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Multiple phenotypic alterations caused by a c-type cytochrome maturation ccmC gene mutation in Pseudomonas aeruginosa

¹ VIB, Department of Molecular and Cellular Interactions, Laboratory of Microbial Interactions, Vrije Universiteit Brussel, Building E, room 6.6, Pleinlaan 2, B-1050 Brussels, Belgium
² UMR6026, Interactions Cellulaires et Moléculaires, Université de Rennes 1, Campus de Beaulieu, avenue du Général Leclerc, 35042 Rennes cedex, France

Correspondence
Pierre Cornelis
pcornel{at}vub.ac.be

In some Proteobacteria biogenesis of c-type cytochromes depends on the products of the ccmABCDEFG(H) genes, which encode inner-membrane proteins. Inactivation of some ccm genes, in particular ccmC, has an impact on other processes as well, including siderophore production and utilization. Non-polar insertions were generated in the Pseudomonas aeruginosa ccmA, ccmC, ccmE, ccmF and ccmH genes, and their impacts on different phenotypes were compared. Only in the case of the ccmC mutant was cytochrome c production totally abrogated. The ccmC mutant, and to a lesser extent the ccmF mutant, showed a range of other phenotypic changes. The production of the siderophore pyoverdine was very low and growth under the condition of iron limitation was severely restricted, but production of the second siderophore, pyochelin, was increased. Interestingly, other traits were also strongly affected by the ccmC mutation, including the production of pyocyanin, swarming and twitching motility, and rhamnolipid production. The production of N-acyl homoserine lactones or the Pseudomonas quinolone signal (PQS) was, however, not affected in the ccmC and ccmF mutants. The ccmC mutant was also found to accumulate porphyrins, and catalase production was undetectable, consistent with the increased sensitivity to hydrogen peroxide. Finally, reduction in the content of [Fe–S] clusters was evidenced in both ccmC and ccmF mutants. Wild-type phenotypes were restored by complementation with a ccmC gene from Pseudomonas fluorescens ATCC 17400. In conclusion, we have demonstrated that CcmC is a key determinant for cytochrome c biogenesis, pyoverdine maturation, and expression of some quorum sensing-regulated traits.

A supplementary figure showing production of quorum-sensing signal molecules and two video clips showing motility of wild-type and ccmC mutant P. aeruginosa are available with the online version of this paper.