|Gardner r g,|
|Wells j e,|
|Wilson d b,|
Submitted to: Federation of European Microbiological Societies Microbiology Letters
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/23/1994
Publication Date: N/A
Citation: Interpretive Summary: Ruminant farm animals (cattle, sheep, goats) often consume diets containing cellulose which, when digested by rumen microorganisms, helps meet the animal's energy requirements. However, the rumen microorganisms lose their capacity to digest cellulose when the diets are high in starch. Starch digestion results in a decrease in ruminal pH (increased rumen acidity) and cellulolytic (cellulose-digesting) bacteria cannot tolerate even modest decreases in pH. We have undertaken a project to convert an acid-resistant, non-cellulolytic bacterium into one that can digest cellulose at low pH. This project entails the conversion of an endoglucanase (an enzyme that can digest only soluble cellulose) into a true cellulase (an enzyme that can digest insoluble cellulose) by addition of a cellulose-binding domain. This manuscript describes the regulation of endoglucanase synthesis and characterizes its cellulolytic activity toward a number of different compounds. If this project is successful, we will be able to re-inoculate the rumen with a pH-resistant. cellulolytic bacterium and increase the rate of cellulose digestion in animals with low ruminal pH. The net result would be improved feed-use efficiency by ruminant farm animals.
Technical Abstract: The B-1,4 endoglucanase of the ruminal bacterium, P. ruminicola B14, hydrolyzed carboxymethylcellulose and barley glucan but not xylan or mannan. The endoglucanase and xylanase had distinctly different patterns of induction and repression, but the endoglucanase and mannanase had a similar type of regulation. The endoglucanase and mannanase were strongly induced by mannose, cellobiose and xylose, and these activities were at least 50-fold lower if sucrose, arabinose or rhamnose was the energy source for growth. Because sucrose and arabinose were able to conteract the induction by mannose or cellobiose, it appeared that these sugars were indeed repressors. The endoglucanase activity was also at least 2-fold lower when the cells were provided with two inducers (mannose and cellobiose). The combination of cellobiose and mannose caused a slight increase in growth rate, but the overall correlation between growth rate and endoglucanase activity was very low.