Journal
JOURNAL OF BACTERIOLOGY
Volume 194, Issue 21, Pages 5840-5847Publisher
AMER SOC MICROBIOLOGY
DOI: 10.1128/JB.00890-12
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Funding
- National Science Foundation [EAR 21472-443143]
- University of California, Santa Cruz, Minority Biomedical Research Support Fellowship (MBRS)
- Research Mentoring Institute (RMI) Graduate Diversity Fellowship
- Alliance for Graduate Education and the Professoriate Program (AGEP)
- LDRD project [11-LW-054]
- U.S. Department of Energy by Lawrence Livermore National Laboratory [DEAC52-07NA27344]
- Division Of Earth Sciences
- Directorate For Geosciences [0951947] Funding Source: National Science Foundation
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Extracellular respiration of solid-phase electron acceptors in some microorganisms requires a complex chain of multiheme c-type cytochromes that span the inner and outer membranes. In Shewanella species, MtrA, an similar to 35-kDa periplasmic decaheme c-type cytochrome, is an essential component for extracellular respiration of iron(III). The exact mechanism of electron transport has not yet been resolved, but the arrangement of the polypeptide chain may have a strong influence on the capability of the MtrA cytochrome to transport electrons. The iron hemes of MtrA are bound to its polypeptide chain via proximal (CXXCH) and distal histidine residues. In this study, we show the effects of mutating histidine residues of MtrA to arginine on protein expression and extracellular respiration using Shewanella sp. strain ANA-3 as a model organism. Individual mutations to six out of nine proximal histidines in CXXCH of MtrA led to decreased protein expression. However, distal histidine mutations resulted in various degrees of protein expression. In addition, the effects of histidine mutations on extracellular respiration were tested using ferrihydrite and current production in microbial fuel cells. These results show that proximal histidine mutants were unable to reduce ferrihydrite. Mutations to the distal histidine residues resulted in various degrees of ferrihydrite reduction. These findings indicate that mutations to the proximal histidine residues affect MtrA expression, leading to loss of extracellular respiration ability. In contrast, mutations to the distal histidine residues are less detrimental to protein expression, and extracellular respiration can proceed.
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