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Open Access Research article

Identification of a predicted partner-switching system that affects production of the gene transfer agent RcGTA and stationary phase viability in Rhodobacter capsulatus

Ryan G Mercer12 and Andrew S Lang1*

Author Affiliations

1 Department of Biology, Memorial University of Newfoundland, 232 Elizabeth Ave, St. John’s A1B 3X9, NL, Canada

2 Current address: Department of Agricultural, Food and Nutritional Science, University of Alberta, 2-46 Agriculture Forestry Centre, Edmonton T6G 2P5, AB, Canada

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BMC Microbiology 2014, 14:71  doi:10.1186/1471-2180-14-71

Published: 19 March 2014



Production of the gene transfer agent RcGTA in the α-proteobacterium Rhodobacter capsulatus is dependent upon the response regulator protein CtrA. Loss of this regulator has widespread effects on transcription in R. capsulatus, including the dysregulation of numerous genes encoding other predicted regulators. This includes a set of putative components of a partner-switching signaling pathway with sequence homology to the σ-regulating proteins RsbV, RsbW, and RsbY that have been extensively characterized for their role in stress responses in gram-positive bacteria. These R. capsulatus homologues, RbaV, RbaW, and RbaY, have been investigated for their possible role in controlling RcGTA gene expression.


A mutant strain lacking rbaW showed a significant increase in RcGTA gene expression and production. Mutation of rbaV or rbaY led to a decrease in RcGTA gene expression and production, and these mutants also showed decreased viability in the stationary phase and produced unusual colony morphologies. In vitro and in vivo protein interaction assays demonstrated that RbaW and RbaV interact. A combination of gene disruptions and protein-protein interaction assays were unsuccessful in attempts to identify a cognate σ factor, and the genetic data support a model where the RbaV protein that is the determinant regulator of RcGTA gene expression in this system.


These findings provide new information about RcGTA regulation by a putative partner-switching system and further illustrate the integration of RcGTA production into R. capsulatus physiology.

Gene expression; Protein-protein interactions; Partner-switching; Gene exchange