Ethanol fermentation by saprotrophic white-rot fungus Phanerochaete sordida YK-624 during wood decay as a system for short-term resistance to hypoxic conditions

In this study, major factors involved in regulating ethanol production from wood by the saprotrophic white-rot fungus Phanerochaete sordida YK-624 were investigated. P. sordida YK-624 produced ethanol from wood meal culture without the addition of any nutrients, and ethanol was produced from wood culture only when the oxygen concentration in headspace was reduced to ≤5%; thereafter, ethanol production ceased within a few days. Analyses of gene expression during aerobic incubation indicated that P. sordida simultaneously upregulates the glycolytic pathway from sugar uptake to pyruvate conversion during ethanol fermentation and suppresses pyruvate influx into the TCA cycle. Upon termination of ethanol fermentation, the expression of all tested genes was repressed, and the fungus ceased to grow. In contrast, the fungus could utilize ethanol for aerobic growth. These results suggest that ethanol fermentation by P. sordida functions as a short-term stress response system under anaerobic conditions during wood decay, enabling the fungus to rapidly resume growing when oxygen is supplied (e.g., following breakdown of plant cell walls or removal of the fungus from water immersion). This is the first report to describe the physiologic significance of ethanol fermentation in saprotrophic white-rot fungi.

Draft Genome Sequence of the White-Rot Fungus Phanerochaete sordida YK-624

Here, we report the draft genome sequence of the white-rot basidiomycete fungus Phanerochaete sordida YK-624 (ATCC 90872), which was isolated in Yakushima, Kagoshima, Japan. The genome of this strain was found to be 41.2 Mbp, with a G+C content of 58.7%, and to comprise 17,108 predicted protein-coding sequences.

Improvement of saccharide yield from wood by simultaneous enzymatic delignification and saccharification using a ligninolytic enzyme and cellulase

White-rot fungi are thought to hold promise for development of a delignification pretreatment process for wood biorefinery that is less energy-consuming than current processes. However, the reaction must take place over weeks and consumes non-neglectable amounts of saccharides. To establish a biological process for wood biorefinery would first require establishment of an enzymatic approach to delignification. Such an approach has the potential to lower costs and reduce saccharide loss. Here, we attempted enzymatic delignification reactions using manganese peroxidases (MnP), a lignin-degrading enzyme, under several reaction conditions. The delignification rate from beech wood meal (particle size <45 μm) of up to 11.0% in 48 h was reached in a MnP reaction supplemented with multiple co-oxidants, glucose, glucose oxidase (GOD) and commercial cellulase. An additional 48-h reaction using fresh MnP/co-oxidants increased the delignification rate to 14.2%. Simultaneous enzymatic delignification and saccharification, which occurs without a need for glucose supplementation, successfully improved the glucose yield to 160% of the reaction without MnP. Development of a more accurate imitation of the mechanisms of delignification that occurs in white-rot fungi has the potential to improve the monosaccharide yield resulting from simultaneous delignification and saccharification.

Self-fusion and fusion cell isolation of transformants derived from white rot fungus Phanerochaete sordida YK-624 by simple visual method

In order to develop a simple method for crossing two transformants, we first attempted to elucidate the fusion type (self-compatibility or -incompatible) of Phanerochaete sordida YK-624. Two transformants expressing green or red fluorescent protein derived from an auxotrophic mutant were constructed. Each recombinant protein fluoresced by expression as a fused protein with glyceraldehyde-3-phosphate dehydrogenase. On co-culture of both transformants, a number of sequential hyphal cells emitting dual fluorescence were formed at the contact areas of both hyphae. Some of the single cells isolated as protoplasts and chlamydospore from the co-cultures also expressed these fluorescent proteins. These results suggest that P. sordida YK-624 possesses a self-compatible fusion system. In addition, transformant strains with different fluorescence derived from this fungus can readily undergo self-fusion and nuclear interchange events by confrontational and mixed cultivation, and we developed a simple method that allows fused cells to be isolated as chlamydospores.