Fungal morphology and fragmentation in production scale fermentation

Filamentous fungi are extensively used in fermentation industry due their ability to produce many types of chemicals and pharmaceuticals. However, many fungal fermentations suffer from the same problem—high broth viscosity that often makes agitation difficult. Since fungal morphology is the main reason for high viscosity, we believe manipulating fungal branching may be an effective way of controlling viscosity. With using a parallel-plate flow chamber coupled with microscopy and image processing system, we explored two possible ways to manipulate branching: (i) modifying nutrient (carbon and nitrogen) and (ii) addition of compounds known qualitatively effect fungal morphology. Since fragmentation also plays a role in determining fungal morphology, we assessed the degree to which a significant increase in agitation intensity in large-scale fungal fermentations, affects mycelial morphology, fragmentation behavior, and recombinant protein expression. Fed-batch fermentations were conducted in go m3 fermenters, with a recombinant strain of Aspergillus oryzae, at two different levels of impeller power (i.e., agitation intensity). We found that recombinant enzyme expression was lower in the fermentations operated at increased impeller power However, contrary to our expectations, increased impeller power did not appear to cause any more damage than found when cells were grown at lower agitation intensity. This result led us to investigate the mechanical strength of hyphal cell wall (tensile strength) during the fermentation. We used turbulent hydrodynamic theory to develop a correlation that allows experimental data of morphology and hydrodynamics to be used to estimate relative (pseudo) tensile strength (σ_pseudo) of filamentous fungi. It was found that σ_pseudo, is not constant, but varies with culture age, presumably due to differences in physiological state. To prove this, we developed a mechanical breakage test to examine the susceptibility of A. oryzae hyphae to fragmentation in shake flasks and lab scale fermenters. It was found that both medium and culture age made a difference on this susceptibility.