Submitted to: Current Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/15/2004
Publication Date: 5/15/2005
Citation: Fields, M.W., Russell, J.B. 2005. Transcriptional regulation of b-glucanase activity in the ruminal bacterium, prevotella bryantii b14. Current Microbiology. 50:155-159. Interpretive Summary: In ruminant animals (e.g. cattle) feed stuffs are fermented in the rumen prior to gastric and intestinal digestion, and this fermentation gives them the capacity to utilize materials that would otherwise be indigestible. Because the feed is primarily large polymers, the bacteria must produce extracellular enzymes to degrade the feed. Until recently little was known about these extracellular enzymes, but previous worked indicated that the B-glucanase of the ruminal bacterium, Prevotella bryantii was catabolite repressed by glucose. P. bryantii is a very common ruminal bacterium, but it does not have the two common mechanisms of catabolite repression, namely cyclic AMP or a phosphotransferase system. In this manuscript we show that the catabolite repression is mediated at by a decrease in gene transcription. Research on rumen microbiology has the potential to improve the efficiency of ruminal fermentation and decrease the cost of cattle production.
Technical Abstract: The ruminal bacterium, Prevotella bryantii B14 cultures grew more rapidly with glucose as an energy source than mannose (0.73 versus 0.47 h-1 ), the cells and had 8-fold less B-glucanase activity (50 versus 400 nmol reducing sugar mg protein-1 min-1). Cultures that were provided with glucose and mannose had little B-glucanase activity even though both sugars were utilized. The observation glucose and mannose were utilized simultaneously indicated that B-glucanase expression was not merely a simple induction or inducer exclusion. When glucose was added to cultures growing on mannose, hexose flux through the glucomannokinase increased 1.5 fold, and this increase was associated with an almost immediate decrease in B-glucanase mRNA. After only 3 generations times, the amount B-glucanase mRNA was comparable to that observed in cells growing only with glucose. These results indicate that B-glucanase activity is transcriptionally regulated. However, further will be needed to define more precisely define the nature of this regulation and to identify the 'immediate' in this response.