# Characterization of strain degeneration in the RL-P37 strain lineage of Trichoderma reesei

## TL;DR

This study examines how a high-cellulase-producing fungus, Trichoderma reesei, loses productivity over time and identifies morphological changes that could help monitor strain stability in industry.

## Contribution

The study characterizes strain degeneration in the RL-P37 lineage of T. reesei, revealing morphological indicators linked to productivity loss.

## Key findings

- RL-P37 and its descendant GEN-3A show spontaneous loss of cellulase productivity during prolonged use.
- Degenerated isolates exhibit reduced cellulase productivity, altered growth, and distinct morphological changes.
- Bulbous, highly branched hyphae are associated with high cellulase production but are lost in degenerated strains.

## Abstract

Spontaneous strain degeneration, defined as the loss of an essential biological function during prolonged usage, is frequently observed in microorganisms and poses a significant challenge to the biotechnology industry. In Trichoderma reesei, a filamentous fungus widely used for large-scale cellulase production, spontaneous loss of cellulase productivity has been reported. However, studies on this phenomenon have focused solely on industrial strains derived from the Rut-C30 lineage. This study analyzes strain degeneration in a different industrial lineage of T. reesei, RL-P37, and its hypercellulase-producing descendant, GEN-3A. We found that RL-P37 and GEN-3A are also affected by the degeneration phenomenon, with the highly productive GEN-3A showing greater susceptibility. The degenerated phenotype was characterized by reduced cellulase productivity, altered growth behavior, and distinct morphological changes. In particular, cellulase hyperproduction was associated with bulbous, highly branched hyphae, while these morphological traits were lost in degenerated isolates. Our study establishes a framework for characterizing strain degeneration in T. reesei, highlights the trade-off between productivity and stability, and identifies distinctive morphological signatures linked to cellulase hyperproduction and degeneration, which may serve as early phenotypic indicators for industrial strain monitoring.