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2014 ; 14
(ä): 153
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The oxygen sensor MgFnr controls magnetite biomineralization by regulation of
denitrification in Magnetospirillum gryphiswaldense
#MMPMID24915802
Li Y
; Sabaty M
; Borg S
; Silva KT
; Pignol D
; Schüler D
BMC Microbiol
2014[Jun]; 14
(ä): 153
PMID24915802
show ga
BACKGROUND: Magnetotactic bacteria are capable of synthesizing magnetosomes only
under oxygen-limited conditions. However, the mechanism of the aerobic repression
on magnetite biomineralization has remained unknown. In Escherichia coli and
other bacteria, Fnr (fumarate and nitrate reduction regulator) proteins are known
to be involved in controlling the switch between microaerobic and aerobic
metabolism. Here, we report on an Fnr-like protein (MgFnr) and its role in growth
metabolism and magnetite biomineralization in the alphaproteobacterium
Magnetospirillum gryphiswaldense. RESULTS: Deletion of Mgfnr not only resulted in
decreased N2 production due to reduced N2O reductase activity, but also impaired
magnetite biomineralization under microaerobic conditions in the presence of
nitrate. Overexpression of MgFnr in the WT also caused the synthesis of smaller
magnetite particles under anaerobic and microaerobic conditions in the presence
of nitrate. These data suggest that proper expression of MgFnr is required for
WT-like magnetosome synthesis, which is regulated by oxygen. Analyses of
transcriptional gusA reporter fusions revealed that besides showing similar
properties to Fnr proteins reported in other bacteria, MgFnr is involved in the
repression of the expression of denitrification genes nor and nosZ under aerobic
conditions, possibly owing to several unique amino acid residues specific to
MTB-Fnr. CONCLUSIONS: We have identified and thoroughly characterized the first
regulatory protein mediating denitrification growth and magnetite
biomineralization in response to different oxygen conditions in a magnetotactic
bacterium. Our findings reveal that the global oxygen regulator MgFnr is a
genuine O2 sensor. It is involved in controlling expression of denitrification
genes and thereby plays an indirect role in maintaining proper redox conditions
required for magnetite biomineralization.