Insights Into The Genome Of Large Sulfur Bacteria Revealed By Analysis Of Single Filaments

In 1888, Winogradsky proposed the concept of chemolithotrophy-growth using
inorganic compounds as an energy source- after studying the sulfur
bacterium Beggiatoa. These filamentous bacteria and related organisms
inhabit the surface of marine and freshwater sediments, where they oxidize
hydrogen sulfide using either oxygen or nitrate. In particular,
conspicuously large marine representatives accumulate nitrate in vacuoles
to survive
anoxia, a unique feature among prokaryotes.

In a new study published this
week in the open-access journal PLoS Biology, Marc Mussman, Garth Ehrlich,
and colleagues shed new light on these bacteria. Since nitrate-storing
Beggiatoa are not available in pure culture, the researchers amplified and
sequenced the genomic DNA of single multicellular filaments. They
comprehensively tested the incomplete sequence assemblies for non-target
DNA and
show that the Beggiatoa genome encodes the pathways of
chemolithoautotrophy, but also appears to support the use of alternative
electron donors and
acceptors. The researchers propose that vacuolar-type ATPases generate an
electrochemical gradient to drive nitrate transport over the vacuole
membrane, a mechanism similar to eukaryotic solute accumulation.
Intriguingly, they found evidence for substantial gene exchange between
Beggiatoa and
cyanobacteria. In both phyla, hemagglutinins are possibly involved in
filament formation. The breadth of storage and metabolic capabilities
encoded in
its genome enables Beggiatoa to act as a "rechargeable battery," which
glides between oxic and sulfidic zones to overcome non-overlapping
availabilities of electron donors and acceptors.



Citation: MuГџmann M, Hu FZ, Richter M, de Beer D, Preisler A, et al.
(2007) Insights into the genome of large sulfur bacteria revealed by
analysis of
single filaments. PLoS Biol 5(9): e230. doi:10.1371/journal.pbio.0050230.

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