ASSOCIATIONS AMONG HALOTOLERANCE, OSMOTOLERANCE AND EXOPOLYSACCHARIDE PRODUCTION OF AUREOBASIDIUM MELANOGENUM STRAINS FROM HABITATS UNDER SALT STRESS

Abstract

Associations among halotolerance, osmotolerance and exopolysaccharide (EPS) production of 50 Aureobasidium melanogenum strains isolated from various habitats along the coasts of Thailand were compared. Using Fisher's Exact Test, significant associations were found between halotolerance vs osmotolerance (P = 0.004), halotolerance vs EPS production (P = 0.049) and osmotolerance vs EPS production (p<<0.001). Highly to moderately halotolerant strains were found to be moderately osmotolerant, but not vice versa. Tolerant strains against either salt or sugar produced moderate to low EPS yield. Strains intolerant to salt and/or sugar varied widely in EPS production. The effect of osmotic stress on the growth and EPS yield were investigated with three strains different in halotolerance, osmotolerance and EPS production by comparing their cultures in media with increasing sucrose concentrations. As sucrose concentration increased, a significant reduction in conversion efficiency was observed. Both moderately halotolerant (PBUAP13) and osmotolerant (PBUAP50) strains with moderate EPS production lost their conversion efficiency more drastically than the relatively stress intolerant, high EPS producing strain (PBUAP34). The reduction in EPS production at high osmotic stress was apparently not the result of growth inhibition for both moderately tolerant strains. Cellular accumulation of mannitol was detected in all strains tested.