| Abstrakt: |
The effect was analyzed of the flhB2 gene, which is located on the AZOBR_p4 (AZOBR_p410073 gene) plasmid in Azospirillum baldaniorum Sp245 and on the ABSP7_p3 (AMK58_26270 gene) plasmid in A. brasilense Sp7 and codes for the FlhB protein, a flagellar export component that ensures flagellin assembly, flagellation, and motility in these bacteria. We used A. baldaniorum strain Sp245, its Fla– Laf– mutant Sp245.1063 (Sp245-flhB1::Omegon-Km), and A. brasilense Sp7. Mutants defective in the flhB2 gene were generated by site-directed mutagenesis. Bacterial morphology and motility were characterized by electron and phase-contrast microscopy. An A. baldaniorum Sp245 mutant, Sp245-flhB2::Km, was generated that had a cloned kanamycin resistance gene in the coding sequence (CDS) AZOBR_p410073. In contrast to the Fla– Laf– mutant Sp245-flhB1::Omegon-Km, the flhB1 chromosomal gene of which is inactivated (AZOBR_150177 gene), strain Sp245-flhB2::Km retained the synthesis of a functioning polar flagellum (Fla), but the synthesis and functioning of lateral flagella (Laf) was impaired and the movement and spreading rates of swarming cells in semiliquid agarized media were decreased. Inactivation of the AMK58_26270 plasmid gene in Sp7, which is homologous to the AZOBR_p410073 gene (97% identity), resulted in a similar Laf– phenotype in the corresponding mutant. Two putative flhB genes are present in the genome of strains Sp245 and Sp7. These genes are located in the chromosome (flhB1) and on the AZOBR_p4 or ABSP7_p3 plasmid (flhB2), respectively. Expression of the flhB2 gene is required for Laf assembly. Transcription of flhB2 is regulated by a mechanosignal, the perception and generation of which is ensured by the functioning Fla, apparently with the involvement of the FlhB protein encoded by the flhB1 chromosomal gene. [ABSTRACT FROM AUTHOR] |
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