Affiliation:
1. Lehrstuhl für Technische Mikrobiologie, Fachbereich Chemietechnik, Universität Dortmund, D-44221 Dortmund, Germany
Abstract
ABSTRACT
A transposon Tn
5-mob
insertional mutant of
Paracoccus pantotrophus
GB17, strain TP43, was unable to oxidize thiosulfate aerobically or to reduce nitrite anaerobically, and the cellular yields were generally decreased by 11 to 20%. Strain TP43 was unable to form functional
c-
type cytochromes, as determined by difference spectroscopy and heme staining. However, formation of apocytochromes and their transport to the periplasm were not affected, as seen with SoxD, a
c
-type cytochrome associated with the periplasmic sulfite dehydrogenase homologue. The Tn
5-mob
-containing DNA region of strain TP43 was cloned into pSUP205 to produce pE18TP43. With the aid of pE18TP43 the corresponding wild-type gene region of 15 kb was isolated from a heterogenote recombinant to produce pEF15. Sequence analysis of 2.8 kb of the relevant region uncovered three open reading frames, designated ORFA,
ccdA
, and ORFB, with the latter being oriented divergently. ORFA and
ccdA
were constitutively cotranscribed as determined by primer extension analysis. In strain TP43 Tn
5-mob
was inserted into
ccdA
. The deduced ORFA product showed no similarity to any protein in databases. However, the
ccdA
gene product exhibited similarities to proteins assigned to different functions in bacteria, such as cytochrome
c
biogenesis. For these proteins at least six transmembrane helices are predicted with the potential to form a channel with two conserved cysteines. This structural identity suggests that these proteins transfer reducing equivalents from the cytoplasm to the periplasm and that the cysteines bring about this transfer to enable the various specific functions via specific redox mediators such as thioredoxins. CcdA of
P. pantotrophus
is 42% identical to a protein predicted by ORF2, and its location within the
sox
gene cluster coding for lithotrophic sulfur oxidation suggested a different function.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
29 articles.
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