Affiliation:
1. Division of Biology
2. Division of Geological and Planetary Sciences
3. Howard Hughes Medical Institute, California Institute of Technology, Pasadena, California 91125
Abstract
ABSTRACT
Anoxygenic photosynthesis based on Fe(II) is thought to be one of the most ancient forms of metabolism and is hypothesized to represent a transition step in the evolution of oxygenic photosynthesis. However, little is known about the molecular basis of this process because, until recently (Y. Jiao and D. K. Newman, J. Bacteriol. 189:1765-1773, 2007), most phototrophic Fe(II)-oxidizing bacteria have been genetically intractable. In this study, we circumvented this problem by taking a heterologous-complementation approach to identify a three-gene operon (the
foxEYZ
operon) from
Rhodobacter
sp. strain SW2 that confers enhanced light-dependent Fe(II) oxidation activity when expressed in its genetically tractable relative
Rhodobacter capsulatus
SB1003. The first gene in this operon,
foxE
, encodes a
c
-type cytochrome with no significant similarity to other known proteins. Expression of
foxE
alone confers significant light-dependent Fe(II) oxidation activity on SB1003, but maximal activity is achieved when
foxE
is expressed with the two downstream genes
foxY
and
foxZ
. In SW2, the
foxE
and
foxY
genes are cotranscribed in the presence of Fe(II) and/or hydrogen, with
foxZ
being transcribed only in the presence of Fe(II). Sequence analysis predicts that
foxY
encodes a protein containing the redox cofactor pyrroloquinoline quinone and that
foxZ
encodes a protein with a transport function. Future biochemical studies will permit the localization and function of the Fox proteins in SW2 to be determined.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
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