Comparative proteomics and activity of a green sulfur bacterium across the water column of Lake Cadagno, Switzerland.

Kirsten Silvia Habicht, Mette Miller, Raymond Pickett Cox, Niels-Ulrik Frigaard, Mauro Tonolla, Sandro Peduzzi, Lasse Gaarde Falkenby, Jens S. Andersen

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Abstrakt

Primary production in the meromictic Lake Cadagno,
Switzerland, is dominated by anoxygenic photosynthesis.
The green sulfur bacterium Chlorobium clathratiforme
is the dominant phototrophic organism in
the lake, comprising more than half of the bacterial
population, and its biomass increases 3.8-fold over
the summer. Cells from four positions in the water
column were used for comparative analysis of the
Chl. clathratiforme proteome in order to investigate
changes in protein composition in response to the
chemical and physical gradient in their environment,
with special focus on how the bacteria survive in the
dark. Although metagenomic data are not available
for Lake Cadagno, proteome analysis was possible
based on the completely sequenced genome of an
isolated strain of Chl. clathratiforme. Using LC-MS/MS
we identified 1321 Chl. clathratiforme proteins in Lake
Cadagno and quantitatively compared 621 of these in
the four samples. Our results showed that compared
with cells obtained from the photic zone, cells
collected from the dark part of the water column had
the same expression level of key enzymes involved in
carbon metabolism and photosynthetic light harvesting.
However, most proteins participating in nitrogen
and sulfur metabolism were twofold less abundant in
the dark. From the proteome analysis we were able to
show that Chl. clathratiforme in the photic zone contains
enzymes for fixation of N2 and the complete
oxidation of sulfide to sulfate while these processes
are probably not active in the dark. Instead we
propose that Chl. clathratiforme cells in the dark part
of the water column obtain energy for maintenance
from the fermentation of polyglucose. Based on the
observed protein compositions we have constructed
possible pathways for C, N and S metabolism in Chl.
clathratiforme.
OriginalsprogEngelsk
TidsskriftEnvironmental Microbiology
Vol/bind13
Udgave nummer1
Sider (fra-til)203-215
ISSN1462-2912
StatusUdgivet - 2011

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