Comparative proteomic analysis revealing ActJ-regulated proteins in Sinorhizobium meliloti

ABSTRACT: Acidic soil disturbs the establishment of the efficient rhizobia commonly used as biofertilizer and the plant-rhizobia interactions. To adapt to different environmental conditions, Sinorhizobium meliloti relies on a complex and finely tuned regulatory network. Although parts of this network have been well-elucidated, most S. meliloti transcriptional regulators remain unexplored. We recently reported that deletion of the ActJK two-component system renders an acid-vulnerable phenotype in S. meliloti and demonstrated the system's requirement for full bacteroid development and nodule occupancy. To more fully understand the role of ActJ in acid tolerance, the proteomes of wild type S. meliloti 2011 and the isogenic actJ- mutant strain were compared in the presence or absence of acid stress by nanoflow ultrahigh-performance liquid chromatography coupled to mass spectrometry. That analysis demonstrated that proteins related to cell wall, membrane, and envelope biogenesis such as those involved in the synthesis of exopolysaccharides (EPS) were notably enriched in actJ- cells in acid pH. Total EPS quantification supported these findings; revealing that although EPS production was augmented at pH 5.6 in both the actJ- and the parental strain, the lack of ActJ significantly enhanced this difference. Moreover, several efflux pumps were found downregulated in the actJ- strain. Promoter fusion assays suggested that ActJ positively modulated its own expression in acid medium but not at neutrality. Irrespective of the extracellular pH, NtrB -a sensory histidine kinase/phosphatase- and DegP1 -a key serine protease mediating protein quality control in diverse Gram-negative bacteria-, are both differentially expressed when ActJ is absent. Unraveling of ActJK-regulated mechanisms will help to understand how this organism deals with the acid stress naturally encountered in soils, infection threads, and symbiosomes. Results presented here identified several ActJ-regulated genes, highlighting key components of the regulatory network associated with the ActJK two-component system in S. meliloti and that system's role in the response of rhizobia to acid stress.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Sinorhizobium Meliloti (ncbitaxon:382)

SUBMITTER: Maria Florencia Del Papa  

PROVIDER: MSV000090690 | MassIVE | Thu Nov 10 11:57:00 GMT 2022

SECONDARY ACCESSION(S): PXD038087

REPOSITORIES: MassIVE