Evidence for a functional similarity between the two-component regulatory systems RegSR, ActSR, and RegBA (PrrBA) in α-proteobacteria

• Published in: Archives of microbiology 2000-11, Vol.174 (5), p.307-313
• Main Authors: EMMERICH, Ralf, HENNECKE, Hauke, FISCHER, Hans-Martin
• Format: Article
• Language: English
• Subjects: acid tolerance; ActSR protein; Alphaproteobacteria - genetics; Alphaproteobacteria - physiology; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacteriology; Biological and medical sciences; Bradyrhizobium japonicum; Carbon Dioxide - metabolism; Escherichia coli; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Bacterial - genetics; Genetics; Hydrogen-Ion Concentration; Microbiology; Nitrogen Fixation - genetics; Nitrogen Fixation - physiology; Permeability, membrane transport, intracellular transport; Photosynthetic Reaction Center Complex Proteins - genetics; Photosynthetic Reaction Center Complex Proteins - metabolism; Proteobacteria; PrrBA protein; RegBA protein; RegSR protein; Rhodobacter capsulatus; Signal Transduction - genetics; Sinorhizobium meliloti; Symbiosis; Transcription Factors - genetics; Transcription Factors - metabolism
• ISSN: 0302-8933; 1432-072X
• DOI: 10.1007/s002030000207

The symbiotic bacteria Bradyrhizobium japonicum and Sinorhizobium meliloti, and the purple photosynthetic bacteria Rhodobacter capsulatus, Rhodovulum sulfidophilum, Roseobacter denitrificans and Rhodobacter sphaeroides possess homologous two-component regulatory systems, namely RegSR, ActSR, RegBA and PrrBA. The respective response regulators of these bacteria control expression of different regulons that are involved in N2 fixation, CO2 fixation, photosynthesis or acid tolerance. We therefore asked whether the regulators are functionally exchangeable or whether they have disparate functions in the different species, despite the amino acid sequence similarity. In this study, we showed that purified B. japonicum RegR bound in vitro to genuine DNA targets for Rba. capsulatus RegA, and that RegA was phosphorylated in vitro when RegSc (a soluble variant of the sensor kinase RegS) was added to an Escherichia coli extract containing overexpressed RegA. In vivo, RegA and S. meliloti ActR activated transcription of the B. japonicum fixR-nifA operon, normally a target for RegR. The genes for both regulators, regA and actR, were able to complement a B. japonicum regR mutant with respect to the formation of a nitrogen-fixing symbiosis with soybean. Vice versa, RegR activated in Rba. capsulatus the expression of the photosynthesis operon puc, normally a target for RegA. In conclusion, the results show that B. japonicum RegR, Rba. capsulatus RegA, and S. meliloti ActR are functionally similar.