13 research outputs found
Mechanisms of direct inhibition of the respiratory sulfate-reduction pathway by (per)chlorate and nitrate.
We investigated perchlorate (ClO(4)(-)) and chlorate (ClO(3)(-)) (collectively (per)chlorate) in comparison with nitrate as potential inhibitors of sulfide (H(2)S) production by mesophilic sulfate-reducing microorganisms (SRMs). We demonstrate the specificity and potency of (per)chlorate as direct SRM inhibitors in both pure cultures and undefined sulfidogenic communities. We demonstrate that (per)chlorate and nitrate are antagonistic inhibitors and resistance is cross-inducible implying that these compounds share at least one common mechanism of resistance. Using tagged-transposon pools we identified genes responsible for sensitivity and resistance in Desulfovibrio alaskensis G20. We found that mutants in Dde_2702 (Rex), a repressor of the central sulfate-reduction pathway were resistant to both (per)chlorate and nitrate. In general, Rex derepresses its regulon in response to increasing intracellular NADH:NAD(+) ratios. In cells in which respiratory sulfate reduction is inhibited, NADH:NAD(+) ratios should increase leading to derepression of the sulfate-reduction pathway. In support of this, in (per)chlorate or nitrate-stressed wild-type G20 we observed higher NADH:NAD(+) ratios, increased transcripts and increased peptide counts for genes in the core Rex regulon. We conclude that one mode of (per)chlorate and nitrate toxicity is as direct inhibitors of the central sulfate-reduction pathway. Our results demonstrate that (per)chlorate are more potent inhibitors than nitrate in both pure cultures and communities, implying that they represent an attractive alternative for controlling sulfidogenesis in industrial ecosystems. Of these, perchlorate offers better application logistics because of its inhibitory potency, solubility, relative chemical stability, low affinity for mineral cations and high mobility in environmental systems
Monofluorophosphate Is a Selective Inhibitor of Respiratory Sulfate-Reducing Microorganisms
Despite
the environmental and economic cost of microbial sulfidogenesis
in industrial operations, few compounds are known as selective inhibitors
of respiratory sulfate reducing microorganisms (SRM), and no study
has systematically and quantitatively evaluated the selectivity and
potency of SRM inhibitors. Using general, high-throughput assays to
quantitatively evaluate inhibitor potency and selectivity in a model
sulfate-reducing microbial ecosystem as well as inhibitor specificity
for the sulfate reduction pathway in a model SRM, we screened a panel
of inorganic oxyanions. We identified several SRM selective inhibitors
including selenate, selenite, tellurate, tellurite, nitrate, nitrite,
perchlorate, chlorate, monofluorophosphate, vanadate, molydate, and
tungstate. Monofluorophosphate (MFP) was not known previously as a
selective SRM inhibitor, but has promising characteristics including
low toxicity to eukaryotic organisms, high stability at circumneutral
pH, utility as an abiotic corrosion inhibitor, and low cost. MFP remains
a potent inhibitor of SRM growing by fermentation, and MFP is tolerated
by nitrate and perchlorate reducing microorganisms. For SRM inhibition,
MFP is synergistic with nitrite and chlorite, and could enhance the
efficacy of nitrate or perchlorate treatments. Finally, MFP inhibition
is multifaceted. Both inhibition of the central sulfate reduction
pathway and release of cytoplasmic fluoride ion are implicated in
the mechanism of MFP toxicity