Control of alginate synthesis in Pseudomonas aeruginosa: regulation of the algR1 gene.

The triggering of mucoidy (formation of the exopolysaccharide alginate) in Pseudomonas aeruginosa is accomplished primarily in Cystic Fibrosis lung environment through activation of the promoter of a gene algD, which encodes GDP-mannose dehydrogenase, by the product of a regulatory gene algR1. Both algD and algR1 promoter regions have significant homology, including the presence of sequences recognized by the RNA polymerase sigma 54. We demonstrate that the algR1 promoter is partly constitutive and its activation, similar to that of algD, is dependent on high osmolarity as well as the presence of its own gene product and is repressed by high concentrations of AlgR1. The RpoN sigma factor also plays a critical role in the transcription of both algD and algR1 genes.