Strain improvement of Trichoderma spp. through two-step protoplast fusion for cellulase production enhancement

Abstract

Fungal protoplast fusion is an approach to introduce novel characteristics into industrially important strains. Cellulases, essential enzymes with a wide range of biotechnological applications, are produced by many species of the filamentous fungi Trichoderma. In this study, a collection of 60 natural isolates were screened for Avicel and carboxymethyl cellulose degradation, and two cellulase producers of Trichoderma virens and Trichoderma harzianum were used for protoplast fusion. One of the resulting hybrids with improved cellulase activity, C1-3, was fused with the hyperproducer Trichoderma reesei Rut-C30. A new selected hybrid, F7, was increased in cellulase activity 1.8 and 5 times in comparison with Rut-C30 and C1-3, respectively. The increases in enzyme activity correlated with an upregulation of the cellulolytic genes cbh1, cbh2, egl3, and bgl1 in the parents. The amount of mRNA of cbh1 and cbh2 in F7 resembled that of Rut-C30 while the bgl1 mRNA level was similar to that of C1-3. AFLP (amplified fragment length polymorphism) fingerprinting and GC–MS (gas chromatography – mass spectrometry) analysis represented variations in parental strains and fusants. In conclusion, the results demonstrate that a 3-interspecific hybrid strain was isolated, with improved characteristics for cellulase degradation and showing genetic polymorphisms and differences in the volatile profile, suggesting reorganizations at the genetic level.