Description:
<jats:title>ABSTRACT</jats:title>
<jats:p>
Previous studies failed to detect
<jats:italic>c</jats:italic>
-type cytochromes in
<jats:italic>Pelobacter</jats:italic>
species despite the fact that other close relatives in the
<jats:italic>Geobacteraceae</jats:italic>
, such as
<jats:italic>Geobacter</jats:italic>
and
<jats:italic>Desulfuromonas</jats:italic>
species, have abundant
<jats:italic>c-</jats:italic>
type cytochromes. Analysis of the recently completed genome sequence of
<jats:italic>Pelobacter carbinolicus</jats:italic>
revealed 14 open reading frames that could encode
<jats:italic>c</jats:italic>
-type cytochromes. Transcripts for all but one of these open reading frames were detected in acetoin-fermenting and/or Fe(III)-reducing cells. Three putative
<jats:italic>c</jats:italic>
-type cytochrome genes were expressed specifically during Fe(III) reduction, suggesting that the encoded proteins may participate in electron transfer to Fe(III). One of these proteins was a periplasmic triheme cytochrome with a high level of similarity to PpcA, which has a role in Fe(III) reduction in
<jats:italic>Geobacter sulfurreducens</jats:italic>
. Genes for heme biosynthesis and system II cytochrome
<jats:italic>c</jats:italic>
biogenesis were identified in the genome and shown to be expressed. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels of protein extracted from acetoin-fermenting
<jats:italic>P. carbinolicus</jats:italic>
cells contained three heme-staining bands which were confirmed by mass spectrometry to be among the 14 predicted
<jats:italic>c</jats:italic>
-type cytochromes. The number of cytochrome genes, the predicted amount of heme
<jats:italic>c</jats:italic>
per protein, and the ratio of heme-stained protein to total protein were much smaller in
<jats:italic>P. carbinolicus</jats:italic>
than in
<jats:italic>G. sulfurreducens</jats:italic>
. Furthermore, many of the
<jats:italic>c</jats:italic>
-type cytochromes that genetic studies have indicated are required for optimal Fe(III) reduction in
<jats:italic>G. sulfurreducens</jats:italic>
were not present in the
<jats:italic>P. carbinolicus</jats:italic>
genome. These results suggest that further evaluation of the functions of
<jats:italic>c</jats:italic>
-type cytochromes in the
<jats:italic>Geobacteraceae</jats:italic>
is warranted.
</jats:p>