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GlobalRegulatorIscRPositivelyContributestoAntimoniteResistanceandOxidationinComamonastestosteroniS44 (Liu H)

Hongliang Liu 1, 2†, WeipingZhuang1 †, ShengzheZhang1, ChristopherRensing3,
Jun Huang1, JieLi 1 and GejiaoWang1*

Antimonial compounds can be found as a toxic contaminant in the environment.
Mechanisms of microbial Sb oxidation and its role in microbial tolerance are limited.
Previously, we found that Comamonas testosteroni S44 was resistant to multiple
heavy metals and was able to oxidize the toxic antimonite [Sb(III)] to the much less
toxic antimonate [Sb(V)]. In this study, transposon mutagenesis was performed in C.
testosteroni S44 to isolate genes responsible for Sb(III) resistance and oxidation. An
insertion mutation into iscR, which regulates genes involved in the biosynthesis of Fe-
S clusters, generated a strain called iscR-280. This mutant strain was complemented
with a plasmid carrying iscR to generate strain iscR-280C. Compared to the wild type
S44 and iscR-280C, strain iscR-280 showed lower resistance to Sb(III) and a lower Sb(III)
oxidation rate. Strain iscR-280 also showed lower resistance to As(III), Cd(II), Cu(II), and
H2O2. In addition, intracellular γ -glutamylcysteine ligase (γ -GCL) activity and glutathione
(GSH) content were decreased in the mutated strain iscR-280. Real-time RT-PCR and
lacZ fusion expression assay indicated that transcription of iscR and iscS was induced
by Sb(III). Results of electrophoretic mobility shift assay (EMSA) and bacterial one-hybrid
(B1H) system demonstrated a positive interaction between IscR and its promoter region.
The diverse defective phenotypes and various expression patterns suggest a role for
IscR in contributing to multi-metal(loid)s resistance and Sb(III) oxidation via Fe-S cluster
biogenesis and oxidative stress protection. Bacterial Sb(III) oxidation is a detoxification
reaction.

 



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