FlcA regulation of metabolism and stress response in 'Azospirillum brasilense' Sp7

Abstract

In 'Azospirillum brasilense', a possible transcriptional regulator, FlcA, controls the differentiation of cells from vegetative to cyst forms. In this study, a suicide plasmid pSUP-flcAΔ was constructed, and by homologous recombination between the plasmid and the genomic DNA of 'Azospirillum brasilense' Sp7, the open reading frame of flcA was deleted in the genome of wild-type Sp7. In contrast to wild-type 'A. brasilense' Sp7, this flcA in-frame knock-out strain, named Sp7-flcAΔ, did not aggregate and remained in vegetative form under flocculation conditions. These FlcA deficient bacteria binded weakly Congo-red, lacked an extra-cellular polysaccharides coat on their cell surface and lacked poly-β-hydroxybutyrate granules within the cells under flocculation conditions. Compared to the wild-type Sp7, Sp7-flcAΔ weakly attached to wheat roots, and showed a significant reduction of survival rates under stress conditions, like UV radiation, heat and osmotic stress.