title: OmcF, a putative c-Type monoheme outer membrane cytochrome required for the expression of other outer membrane cytochromes in Geobacter sulfurreducens.
abstract: Outer membrane cytochromes are often proposed as likely agents for electron transfer to extracellular electron acceptors, such as Fe(III). The omcF gene in the dissimilatory Fe(III)-reducing microorganism Geobacter sulfurreducens is predicted to code for a small outer membrane monoheme c-type cytochrome. An OmcF-deficient strain was constructed, and its ability to reduce and grow on Fe(III) citrate was found to be impaired. Following a prolonged lag phase (150 h), the OmcF-deficient strain developed the ability to grow in Fe(III) citrate medium with doubling times and yields that were ca. 145% and 70% of those of the wild type, respectively. Comparison of the c-type cytochrome contents of outer membrane-enriched fractions prepared from wild-type and OmcF-deficient cultures confirmed the outer membrane association of OmcF and revealed multiple changes in the cytochrome content of the OmcF-deficient strain. These changes included loss of expression of two previously characterized outer membrane cytochromes, OmcB and OmcC, and overexpression of a third previously characterized outer membrane cytochrome, OmcS, during growth on Fe(III) citrate. The omcB and omcC transcripts could not be detected in the OmcF-deficient mutant by either reverse transcriptase PCR or Northern blot analyses. Expression of the omcF gene in trans restored both the capacity of the OmcF-deficient mutant to reduce Fe(III) and wild-type levels of omcB and omcC mRNA and protein. Thus, elimination of OmcF may impair Fe(III) reduction by influencing expression of OmcB, which has previously been demonstrated to play a critical role in Fe(III) reduction.
authors.affiliation: Department of Microbiology, 203 Morrill Science IVN, University of Massachusetts at Amherst, 639 North Pleasant St., Amherst, MA 01003, USA. bckim@microbio.umass.edu
authors.forename: Byoung-Chan
authors.initials: BC
authors.lastname: Kim
authors.forename: Ching
authors.initials: C
authors.lastname: Leang
authors.forename: Yan-Huai R
authors.initials: YH
authors.lastname: Ding
authors.forename: Richard H
authors.initials: RH
authors.lastname: Glaven
authors.forename: Maddalena V
authors.initials: MV
authors.lastname: Coppi
authors.forename: Derek R
authors.initials: DR
authors.lastname: Lovley
mesh_terms: D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000378:metabolism*; D045304:Cytochromes c / Q000235:genetics / Q000378:metabolism*; D005290:Ferric Compounds / Q000378:metabolism; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D045302:Geobacter / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D016415:Sequence Alignment
chemical_list: D001425:Bacterial Outer Membrane Proteins; D005290:Ferric Compounds; C436968:OmcB protein, bacteria; C025314:ferric citrate; D045304:Cytochromes c