Linear osmoregulated periplasmic glucans are encoded by the opgGH locus of Pseudomonas aeruginosa
Résumé
Osmoregulated periplasmic glucans (OPG) are produced by many Proteobacteria. The OPG are important for bacterial-host interactions. The opgG and H genes involved in synthesis of OPG are the most represented genes in Proteobacteria genomes. Two other non-homolog genes, both named ndvB are also involved in OPG biosynthesis in several species. The Pseudomonas aeruginosa genome possesses two ORF, PA5077 and PA5078 that show similarity to opgH and opgG genes of P. syringae, respectively and one ORF, PA1163 similar to ndvB of Sinorhizobium meliloti. Here, we report that the opgGH locus of P. aeruginosa PA14 is involved in the synthesis of linear polymers with beta-1,2-linked glucosyl residues branched with few beta-1,6 glucosyl residues. Succinyl residues also substitute this glucose backbone. Transcription of opgGH is repressed by high osmolarity. Low osmolarity condition promotes formation of highly structured biofilm while biofilm development is slower and area of biomass is reduced in high osmolarity condition. Biofilm development of an opgGH mutant grown in low osmolarity condition presents a similar phenotype of wild type biofilm grown in high osmolarity condition. These results suggest OPG are important for biofilm formation in low osmolarity condition. A previous study suggested that the P. aeruginosa ndvB gene is involved in resistance of biofilm to antibiotics. We showed ndvB is not involved in biosynthesis of the OPG described here and opgGH do not appear to be involved in resistance of P. aeruginosa PA14 biofilms to antibiotics.