The GacS sensor kinase regulates alginate and poly-beta-hydroxybutyrate production in Azotobacter vinelandii

Azotobacter vinelandii produces two polymers: the extracellular polysacchar ide alginate and the intracellular polyester poly-beta-hydroxybutyrate (PHB ), A cosmid clone (pSMU588) from an A. vinelandii gene library diminished a lginate production A.. vinelandii mucoid strain ATCC 9046. The nucleotide s equence and predicted amino acid sequence of the locus responsible for the mucoidy suppression revealed 65% identity to Pseudomonas GacS, a transmembr ane sensor kinase of the two-component regulators, whose cognate response r egulator, GacA, is a global activator regulating several products and virul ence factors. Plasmid pMC15, harboring gacS, and a strain carrying a gacS n onpolar mutation were constructed. Either pMC15 or the gacS mutation signif icantly reduced alginate production and transcription of algD, the gene cod ing for the key enzyme GDP-mannose dehydrogenase of the alginate biosynthet ic pathway. We found that the gacS mutation also reduced PHB accumulation a nd impaired encystment. Taken together, these data indicate that in A. vine landii the gacSA global system regulates polymer synthesis.