Iodate Reduction by Shewanella oneidensis Does Not Involve Nitrate Reductase. Issue 7 (9th August 2018)

• Record Type: Journal Article
• Authors: Mok, Jung Kee; Toporek, Yael J.; Shin, Hyun-Dong; Lee, Brady D.; Lee, M. Hope; DiChristina, Thomas J.
• Is Part Of: Geomicrobiology journal. Volume 35:Issue 7(2018)
• Page Start: 570
• Page End: 579
• Publication Date: 2018-08-09
• Subjects: Iodate -- nitrate -- reduction -- shewanella oneidensis; Geomicrobiology -- Periodicals; Biogeochemistry -- Periodicals; 579
• DOI: 10.1080/01490451.2018.1430189
• Languages: English
• ISSNs: 0149-0451

Abstract

ABSTRACT: Microbial iodate (IO3 − ) reduction is a major component of iodine biogeochemical cycling and is the basis of alternative strategies for remediation of iodine-contaminated environments. The molecular mechanism of microbial IO3 − reduction, however, is not well understood. In several microorganisms displaying IO3 − and nitrate (NO3 − ) reduction activities, NO3 − reductase is postulated to reduce IO3 − as alternate electron acceptor. In the present study, whole genome analyses of 25 NO3 − -reducing Shewanella strains identified various combinations of genes encoding one assimilatory (cytoplasmic Nas) and three dissimilatory (membrane-associated Nar and periplasmic Napα and Napβ) NO3 − reductases. Shewanella oneidensis was the only Shewanella strain whose genome encoded a single NO3 − reductase (Napβ). Terminal electron acceptor competition experiments in S. oneidensis batch cultures amended with both NO3 − and IO3 − demonstrated that neither NO3 − nor IO3 − reduction activities were competitively inhibited by the presence of the competing electron acceptor. The lack of involvement of S. oneidensis Napβ in IO3 − reduction was confirmed via phenotypic analysis of an in-frame gene deletion mutant lacking napβA (encoding the NO3 − -reducing NapβA catalytic subunit). S. oneidensis Δ napβA was unable to reduce NO3 −, yet reduced IO3 − at rates higher than the wild-type strain. Thus, NapβA is required for dissimilatory NO3 − reduction by S. oneidensis, while neither the assimilatory (Nas) nor dissimilatory (Napα, Napβ, and Nar) NO3 − reductases are required for IO3 − reduction. These findings provide the first genetic evidence that IO3 − reduction by S. oneidensis does not involve nitrate reductase and indicate that S. oneidensis reduces IO3 − via an as yet undiscovered enzymatic mechanism.