An attempt to construct superior Trichoderma reesei F418 isolate for enhancing xylanase production from alkali pretreated rice straw (RS) under solid state fermentation (SSF) was conducted. Mutagenesis for T. reesei F418 in conjugation with intra-specific protoplast fusion between the selected mutants was applied to obtain hyperproducing strains. After mutagenesis by UV-irradiation, 70 mutants were recovered. Twenty eight mutants produced higher xylanase activity than the wild type (WT) with fold increase ranged from 1.1 to 2.94. Mutant Co-6 is the highest enzyme producer. According to heavy metals response, intraspecific protoplast fusion between the selected hyperproducing mutant isolates was carried out using polyethylene glycol (PEG)-6000. The fusant C6b/1 was found to be stable and the promising fusant isolate for xylanase production from alkali pretreated RS (6875 IU/gDW) and untreated RS (4122 IU/gDW) with 308% and 184.6% higher productivity, respectively, than the WT strain. The application of mutagenesis in conjunction with protoplast fusion is good and effective tools for improvement of T. reesei F418 for enhancing xylanase productivity from untreated and alkali-pretreated RS under SSF conditions.
Key words: Trichoderma, Xylanase, Rice straw, UV-mutants, Protoplast fusion, Stability
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