Insights into the morphology-productivity relationship of filamentous fungi through small-scale cultivation and automated microscopy of Thermothelomyces thermophilus.

Abstract

Filamentous fungi are a cornerstone in the biotechnological production of enzymes, proteins, and organic acids. However, challenges in understanding and controlling the relationship between morphology and productivity can limit their application. This study addresses these challenges using Thermothelomyces thermophilus, a promising thermophilic fungus known for the production of thermostable enzymes. We investigated the effects of environmental conditions on fungal morphology and enzyme production using a combination of microbioreactor cultivation, automated liquid handling, and automated microscopy. Specifically, batch and fed batch cultivations were performed at different pH levels and glucose feeding rates to study their effects on secretory phytase production, fungal growth, and morphology. Results from batch cultivations revealed a two-fold higher phytase activity at pH 5.5 compared to pH 6.5, with notably smaller fungal fragments at the end of cultivation. Conversely, fed batch cultivations at a feeding rate of 1 g (l h)^-1 glucose showed a 1.6-fold higher enzyme activity at pH 5.5, accompanied by much larger fungal aggregates throughout the feeding phase. These findings suggest that large aggregates are associated with high productivity; however, their breakdown further enhances enzyme release, increasing activity in the supernatant. This study not only provides insights on the morphology-productivity relationship of T. thermophilus, but also demonstrates the efficacy of integrating microbioreactors with automated microscopy. This methodology represents a significant advance in the field of fungal biotechnology, paving the way for more efficient industrial bioprocesses.