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Mechanism of chromate reduction by the Escherichia coli protein, NfsA, and the role of different chromate reductases in minimizing oxidative stress during chromate reduction
Author(s) -
Ackerley D. F.,
Gonzalez C. F.,
Keyhan M.,
Blake R.,
Matin A.
Publication year - 2004
Publication title -
environmental microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.954
H-Index - 188
eISSN - 1462-2920
pISSN - 1462-2912
DOI - 10.1111/j.1462-2920.2004.00639.x
Subject(s) - chromate conversion coating , electron transfer , reactive oxygen species , escherichia coli , redox , flavin group , biology , biochemistry , chemistry , enzyme , chromium , inorganic chemistry , photochemistry , organic chemistry , gene
Summary Chromate [Cr(VI)] is a serious environmental pollutant, which is amenable to bacterial bioremediation. NfsA, the major oxygen‐insensitive nitroreductase of Escherichia coli , is a flavoprotein that is able to reduce chromate to less soluble and less toxic Cr(III). We show that this process involves single‐electron transfer, giving rise to a flavin semiquinone form of NfsA and Cr(V) as intermediates, which redox cycle, generating more reactive oxygen species (ROS) than a divalent chromate reducer, YieF. However, NfsA generates less ROS than a known one‐electron chromate reducer, lipoyl dehydrogenase (LpDH), suggesting that NfsA employs a mixture of uni‐ and di‐valent electron transfer steps. The presence of YieF, ChrR (another chromate reductase we previously characterized), or NfsA in an LpDH‐catalysed chromate reduction reaction decreased ROS generation by c . 65, 40, or 20%, respectively, suggesting that these enzymes can pre‐empt ROS generation by LpDH. We previously showed that ChrR protects Pseudomonas putida against chromate toxicity; here we show that NfsA or YieF overproduction can also increase the tolerance of E. coli to this compound.