Identifying the conditions for development of beneficial mycelium morphology for chitosan-producing Absidia spp. in submersed cultures

Abstract

The first step when producing chitosan from fungi grown submersed, i.e. the cultivation technique of some chitosan-producing Abisidia spp/, was studied. Various strains have their own specific requirements for development of morphology beneficial for a high growth rate. Regarding the species studied (A. coerulea, CBS 100.38; A. fusca, CBS 102.35; A. glauca, Dep. Microbial Ecology, Lund; A. repens; CBS 102.32), these demands are primarily those concerning agitation. Increasing the number of spores (from 1.4·107 to 5.8·107 per liter) of A. coerulea increased the initial growth rate, which on the other hand (due to agglomeration of pellets) levelled off at a comparatively earlier stage. Too low stirrer speed generally caused the formation of a pulp with a strong decline in growth rate. Elevated stirrer speeds caused the formation of a more compact morphology, often in the form of small pellets. The use of an open paddle impeller with a large diameter (with satisfactory pumping and mixing characteristics) ran at a sufficiently high stirrer speed to avoid the formation of a viscous pulp allowed most of the species to grow satisfactorily. Continuous cultivations were hard to establish due to lack of new growth spots and accreted growth.