초록
<P><B>Background</B></P><P>The filamentous fungus <I>Trichoderma reesei</I> (anamorph of <I>Hypocrea jecorina</I>) displays increased cellulase expression while growing on inducers such as lactose or cellulose. However, the mechanism of cellulase induction in <I>T. reesei</I> is not yet completely characterized. Here, a protein annotated as β-glucosidase (BGL3I) was found to be involved in cellulase induction in <I>T. reesei</I>. The effects of BGL3I on cellulase production have not yet been fully understood.</P><P><B>Results</B></P><P>Deletion of the <I>bgl3i</I> gene had no influence on the growth of <I>T. reesei</I>, but significantly increased its cellulase activities. Deletion of <I>bgl3i</I> also resulted in decreased extracellular galactosidase activity, but significantly increased transcription of lactose permeases, which might be involved in lactose transport. Furthermore, deletion of <I>bgl3i</I> enhanced the transcription levels of intracellular β-glucosidases <I>cel1a, cel1b</I> and the regulator <I>xyr1</I>, which are all essential for lactose induction in <I>T. reesei</I>. BGL3I was found to have a relatively high ability to hydrolyze sophorose, which is proposed to be the strongest natural inducer of cellulase synthesis in <I>T. reesei</I>.</P><P><B>Conclusions</B></P><P>BGL3I may take part in the complex regulating system of cellulase induction. The deletion of <I>bgl3i</I> offers a new strategy to improve <I>T. reesei</I> strain performance.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (10.1186/s13068-018-1314-6) contains supplementary material, which is available to authorized users.</P>