OBJECTIVE
The aim of the work is to test the hypothesis about the effect of the chromosome-located HSHK-RR gene encoding a hybrid multisensory histidine kinase on the morphology of bacteria of the genus Azospirillum.
MATERIAL AND METHODS
The strains A. baldaniorum Sp245, Lafˉ mutant Sp245.1062 (Sp245-HSHKDRR-Km), A. brasilense Sp7 and Sp7.10030 (Sp7-HSHKDRR-Km) were used in the work. Bacterial morphology and motility were characterized by electron microscopy. The relative level of gene transcription was determined by real-time PCR.
RESULTS
The hybrid multisensory histidine kinase (HSHK-RR) genes in Sp245 (AZOBR_150176) and Sp7 (AMK58_10030) strains are 95% homologous. Replacement of the internal fragment of the HSHK-RR gene with the kanamycin resistance gene resulted resulted in changes in the morphology and motility of cells in semi-liquid agar in the Sp245-HSHKDRR-Km and Sp7-HSHKDRR-Km mutants. The mutant cells were shorter than the cells of the strains Sp245 and Sp7 and moved more slowly in semi-liquid agar, forming colonies of a significantly smaller diameter.
Both mutants retained the synthesis of a functioning polar flagellum (Fla). However, in the case of Sp7-HSHKDRR-Km, up to 45% of the cells synthesized rare or single lateral flagella (Laf) on agar media, whereas in Sp245-HSHKDRR-Km, no more than 15% of such cells were present.
CONCLUSION
It was established that Laf biogenesis is under multistage control, including a two-component signal transduction system involving HSHK-RR encoded by chromosomal genes in Sp245 and Sp7, respectively, strains AZOBR_150176 and AMK58_10030. Phenotype analysis of mutants for the AZOBR_150176 and AMK58_10030 genes showed that the studied HSHK-RR modulates the motility of Sp245 and Sp7 under mechanical stress, participating in the transcription control of the flagellin laf1 genes and components of the export system of lateral flagella assembly.