Improvement of cellulosic biomass-degrading enzyme production by reducing extracellular protease production in Aspergillus aculeatus

[摘要] We investigated the effects of deleting major extracellular protease-encoding genes on cellulolytic andxylanolytic enzyme production in Aspergillusaculeatus. We first investigated the effect of prtTdeletion, a positive transcription factor for extracellular protease-encoding genes in Aspergillus, onextracellular protease production in A. aculeatus.Genetic analysis indicated that among the majorextracellular proteases, pepIIa and pepIIb are controlled by PrtT, but pepI is not. Thus, we generateda mutant with deletion of the two genes prtT andpepI (∆prtT∆pepI) and one with deletion of the threegenes pepI, pepIIa, and pepIIb (∆pepI∆IIa∆IIb).Extracellular protease activities decreased in both∆prtT∆pepI and ∆pepI∆IIa∆IIb to 3% of that in thecontrol strain (MR12). Comparative time-courseanalyses indicated that endoglucanase activity in∆prtT∆pepI increased to double that in MR12.Xylanase activities increased in both ∆prtT∆pepIand ∆pepI∆IIa∆IIb to fourfold higher than that inMR12 at maximum. β-Glucosidase activities wereincreased in ∆prtT∆pepI and ∆pepI∆IIa∆IIb 1.3- and1.4-fold higher than that in MR12 at maximum,respectively. Residual activities of endoglucanase,xylanase, and β-glucosidase after 7 days of incubation at 37°C in the culture supernatant were 63%,36%, and 48% of the original in MR12. Residualendoglucanase activities were more than 80% of theoriginal in ∆prtT, ∆prtT∆pepI, and ∆pepI∆IIa∆IIb.Residual xylanase activities were not improved inall test strains. β-Glucosidase remained almost 97%of the original in ∆prtT∆pepI. These findings indicated that the reduction of extracellular proteaseseffectively improved cellulolytic and xylanolyticenzyme production and stability in A. aculeatus.

[学科分类] 微生物学和免疫学

[关键词] enzyme production;gene regulation;protease