Alteration of lipopolysaccharide and protein profiles in SDS-PAGE of rhizobia by osmotic and heat stress

Abstract

The effects of osmotic and heat stress on lipopolysaccharides and proteins of rhizobia isolated from the root nodules of leguminous trees grown in semi-arid soils of the Sudan, and of agricultural legumes grown in salt-affected soils of Egypt, were determined by SDS-PAGE. The rhizobia were of three types: (1) sensitive strains, unable to grow in 3% (w/v) NaCl in yeast mannitol medium; (2) tolerant strains which could grow in 3% (w/v) NaCl; and (3) halophytic strains which grew with 3 to 10% (w/v) NaCl. The sensitive strains changed their gel pattern or the amount of lipopolysaccharide they synthesized when grown in 1% (w/v) NaCl. The tolerant and halophytic strains often modified their lipopolysaccharides in 3% NaCl, which was evident by a shift in the banding patterns towards longer chain length. Similar effects were observed in cells incubated with sucrose and, to a lesser extent, in cells incubated at growth temperatures near the recorded maximum temperature for growth. The stress-induced changes in lipopolysaccharides were not associated with specific banding patterns of the lipopolysaccharides. During incubation in medium containing elevated concentrations of NaCl or sucrose, the protein patterns of the rhizobia were also changed. A protein with relative mobility of 65 kDa appeared during temperature stress. The maximum growth temperature of the Sudanese rhizobia were up to 44.2°C.