Genetic Aspects of Mechanosensitivity in the Alphaproteobacteria Azospirillum baldaniorum with Mixed Flagellation

The aim of this work was to test the hypothesis that a putative multisensory hybrid histidine kinase-response regulator (HSHK-RR) and FlhB (a component of the type 3 secretion apparatus located in the basal body of Fla) encoded by Azospirillum baldaniorum Sp245 by adjacent chromosomal genes, are involved in mechanosensing and mechanotransduction. We used Sp245 strains and its Fla(-)Laf(-) mutant Sp245.1063 (flhB1::Omegon-Km). To construct A. baldaniorum derivatives with an increased dose of CDS AZOBR_150176 (HSHK-RR), this sequence of strain Sp245 was cloned in the pRK415 expression vector. The resulting structure was transferred to Sp245 and Sp245.1063 bacteria. Cell morphology was studied using phase-contrast and transmission electron microscopy. The relative amount of biofilm biomass was determined by staining the bacteria with a crystal violet. Derivatives of the Sp245 strain and its immotile mutant Sp245.1063 (flhB1::Omegon-Km) with an increased dose of HSHK-RR were obtained. It was found that a mutation in the gene encoding the FlhB protein or an increase in the copy number of the gene encoding HSHK-RR affect the motility and ultrastructure of cells, the dynamics of changes in cell size and the flagellation when changing the mechanical properties of the medium. Primary data have been obtained indicating that the cell membrane-associated FlhB proteins and HSHK-RR are involved in the perception of changes in the mechanical properties of the medium and in the transmission of the corresponding mechanical signals in A. baldaniorum cells.

Automated summary

The aim of this study was to investigate the involvement of the HSHK-RR and FlhB proteins in mechanosensing and mechanotransduction in Azospirillum baldaniorum cells. The results demonstrated that mutations in the FlhB gene or an increase in the copy number of the HSHK-RR gene affected cell motility, ultrastructure, and dynamics of cell size changes. It was also found that these proteins are involved in the perception and transmission of mechanical signals in response to changes in the mechanical properties of the medium.