초록
<P><B>Background</B></P><P>Cellulase and hemicellulase genes in the fungus <I>Trichoderma reesei </I>are repressed by glucose and induced by lactose. Regulation of the cellulase genes is mediated by the repressor CRE1 and the activator XYR1. <I>T. reesei </I>strain Rut-C30 is a hypercellulolytic mutant, obtained from the natural strain QM6a, that has a truncated version of the catabolite repressor gene, <I>cre1</I>. It has been previously shown that bacterial mutants lacking phosphoglucose isomerase (PGI) produce more nucleotide precursors and amino acids. PGI catalyzes the second step of glycolysis, the formation of fructose-6-P from glucose-6-P.</P><P><B>Results</B></P><P>We deleted the gene <I>pgi1</I>, encoding PGI, in the <I>T. reesei </I>strain Rut-C30 and we introduced the <I>cre1 </I>gene in a Δ<I>pgi1 </I>mutant. Both Δ<I>pgi1 </I>and <I>cre1<SUP>+</SUP></I>Δ<I>pgi1 </I>mutants showed a pellet-like and growth as well as morphological alterations compared with Rut-C30. None of the mutants grew in media with fructose, galactose, xylose, glycerol or lactose but they grew in media with glucose, with fructose and glucose, with galactose and fructose or with lactose and fructose. No growth was observed in media with xylose and glucose. On glucose, Δ<I>pgi1 </I>and <I>cre1<SUP>+</SUP></I>Δ<I>pgi1 </I>mutants showed higher cellulase activity than Rut-C30 and QM6a, respectively. But in media with lactose, none of the mutants improved the production of the reference strains. The increase in the activity did not correlate with the expression of mRNA of the xylanase regulator gene, <I>xyr1</I>. Δ<I>pgi1 </I>mutants were also affected in the extracellular β-galactosidase activity. Levels of mRNA of the glucose 6-phosphate dehydrogenase did not increase in Δ<I>pgi1 </I>during growth on glucose.</P><P><B>Conclusions</B></P><P>The ability to grow in media with glucose as the sole carbon source indicated that <I>Trichoderma </I>Δ<I>pgi1 </I>mutants were able to use the pentose phosphate pathway. But, they did not increase the expression of <I>gpdh</I>. Morphological characteristics were the result of the <I>pgi1 </I>deletion. Deletion of <I>pgi1 </I>in Rut-C30 increased cellulase production, but only under repressing conditions. This increase resulted partly from the deletion itself and partly from a genetic interaction with the <I>cre1-1 </I>mutation. The lower cellulase activity of these mutants in media with lactose could be attributed to a reduced ability to hydrolyse this sugar but not to an effect on the expression of <I>xyr1</I>.</P>