Comparative Proteomic Analysis Revealing ActJ-Regulated Proteins in Sinorhizobium meliloti .
Francisco Javier AlbicoroCarolina VaccaJuan Hilario CafieroWalter Omar DraghiMaría Carla MartiniMark GoulianAntonio LagaresMaría Florencia Del PapaPublished in: Journal of proteome research (2023)
To adapt to different environmental conditions, Sinorhizobium meliloti relies on finely tuned regulatory networks, most of which are unexplored to date. We recently demonstrated that deletion of the two-component system ActJK renders an acid-vulnerable phenotype in S. meliloti and negatively impacts bacteroid development and nodule occupancy as well. To fully understand the role of ActJ in acid tolerance, S. meliloti wild-type and S. meliloti Δ act J proteomes were compared in the presence or absence of acid stress by nanoflow ultrahigh-performance liquid chromatography coupled to mass spectrometry. The analysis demonstrated that proteins involved in the synthesis of exopolysaccharides (EPSs) were notably enriched in Δ act J cells in acid pH. Total EPS quantification further revealed that although EPS production was augmented at pH 5.6 in both the Δ act J and the parental strain, the lack of ActJ significantly enhanced this difference. Moreover, several efflux pumps were found to be downregulated in the Δ act J strain. Promoter fusion assays suggested that ActJ positively modulated its own expression in an acid medium but not at under neutral conditions. The results presented here identify several ActJ-regulated genes in S. meliloti , highlighting key components associated with ActJK regulation that will contribute to a better understanding of rhizobia adaptation to acid stress.