The Sinorhizobium meliloti NspS-MbaA system affects biofilm formation, exopolysaccharide production and motility in response to specific polyamines

• Published in: Microbiology (Society for General Microbiology) Vol. 169; no. 1
• Main Authors: Chávez-Jacobo, Víctor M, Becerra-Rivera, Víctor A, Guerrero, Gabriela, Dunn, Michael F
• Format: Journal Article
• Language: English
• Published: England Microbiology Society 01-01-2023
• Subjects: Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biofilms; Gene Expression Regulation, Bacterial; Microbial Physiology, Biochemistry and Metabolism; Polyamines - metabolism; Polysaccharides, Bacterial - metabolism; Sinorhizobium meliloti - genetics; Sinorhizobium meliloti - metabolism; NspS-MbaA; S. meliloti; biofilm; cyclic di-GMP; exopolysaccharides; motility; polyamine sensing
• ISSN: 1350-0872; 1465-2080
• DOI: 10.1099/mic.0.001293

We previously showed that specific polyamines (PAs) present in the extracellular environment markedly affect extracellular polysaccharide (EPS) production, biofilm formation and motility in
Rm8530. We hypothesized that extracellular PA signals were sensed and transduced by the NspS and MbaA proteins, respectively, which are homologs of the PA-sensing, c-di-GMP modulating NspS-MbaA proteins described in
. Here we show that the decrease in biofilm formation and EPS production in the quorum-sensing (QS)-deficient
wild-type strain 1021 in cultures containing putrescine or spermine did not occur in a 1021
mutant (1021 nspS). The transcriptional expression of
in strain 1021 was significantly increased in cultures containing either of these polyamines, but not by exogenous cadaverine, 1,3-diaminopropane (DAP), spermidine (Spd) or norspermidine (NSpd). Cell aggregation in liquid cultures did not differ markedly between strain 1021 and 1021 nspS in the presence or absence of PAs. The
QS-proficient Rm8530 wild-type and
mutant (Rm8530 nspS) produced similar levels of biofilm under control conditions and 3.2- and 2.2-fold more biofilm, respectively, in cultures with NSpd, but these changes did not correlate with EPS production. Cells of Rm8530 nspS aggregated from two- to several-fold more than the wild-type in cultures without PAs or in those containing Spm. NSpd, Spd and DAP differently affected swimming and swarming motility in strains 1021 and Rm8530 and their respective
mutants.
transcription in strain Rm8530 was greatly reduced by exogenous Spm. Bioinformatic analysis revealed similar secondary structures and functional domains in the MbaA proteins of
and
, while their NspS proteins differed in some residues implicated in polyamine recognition in the latter species. NspS-MbaA homologs occur in a small subset of soil and aquatic bacterial species that commonly interact with eukaryotes. We speculate that the
NspS-MbaA system modulates biofilm formation, EPS production and motility in response to environmental or host plant-produced PAs.