Nucleotide sequence of a regulatory region controlling alginate synthesis in Pseudomonas aeruginosa: characterization of the algR2 gene.

Alginate (Alg), an exopolysaccharide with strong gelling properties, is produced by Pseudomonas aeruginosa primarily during its infection of the cystic fibrosis (CF) lung. The alg genes are normally not expressed in other environments. The promoter for a critical Alg biosynthetic gene, algD, encoding GDP-mannose dehydrogenase, is activated only under conditions reminiscent of the CF lung (i.e., under high osmolarity), and at least two regulatory genes, algR1 and algR2, have been implicated in this activation process. The physical mapping of a 4.4-kb region harboring algR2 has been accomplished and the complete nucleotide sequence of this fragment, including that of algR2, is presented. The cloning and complementation experiments also demonstrate the presence, on this fragment, of regulatory gene(s) different from algR1 and algR2. The expression of the algR2 gene allows a high level of activation of the algD promoter in Escherichia coli, in the presence of algR1 in a high osmotic environment, suggesting that the AlgR2 and AlgR1 proteins act cooperatively to activate the algD promoter. Hyperexpression of the algR2 gene from the tac promoter also allows the conversion of nonmucoid cells of strain 8822, a spontaneous revertant of the mucoid CF isolate strain 8821, back to mucoidy, but not that of the clinical isolate, strain PAO1.