Regulation of Macromolecular Synthesis, Colony Development, and Specific Growth Rate of Achlya bisexualis during Balanced Growth

Summary: The growth of Achlya bisexualis Coker & Couch on four different nitrogen sources was studied. Growth in submerged culture was filamentous and followed exponential growth kinetics. The organism’s specific growth rate varied with the nitrogen source and method of agitation. RNA content of the mycelium increased linearly with the organism’s specific growth rate, but its DNA and protein contents remained constant. Differences in specific growth rate caused by the N sources were directly related to colony radial-growth rate, branching rate, and width of the peripheral growth zone. The distance from the hyphal tip to the first branch decreased to a minimum value with increased specific growth rate. Mycelial RNA content was generally correlated with specific growth rate. The doubling time of 51 min observed on casein hydrolysate at 24 °C is believed to be the fastest recorded for any eucaryote.