The saprophytic fungus Trichoderma reesei has long been used as a model to study microbial degradation of lignocellulosic biomass. The major cellulolytic enzymes of T. reesei are the cellobiohydrolases CBH1 and CBH2, which constitute more than 70% of total proteins secreted by the fungus. However, their physiological functions and effects on enzymatic hydrolysis of cellulose substrates are not sufficiently elucidated. Here, the cellobiohydrolase-encoding genes cbh1 and cbh2 were deleted, individually or combinatively, by using an auxotrophic marker-recycling technique in T. reesei. When cultured on media with different soluble carbon sources, all three deletion strains (Δcbh1, Δcbh2, and Δcbh1Δcbh2) exhibited no dramatic variation in morphological phenotypes, but their growth rates increased apparently when cultured on soluble cellulase-inducing carbon sources. In addition, Δcbh1 showed dramatically reduced growth and Δcbh1Δcbh2 could hardly grew on microcrystalline cellulose (MCC), whereas all strains grew equally on sodium carboxymethyl cellulose (CMC-Na), suggesting that the influence of the CBHs on growth was carbon source-dependent. Moreover, five representative cellulose substrates were used to analyse the influence of the absence of CBHs on saccharification efficiency. CBH1 deficiency significantly affected the enzymatic hydrolysis rates of various cellulose substrates, where acid pre-treated corn stover (PCS) was influenced the least. CBH2 deficiency reduced the hydrolysis of MCC, PCS, and acid pre-treated and delignified corncob but improved the hydrolysis ability of filter paper. These results demonstrate the specific contributions of CBHs to the hydrolysis of different types of biomass, which could facilitate the development of tailor-made strains with highly efficient hydrolysis enzymes for certain biomass types in the biofuel industry.

中文翻译：

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里氏木霉中纤维二糖水解酶基因缺失对碳源依赖性生长和木质纤维素酶水解的影响。

腐生真菌里氏木霉一直被用作研究木质纤维素生物质微生物降解的模型。里氏木霉的主要纤维素分解酶是纤维二糖水解酶CBH1和CBH2，它们占真菌分泌的总蛋白质的70％以上。然而，尚未充分阐明它们的生理功能和对纤维素底物的酶促水解的影响。在这里，通过使用里氏木霉中的营养缺陷型标记回收技术，分别或组合删除了纤维二糖水解酶编码基因cbh1和cbh2。当在具有不同可溶性碳源的培养基上培养时，所有三个缺失菌株（Δcbh1，ΔCBH2，和Δ CBH1 Δ CBH2可溶性纤维素酶诱导碳源培养时）没有表现出显着的形态学表型变化，但是它们的生长速率明显增加。此外，Δ CBH1显示出显着降低的生长和Δ CBH1 Δ CBH2几乎不能在微晶纤维素（MCC）上生长，而所有菌株在羧甲基纤维素钠（CMC-Na）上均均生长，这表明CBHs对生长的影响取决于碳源。此外，使用五个代表性的纤维素底物来分析不存在CBHs对糖化效率的影响。CBH1缺乏显着影响各种纤维素底物的酶促水解速率，其中酸预处理玉米秸秆（PCS）影响最小。CBH2缺乏症减少了MCC，PCS和酸预处理和去木质素的玉米芯的水解，但提高了滤纸的水解能力。这些结果证明了CBHs对不同类型生物质水解的特定贡献，