Effects of Condensed Tannins on Endoglucanase Activity and Filter Paper Digestion by Fibrobacter succinogenes S85 †

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The effect of condensed tannins from birdsfoot trefoil (Lotus corniculatus L.) on the cellulolytic rumen bacterium Fibrobacter succinogenes S85 was examined. Condensed tannins inhibited endoglucanase activity in the extracellular culture fluid, at concentrations as low as 25 μg ml-1. In contrast, cell-associated endoglucanase activity increased in concentrations of condensed tannins between 100 and 300 μg ml-1. Inhibition of endoglucanase activity in both the extracellular and the cell-associated fractions was virtually complete at 400 μg of condensed tannins ml-1. Despite the sharp decline in extracellular endoglucanase activity with increasing concentrations of condensed tannins, filter paper digestion declined only moderately between 0 and 200 μg of condensed tannins ml-1. However, at 300 μg ml-1, filter paper digestion was dramatically reduced and at 400 μg ml-1, almost no filter paper was digested. F. succinogenes S85 was seen to form digestive grooves on the surface of cellulose, and at 200 μg ml-1, digestive pits were formed which penetrated into the interior of cellulose fibers. Cells grown with condensed tannins (100 to 300 μg ml-1) possessed large amounts of surface material, and although this material may have been capsular carbohydrate, its osmiophilic nature suggested that it had arisen from the formation of tannin-protein complexes on the cell surface. The presence of electron-dense extracellular material suggested that similar complexes were formed with extracellular protein.

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