The Mineral Nutrition of Rhizopus stolonifer

Summary: A series of experiments with culture media was carried out dealing with: (1) the action of different salts and their interaction in the medium; (2) the relation of the nitrogen source to the action of the salts; (8) the effect of the carbon source; (4) the proportionate influence of the salts in the medium; (5) the rate of growth. The results showed that this fungus grew well at 26° with an initial pH value of 7·0–8·0 and a growth period of 6–7 days. Statistical analysis of the results showed: (a) that under the given conditions an aqueous medium containing: 4%(w/v) glucose; 0–048 m-K2HPO4 ; 0·012 m-MgSO4.7H2O; 0·025 m-(NH4)2SO4; 2p.p.m. Zn, Fe and Mn, produced optimal growth measured as mg. dry wt.; (b) a balance did not exist between KCl, K2HPO4 and MgSO4; (c) a balance did not exist between the concentration of glucose and (NH4)2SO4; (d) a balance existed between K2HPO4 and (NH4)2SO4; (e) this fungus could only utilize KNO3 or Ca(NO3)2 to a negligible extent, while the best source found for nitrogen was (NH4)2SO4; the most available phosphorus source was K2HPO4; (f) the rate of growth followed a sigmoid curve in a nutritionally optimal solution but in the minimal solution used the onset of decline in dry weight was delayed; (g) the importance of a balanced solution is that in suitable media the buffering action of the phosphate controls the onset of acidity inimical to growth.