Publication Date:
2019-02-25
Description:
Large, colorless sulfur-oxidizing bacteria (LSB) of the family Beggiatoaceae form thick
mats at sulfidic sediment surfaces, where they efficiently detoxify sulfide before it
enters the water column. The genus Thiomargarita harbors the largest known freeliving
bacteria with cell sizes of up to 750 mm in diameter. In addition to their ability
to oxidize reduced sulfur compounds, some Thiomargarita spp. are known to store
large amounts of nitrate, phosphate and elemental sulfur internally. To date little is
known about their energy yielding metabolic pathways, and how these pathways
compare to other Beggiatoaceae. Here, we present a draft single-cell genome of a
chain-forming “Candidatus Thiomargarita nelsonii Thio36”, and conduct a comparative
analysis to five draft and one full genome of other members of the Beggiatoaceae. “Ca.
T. nelsonii Thio36” is able to respire nitrate to both ammonium and dinitrogen, which
allows them to flexibly respond to environmental changes. Genes for sulfur oxidation
and inorganic carbon fixation confirmed that “Ca. T. nelsonii Thio36” can function as
a chemolithoautotroph. Carbon can be fixed via the Calvin–Benson–Bassham cycle,
which is common among the Beggiatoaceae. In addition we found key genes of
the reductive tricarboxylic acid cycle that point toward an alternative CO2 fixation
pathway. Surprisingly, “Ca. T. nelsonii Thio36” also encodes key genes of the C2-
cycle that convert 2-phosphoglycolate to 3-phosphoglycerate during photorespiration
in higher plants and cyanobacteria. Moreover, we identified a novel trait of a flavin-based
energy bifurcation pathway coupled to a NaC-translocating membrane complex (Rnf).
The coupling of these pathways may be key to surviving long periods of anoxia. As
other Beggiatoaceae “Ca. T. nelsonii Thio36” encodes many genes similar to those
of (filamentous) cyanobacteria. In summary, the genome of “Ca. T. nelsonii Thio36”
provides additional insight into the ecology of giant sulfur-oxidizing bacteria, and reveals
unique genomic features for the Thiomargarita lineage within the Beggiatoaceae.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
peerRev
Format:
application/pdf
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