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Journal of Bacteriology, June 2005, p. 4245-4256, Vol. 187, No. 12
0021-9193/05/$08.00+0     doi:10.1128/JB.187.12.4245-4256.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Overproduction of CcmG and CcmFH_Rc Fully Suppresses the c-Type Cytochrome Biogenesis Defect of Rhodobacter capsulatus CcmI-Null Mutants

Carsten Sanders,¹ Meenal Deshmukh,^1, Doniel Astor,¹ Robert G. Kranz,² and Fevzi Daldal^1*

Department of Biology, Plant Science Institute, University of Pennsylvania, Philadelphia, Pennsylvania 19104,¹ Department of Biology, Washington University, St. Louis, Missouri 63130²

Received 12 January 2005/ Accepted 11 March 2005

Gram-negative bacteria like Rhodobacter capsulatus use intertwined pathways to carry out the posttranslational maturation of c-type cytochromes (Cyts). This periplasmic process requires at least 10 essential components for apo-Cyt c chaperoning, thio-oxidoreduction, and the delivery of heme and its covalent ligation. One of these components, CcmI (also called CycH), is thought to act as an apo-Cyt c chaperone. In R. capsulatus, CcmI-null mutants are unable to produce c-type Cyts and thus sustain photosynthetic (Ps) growth. Previously, we have shown that overproduction of the putative heme ligation components CcmF and CcmH_Rc (also called Ccl1 and Ccl2) can partially bypass the function of CcmI on minimal, but not on enriched, media. Here, we demonstrate that either additional overproduction of CcmG (also called HelX) or hyperproduction of CcmF-CcmH_Rc is needed to completely overcome the role of CcmI during the biogenesis of c-type Cyts on both minimal and enriched media. These findings indicate that, in the absence of CcmI, interactions between the heme ligation and thioreduction pathways become restricted for sufficient Cyt c production. We therefore suggest that CcmI, along with its apo-Cyt chaperoning function, is also critical for the efficacy of holo-Cyt c formation, possibly via its close interactions with other components performing the final heme ligation steps during Cyt c biogenesis.

Present address: Colgate-Palmolive Inc. Research Center, Piscataway, N.J.

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