EFFECTS OF SODIUM-CHLORIDE AND MELIBIOSE ON THE INVITRO GROWTH AND SPORULATION OF FRANKIA STRAIN HFPCCI3 ISOLATED FROM CASUARINA-CUNNINGHAMIANA

The in vitro growth and sporulation of Frankia isolate HFPCcI3, a nitrogen-fixing symbiont of Casuarina, was inhibited by both the toxic and osmotic effects of sodium chloride. This was demonstrated by comparing HFPCcI3 halotolerance with its tolerance to metabolically neutral melibiose osmoticum at sodium chloride and melibiose concentrations from 0 to 500 mmol L-1. The osmotolerance of this strain is similar to that of other Frankia strains, whereas the halotolerance of this strain is greater than that reported for Frankia strains isolated from actinorhizal plants from moist, temperate regions lacking sodic soils. This finding suggests that differential strain-specific mechanisms are involved in Frankia's ability to tolerate dry versus sodic soil conditions and has important implications for the microbial ecology of soils supporting Casuarina spp.