居瘤胃解纤维素菌细胞密度与纤维素酶的合成

Cell density mediated cellulases synthesis in Cellulosilyticum ruminicola

居瘤胃解纤维素菌(Cellulosilyticum ruminicola)H1是本实验室分离自青海牦牛瘤胃的一株新的纤维素降解细菌。前期研究发现,菌株H1在滤纸纤维素上连续传代数次后无法生长,只有在纤维素降解产物纤维二糖中培养后方能继续在纤维素中生长,并恢复其纤维素降解活性。这与纤维素酶合成受"代谢产物抑制"的传统认识相悖。【目的】证明菌株H1的纤维素酶合成受细胞密度调控。【方法】检测菌株H1的纤维素酶活和转录水平在高和低密度细胞培养物中差异,并检测高密度细胞培养物中的寡肽对低密度细胞纤维素酶活和转录水平的促进作用。【结果】菌株H1的高密度细胞培养物的纤维素酶活和转录水平比低密度细胞的高3-10倍;并且高密度细胞培养液能显著提高低密度细胞纤维素酶活和转录水平。【结论】居瘤胃解纤维素菌(Cellulosilyticum ruminicola)H1纤维素酶的合成受细胞密度调控。

Cellulosilyticum ruminicola H1 is an anaerobic cellulolytic bacterium isolated from the rumen content of yak.Previously,we found that strain H1 lost growth on filter paper cellulose after several subcultures.The growth on cellulose cannot be restored until a few transfers in the cellobiose-containing medium.This is contrary to the knowledge that microbial cellulases synthesis is induced by the substrate while repressed by the metabolites,e.g.cellobiose,but provides a hint of cell-density mediated cellulase synthesis.[Objective] The study aimed to test if cell density regulation mechanism involved in the cellulase synthesis by Cellulosilyticum ruminicola H1.[Methods] By using enzyme assays and real-time PCR quantification,we investigated cellulase activities and the gene transcript levels in the high-and low-cellmass cultures of strain H1.We also determined the elevation of endoglucanase and cellobiohydrolase activities and the gene expression in the low-cellmass culture upon addition of the high-cellmass spent culture.[Results] Both endoglucanase and cellobiohydrolase of strain H1 were detected 3 to 10 times higher in the high cellmass culture than in the lower cellmass culture either in enzymatic activity or the gene transcript abundance,thus confirming the cell density-mediated cellulase synthesis.[Conclusion] This study demonstrates that cell density regulation is involved in cellulases synthesis by Cellulosilyticum ruminicola H1.