A role for osmotic stress-induced proteins in the osmotolerance of a nitrogen-fixing cyanobacterium, Anabaena sp. strain L-31.

The molecular basis of tolerance to osmotic stress was investigated with a cyanobacterium, Anabaena sp. strain L-31. The inherent osmotolerance of this strain (50% growth inhibition at 350 mM sucrose) was enhanced by adaptation with 100 mM sucrose for 30 min. Addition of 10 mM KNO3 during growth also conferred significant osmoprotection, but addition of 3 mM NH4Cl did not. Exposure of cells to 350 mM sucrose induced the expression of at least 12 osmotic-stress-induced proteins (OSPs) within 30 min, in the molecular mass range of 11.5 to 84 kDa. Exposure of cells to 100 mM sucrose or to 10 mM nitrate also induced all the OSPs, but addition of ammonium did not. The observed correspondence between the presence of OSPs and osmotolerance strongly suggests a role for OSPs in osmotolerance of Anabaena sp. strain L-31.