AUTHOR=Thorgersen Michael P. , Lancaster W. Andrew , Ge Xiaoxuan , Zane Grant M. , Wetmore Kelly M. , Vaccaro Brian J. , Poole Farris L. , Younkin Adam D. , Deutschbauer Adam M. , Arkin Adam P. , Wall Judy D. , Adams Michael W. W. 

TITLE=Mechanisms of Chromium and Uranium Toxicity in Pseudomonas stutzeri RCH2 Grown under Anaerobic Nitrate-Reducing Conditions

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.01529

DOI=10.3389/fmicb.2017.01529

ISSN=1664-302X

ABSTRACT=<p>Chromium and uranium are highly toxic metals that contaminate many natural environments. We investigated their mechanisms of toxicity under anaerobic conditions using nitrate-reducing <italic>Pseudomonas stutzeri</italic> RCH2, which was originally isolated from a chromium-contaminated aquifer. A random barcode transposon site sequencing library of RCH2 was grown in the presence of the chromate oxyanion (Cr[VI]<inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>O</mml:mtext></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>−</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula>) or uranyl oxycation (U[VI]<inline-formula><mml:math id="M2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>O</mml:mtext></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula>). Strains lacking genes required for a functional nitrate reductase had decreased fitness as both metals interacted with heme-containing enzymes required for the later steps in the denitrification pathway after nitrate is reduced to nitrite. Cr[VI]-resistance also required genes in the homologous recombination and nucleotide excision DNA repair pathways, showing that DNA is a target of Cr[VI] even under anaerobic conditions. The reduced thiol pool was also identified as a target of Cr[VI] toxicity and <italic>psest_2088</italic>, a gene of previously unknown function, was shown to have a role in the reduction of sulfite to sulfide. U[VI] resistance mechanisms involved exopolysaccharide synthesis and the universal stress protein UspA. As the first genome-wide fitness analysis of Cr[VI] and U[VI] toxicity under anaerobic conditions, this study provides new insight into the impact of Cr[VI] and U[VI] on an environmental isolate from a chromium contaminated site, as well as into the role of a ubiquitous protein, Psest_2088.</p>