N-Acetylglucosamine-dependent biofilm formation in Pectobacterium atrosepticum is cryptic and activated by elevated c-di-GMP levels

Abstract

The phytopathogenic bacteriumPectobacterium atrosepticum(Pba) strain SCRI1043 does not exhibit appreciable biofilm formation under standard laboratory conditions. Here we show that a biofilm-forming phenotype in this strain could be activated from a cryptic state by increasing intracellular levels of c-di-GMP, through overexpression of a constitutively active diguanylate cyclase (PleD*) fromCaulobacter crescentus. Randomly obtainedPbatransposon mutants defective in thepgaoperon, involved in synthesis and translocation of poly-β-1,6-N-acetyl-d-glucosamine (PGA), were all impaired in this biofilm formation. The presence of the PGA-degrading enzyme dispersin B in the growth media prevented biofilm formation byPbaoverexpressing PleD*, further supporting the importance of PGA for biofilm formation byPba. Importantly, apgamutant exhibited a reduction in root binding to the host plant under conditions of high intracellular c-di-GMP levels. A modest but consistent increase inpgatranscript levels was associated with high intracellular levels of c-di-GMP. Our results indicate tight control of PGA-dependent biofilm formation by c-di-GMP inPba.