Summary auto-generated
This study examined strain improvement for lignin degradation in the white rot fungus Phanerochaete chrysosporium through selective breeding without mutagenesis. Researchers used the diploid strain ME446, which carries abundant genetic markers (RFLPs), to generate meiotic progeny, heterokaryotic crosses, and secondary derivatives. Lignin mineralization was measured using radiolabeled synthetic lignin model (14C-DHP) and plant lignocellulose substrate. Under optimized conditions (DMS buffer, 2% glucose, static culture), manganese peroxidase (MnP) was detected but lignin peroxidase (LIP) was not, indicating LIP activity is not a valid assay for lignin degradation. Among 26 homokaryotic progeny, mineralization performance varied 70-fold, with some strains outperforming the parent ME446. Performance did not correlate with any single RFLP allele among 38 tested markers, suggesting multiple genes contribute to lignin mineralization. Heterokaryotic strains and their meiotic progeny showed narrower performance ranges than initial progeny, consistent with polygenic control. Scanning electron microscopy confirmed significant structural degradation of lignocellulose. These results demonstrate that lignin mineralization performance can be improved through cycles of crossing and fruiting without mutagenesis, providing a model for informed strain improvement programs.
Key findings
- Manganese peroxidase (MnP) but not lignin peroxidase (LIP) was detectable under optimized lignin mineralization conditions, indicating LIP activity is not a valid assay for lignin degradation
- Lignin mineralization performance among 26 homokaryotic progeny varied 70-fold, demonstrating substantial variation suitable for strain improvement
- No correlation was found between lignin mineralization performance and any single RFLP allele among 38 tested genetic markers, indicating polygenic control of this trait
- Strain improvement through selective breeding and crossing is achievable without mutagenesis, with some progeny outperforming the parental strain ME446
- Performance variation narrowed in heterokaryotic and secondary homokaryotic strains compared to initial meiotic progeny, consistent with multi-genic inheritance
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Abstract
Summary: The effect of breeding from the white rot fungus Phanerochaete chrysosporium ME446 on performance for lignin mineralization was examined. This model for informed strain improvement without mutagenesis is based on abundant restriction fragment length polymorphisms (RFLPs). Under optimized conditions for lignin mineralization, extracellular manganese peroxidase (MnP) but not lignin peroxidase (LiP) could be detected, so measurement of LiP activity is not a valid assay for lignin degradation. Mineralization of 14C-labelled synthetic lignin (14C-DHP) was used to compare the performance of the wild-type strain ME446 with those of sets of progeny strains. Meiotic progeny from strain ME446, heterokaryotic progeny of crosses between such strains, and meiotic progeny of one heterokaryotic strain were examined. In each case, a minority of strains performed more efficiently than the parental strain ME446. The greatest range of lignin-mineralization performance (70-fold) was found within the set of initial progeny of ME446 and the narrowest was within the set of secondary homokaryotic strains. This is consistent with the view that a moderate number of determinants contribute to lignin mineralization performance. However, performance did not correlate with the possession of any single allele of those for 38 previously defined RFLP markers. The results show that lignin mineralization performance can be improved by cycles of crosses and fruiting, without mutagenesis.