THE METABOLISM OF GIBBERELLA FUJIKUROI IN STIRRED CULTURE

Abstract

The growth of Gibberella fujikuroi in stirred culture was studied. Media were designed in which the initial concentrations of glucose (G), nitrogen (N), phosphorus (P), and magnesium (M) were varied so that the first nutrient was exhausted at a selected dry weight, and the remaining nutrients in all available sequences thereafter. Distinct phases of growth, related to the changing nutritional status of the mold, have been defined.The balanced phase was a period of proliferation in the presence of all nutrients, during which a unit increase in dry mycelium was accompanied by constant uptakes of G, N, P, M, and potassium (K). The morphology remained virtually unchanged, and the dry mycelium contained ca. 6% fat, ca. 16% carbohydrate, and ca. 13% phosphorus-containing compounds, and the fractions of each remained constant. This phase continued until the first nutrient was exhausted. Proliferation, indicated by increases in fat- and carbohydrate-free dry weight, then ceased in N- and G-limited fermentations. In P- and M-limited fermentations, proliferation continued until the subsequent exhaustion of either G or N, and during this transition phase the carbohydrate content of the mycelium increased, while in M-limited fermentations the fat content also increased. In P-limited fermentations the uptake of both M and K ceased, and reserves of metaphosphate were used.At the exhaustion of N in N-, P-, or M-limited fermentations, proliferation ceased but the dry weight continued to increase due to increases in carbohydrate and triglyceride. In the presence of sufficient glucose, maximum amounts of 45% fat, visible as oil globules, and 32% carbohydrate were formed, but in the presence of less G these ceased to increase when G was exhausted before these maxima were reached. In either case the maintenance phase followed, during which all mycelial components remained constant except the triglycerides, which decreased when exhaustion of G had initiated the maintenance phase; otherwise they also remained constant until G was subsequently exhausted, and then decreased. The terminal phase began when the triglycerides were exhausted, and also when G was exhausted in G-limited fermentations, or in P- and M-limited fermentations in which G was exhausted before N. This phase was characterized by hyphal breakdown, a decrease in dry weight, and the liberation of mycelial components into the medium.