A Kinetic Study of the Colony Growth of Streptomyces coelicolor A3(2) and J802 on Solid Medium

Abstract

Summary: Colony growth kinetics of Streptomyces coelicolor A3(2), the wild-type strain, and J802, a mutant incapable of utilizing agar as the sole carbon and energy source, have been studied on solid medium. General features comparable to colony growth of filamentous fungi were observed in both streptomycete strains. Hyphal frequency at the margins of colonies was assessed as the number of hyphae crossing an are of defined length and increased in an exponential manner with distance from the margin, reaching a maximum at approximately 200 μm. Aerial hyphal initials were formed approximately 350 μm from the margin. Colony radial extension was linear, but in the wild-type strain grown at low medium depths, growth was sometimes multiphasic, with successive phases of linear growth each exhibiting a slower radial growth rate than that of the preceding phase. Hyphal frequency at the colony margin decreased as colony diameter increased, indicating significant changes in environmental conditions in the peripheral growth zone during colony growth. In the primary phase of linear growth, the colony radial growth rate of both strains was independent of medium depth and in the absence of a cellophane membrane was independent of glucose concentration. Colony radial growth rate of strain J802 growing on a cellophane underlay increased with glucose concentration. Hyphal frequency of strain A3(2) increased gradually with medium depth but was independent of glucose concentration. In strain J802, hyphal frequency exhibited a strong dependence on both medium depth and glucose concentration. A threshold glucose concentration for growth was not found and inhibition of strain A3(2) occurred above 1 gl−1. The results agree with many aspects of accepted theories for colony growth of both unicells and filamentous fungi, but suggest production of staling products and/or secondary metabolites to be of equal significance to nutrient limitation in controlling colony development.