Proteogenomic and functional analysis of chromate reduction in Acidiphilium cryptum JF-5, an Fe(III)-respiring acidophile

Acidiphilium cryptum JF-5, an acidophilic iron-respiring Alphaproteobacterium, has the ability to reduce chromate under aerobic and anaerobic conditions, making it an intriguing and useful model organism for the study of extremophilic bacteria in bioremediation applications. Genome sequence annotati...

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Bibliographic Details
Published in:Biometals 2010-12, Vol.23 (6), p.1129-1138
Main Authors: Magnuson, Timothy S, Swenson, Michael W, Paszczynski, Andrzej J, Deobald, Lee A, Kerk, David, Cummings, David E
Format: Article
Language:eng ; dut
Subjects:
Acidiphilium - genetics
Acidiphilium - metabolism
Acids
Amino Acid Sequence
Bacteria
Chromates
Chromates - metabolism
Chromium
Culture
Cytochromes
Cytochromes c - genetics
Cytochromes c - metabolism
Environmental cleanup
Genomics
Mathematical models
Models, Molecular
Molecular Sequence Data
Oxidation-Reduction
Oxidoreductases - genetics
Oxidoreductases - metabolism
Reductases
Reduction
Sequence Alignment
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Summary:Acidiphilium cryptum JF-5, an acidophilic iron-respiring Alphaproteobacterium, has the ability to reduce chromate under aerobic and anaerobic conditions, making it an intriguing and useful model organism for the study of extremophilic bacteria in bioremediation applications. Genome sequence annotation suggested two potential mechanisms of Cr(VI) reduction, namely, a number of c-type cytochromes, and a predicted NADPH-dependent Cr(VI) reductase. In laboratory studies using pure cultures of JF-5, an NADPH-dependent chromate reductase activity was detected primarily in soluble protein fractions, and a periplasmic c-type cytochrome (ApcA) was also present, representing two potential means of Cr(VI) reduction. Upon further examination, it was determined that the NADPH-dependent activity was not specific for Cr(VI), and the predicted proteins were not detected in Cr(VI)-grown cultures. Proteomic data did show measureable amounts of ApcA in cells grown with Cr(VI). Purified ApcA is reducible by menadiol, and in turn can reduce Cr(VI), suggesting a means to obtain electrons from the respiratory chain and divert them to Cr(VI). Electrochemical measurements confirm that Cr reduction by ApcA is pH dependent, with low pH being favored. Homology modeling of ApcA and comparison to a known Cr(VI)-reducing c-type cytochrome structure revealed basic amino acids which could interact with chromate ion. From these studies, it can be concluded that A. cryptum has the physiologic and genomic capability to reduce Cr(VI) to the less toxic Cr(III). However, the expected chromate reductase mechanism may not be the primary means of Cr(VI) reduction in this organism.
ISSN:0966-0844
1572-8773
DOI:10.1007/s10534-010-9360-y