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Linear osmoregulated periplasmic glucans are encoded by the opgGH locus of Pseudomonas aeruginosa

Yannick Lequette^1,

¹ Department of Microbiology, University of Washington, Seattle, WA 98195, USA
² Unité de Glycobiologie Structurale et Fonctionnelle CNRS UMR 8576, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq Cedex, France

Correspondence
Yannick Lequette
yannick.lequette{at}lille.inra.fr

Osmoregulated periplasmic glucans (OPGs) are produced by many proteobacteria and are important for bacterial–host interactions. The opgG and opgH genes involved in the synthesis of OPGs are the most widely distributed genes in proteobacterial genomes. Two other non-homologous genes, both named ndvB, are also involved in OPG biosynthesis in several species. The Pseudomonas aeruginosa genome possesses two ORFs, PA5077 and PA5078, that show similarity to opgH and opgG of Pseudomonas 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 β-1,2-linked glucosyl residues branched with a few β-1,6 glucosyl residues. Succinyl residues also substitute this glucose backbone. Transcription of opgGH is repressed by high osmolarity. Low osmolarity promotes the formation of highly structured biofilms, but biofilm development is slower and the area of biomass is reduced under high osmolarity. Biofilm development of an opgGH mutant grown under low osmolarity presents a similar phenotype to the wild-type biofilm grown under high osmolarity. These results suggest that OPGs are important for biofilm formation under conditions of low osmolarity. A previous study suggested that the P. aeruginosa ndvB gene is involved in the resistance of biofilms to antibiotics. We have shown that ndvB is not involved in the biosynthesis of the OPG described here, and opgGH do not appear to be involved in the resistance of P. aeruginosa PA14 biofilms to antibiotics.

Present address: LGPTA, CERTIA, INRA, 369 rue Guelde, 59651 Villeneuve d'Ascq, France.

Supplementary figures showing growth curves of PA14 parent and YL119 strains, and biofilm formation in the YL119 mutant complemented with pYL205-G are available with the online version of this paper.