.5 M to the dismay of competing denitrifying bacteria. — GJC

PLoS Biol. 5, e230 (2007).

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