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Microb Cell Fact. 2011 May 24;10:40. doi: 10.1186/1475-2859-10-40.
Cellulase and hemicellulase genes in the fungus Trichoderma reesei are repressed by glucose and induced by lactose. Regulation of the cellulase genes is mediated by the repressor CRE1 and the activator XYR1. T. reesei strain Rut-C30 is a hypercellulolytic mutant, obtained from the natural strain QM6a, that has a truncated version of the catabolite repressor gene, cre1. 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.
We deleted the gene pgi1, encoding PGI, in the T. reesei strain Rut-C30 and we introduced the cre1 gene in a Δpgi1 mutant. Both Δpgi1 and cre1+Δpgi1 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, Δpgi1 and cre1+Δpgi1 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, xyr1. Δpgi1 mutants were also affected in the extracellular β-galactosidase activity. Levels of mRNA of the glucose 6-phosphate dehydrogenase did not increase in Δpgi1 during growth on glucose.
The ability to grow in media with glucose as the sole carbon source indicated that Trichoderma Δpgi1 mutants were able to use the pentose phosphate pathway. But, they did not increase the expression of gpdh. Morphological characteristics were the result of the pgi1 deletion. Deletion of pgi1 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 cre1-1 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 xyr1.
里氏木霉中的纤维素酶和半纤维素酶基因受葡萄糖抑制，受乳糖诱导。纤维素酶基因的调控由抑制剂 CRE1 和激活剂 XYR1 介导。里氏木霉 Rut-C30 菌株是一种超纤维素酶突变体，它是从天然菌株 QM6a 中获得的，具有截短的分解代谢抑制剂基因 cre1。先前的研究表明，缺乏磷酸葡萄糖异构酶（PGI）的细菌突变体产生更多的核苷酸前体和氨基酸。PGI 催化糖酵解的第二步，将葡萄糖-6-P 转化为果糖-6-P。
我们在里氏木霉 Rut-C30 菌株中删除了编码 PGI 的基因 pgi1，并在 Δpgi1 突变体中引入了 cre1 基因。与 Rut-C30 相比，Δpgi1 和 cre1+Δpgi1 突变体的生长和形态都发生了变化，呈颗粒状。突变体在含有果糖、半乳糖、木糖、甘油或乳糖的培养基中均不生长，但在含有葡萄糖、果糖和葡萄糖、半乳糖和果糖或乳糖和果糖的培养基中生长。在含有木糖和葡萄糖的培养基中，没有观察到生长。在葡萄糖上，Δpgi1 和 cre1+Δpgi1 突变体的纤维素酶活性均高于 Rut-C30 和 QM6a。但是在含有乳糖的培养基中，没有一个突变体提高了对照菌株的产量。活性的增加与木聚糖酶调节基因 xyr1 的 mRNA 表达无关。Δpgi1 突变体的细胞外β-半乳糖苷酶活性也受到影响。在 Rut-C30 生长过程中，Δpgi1 中的葡萄糖 6-磷酸脱氢酶 mRNA 水平并没有增加。
能够在以葡萄糖为唯一碳源的培养基中生长表明，里氏木霉 Δpgi1 突变体能够利用戊糖磷酸途径。但是，它们没有增加 gpdh 的表达。形态特征是 pgi1 缺失的结果。在 Rut-C30 中删除 pgi1 增加了纤维素酶的产量，但仅在抑制条件下。这种增加部分是由于删除本身，部分是由于与 cre1-1 突变的遗传相互作用。这些突变体在含有乳糖的培养基中较低的纤维素酶活性可能归因于其水解这种糖的能力降低，但不是由于对 xyr1 的表达的影响。
