Screening Trichoderma reesei for low viscosity phenotypes

Trichoderma reesei is a filamentous fungus that is an important host for industrial enzyme production due to its hyper-secretion capabilities. The enzymes produced are used in many industries including, textile, animal feed, food, and biofuel production. The productivity of commercial filamentous fungal fermentations is limited by the need to restrict cell mass concentrations due to high broth viscosity and the resulting limitations to oxygen transfer. Morphological mutants are useful in reducing broth viscosity and improving the distribution of oxygen and nutrients. This enables higher cell density fermentations resulting in improved volumetric productivity. Strain improvement screens were developed to select for morphology mutants with short or highly branched hyphal morphology. Causative mutations responsible for the lower broth viscosity phenotypes were identified from mutants using genome re-sequencing or insertional mutagenesis. Most of these genes were found to have functions related to the cell wall or to the stress response. In many cases, these mutations could be combined to further reduce broth viscosity.