A role for exopolysaccharides in the protection of microorganisms from desiccation.

Mucoid strains of Escherichia coli, Acinetobacter calcoaceticus, and Erwinia stewartii were significantly more resistant to desiccation than corresponding isogenic nonmucoid mutants (survival rates of up to 35% in mucoid strains and between 0.7 and 5% in nonmucoid variants), even in colonies containing both cell types. Desiccation was found to bring about an induction of beta-galactosidase in Lon strains of E. coli K-12 carrying transcriptional lac fusions in the capsule biosynthetic (cps) regulon. This induction was dependent on the transcriptional activators RcsA and RcsB. Induction was lower in cells carrying mutations in the membrane sensor protein RcsC.