Xylanase Induction by L-Sorbose in a Fungus, Trichoderma reesei PC-3-7

Xylanase induction by L-sorbose was studied in a resting cell system of a filamentous fungus, Trichoderma reesei PC-3-7, a hypercellulolytic mutant, and compared with that by other inducers. L-Sorbose induced xylanase activity as well as cellulase. It induced a higher level of xylanase activity than sophorose and xylose did. Three main xylanases, xylanase I (Xyn I), xylanase II (Xyn II), and a non-specific endoglucanase I (EG I), were separated using cation-exchange chromatography, and their activity were measured. Xyn II was induced in about the same proportion (60-80% of the total xylanase activity) by all inducers used. On the other hand, Xyn I was apparently induced by L-sorbose, xylose, and xylooligosaccharides, but only a little by sophorose. Northern blot analysis showed that L-sorbose induced Xyn I and Xyn II at the transcriptional level, and more xyn1 mRNA was transcribed after L-sorbose addition than after sophorose. These results suggested that the expressions of both Xyn I and Xyn II are regulated, at least in part, in a different manner. Furthermore, the Xyn I induction by L-sorbose indicated that an unknown common regulatory mechanism may exist between Xyn I and cellulase inductions.