A theory of the mode of growth of fungi in the form of pellets in submerged culture

Abstract

Fungi in submerged culture often grow in the form of compact spherical masses of mycelium known as pellets. Under certain conditions, it is postulated that the pellets consist of an outer shell of growing hyphae and an inner mass of non-growing mycelium. The kinetics of growth according to this model are analysed. The thickness of the outer growing layer of the pellet is considered to be limited by nutrient diffusion rate. Calculations of diffusion rates of required nutrients indicate that the growth-limiting nutrient will almost inevitably be oxygen if air is supplied at one atmosphere even though the medium is saturated with oxygen. Thus the mycelium inside the outer growing shell of the pellet will be anaerobic. The so called ‘cube root growth’ of fungi is accounted for by the model in certain circumstances. The kinetics of growth predicted for the model could be tested in several ways. It is concluded that growth according to the model may lead to large differences between the metabolism of the outer and inner hyphae of pellets.