SUBMERGED BATCH CULTURE OF THE PSYCHROPHILE MONOGRAPHELLA-NIVALIS IN A DEFINED MEDIUM - GROWTH, CARBOHYDRATE UTILIZATION AND RESPONSES TO TEMPERATURE

An asporogenous strain of the pink snow mould fungus, Monographella ni valis (Schaffnit) E. Muller, anamorph Gerlachia nivalis (Ces. ex Sac.) W. Gams and E. Muller (Syn. Fusarium nivale Ces. ex Sacc.), grew at 5 degrees C on a defined salts medium plus vitamins and utilized a vari ety of simple and polymeric carbohydrates as the sole carbon and energ y source. Mycelium was grown at temperatures between 3 and 15 degrees C in aerated submerged fermentation culture in chemically defined medi um plus sucrose. Optimum growth rates of 0.035-0.033 h(-1) occurred be tween 9 and 12 degrees C. Growth in a simple medium showed that all bi ochemical and physiological processes necessary for growth were functi onal at 3 degrees C. The growth performance of the organism at low tem peratures was no better than would be expected from extrapolation of m esophilic growth responses to temperature. The optimum growth temperat ure of 9-12 degrees C showed that some biochemical or physiological pr ocess was impaired above 12 degrees C. Uptake and incorporation of S-3 5-methionine by mycelium at different temperatures showed that general protein synthesis increased up to 25 degrees C, and hence was not res ponsible per se for the sensitivity-to temperatures above 12 degrees C . Heat shock proteins were synthesized at the relatively low temperatu re of 25 degrees C, consistent with the low temperature optimum for gr owth. When grown with sucrose as the sole carbon source, the mycelium catalyzed the extracellular hydrolysis of sucrose, releasing glucose a nd fructose together with a small amount of fructan trisaccharides and a trace of tetra- and penta-saccharides. Fructan accumulation was tra nsient, corresponding with maximal rates of sucrose hydrolysis. Most b iomass formation occurred in the absence of fructan in the culture, he nce fructan was not necessary for growth at low temperature and did no t appear to function as a cryoprotectant. Invertase activity was mostl y (60-70%) bound to mycelium; the remainder was free in the culture su pernatant. The regulation of invertase expression appeared to be by su crose-induction, rather than by end-product repression. Rates of sucro se hydrolysis in culture were temperature-sensitive and were markedly depressed above 12 degrees C, indicating inhibition of invertase forma tion.