Degradation of starch granules by some amylolytic bacteria from the rumen of sheep

Publisher Website
Google Scholar
Abstract
Extracellular [alpha]-amylases from Streptococcus bovis and Clostridium butyricum, and the intracellular-amylase systems of mixed rumen bacteria, were examined for their action on starch granules. The extracellular a-amylases of S. bovis and C. butyricum rapidly degraded maize-starch granules, and some preparations of S. bovis [alpha]-amylase slowly hydrolyzed potato-starch granules. The purified amylases had the same ability to hydrolyze maize-starch granules as the cell-free filtrates from which they were prepared; potato-starch granules were not degraded. The S. bovis and C. butyricum [alpha]-amylases behaved in a manner similar to salivary [alpha]-amylase in their hydrolytic action on maize-starch granules and in their adsorption on the starch granules at 0[degree]. The C. butyricum [alpha]-amylase did not hydrolyze maltotriose but was active towards maltotetraose when a high concentration of enzyme was present. The S. bovis [alpha]-amylase could hydrolyze maltotriose, only at a high concentration. With both enzymes the apparent limit of hydrolysis of dissolved starch could be raised by the addition of larger amounts of enzyme. The intracellular-amylase systems of mixed rumen bacteria from a sheep fed on a high-grain diet and deficient in ciliate protozoa degraded potato-starch granules at a comparable rate to maize-starch granules when mineral phosphate was present. An amylase of wide specificity was obtained from mixed rumen bacteria from the grain-fed sheep when large numbers of ciliate protozoa were present. The amylase had little action on starch granules and was not adsorbed on the granules at 0[degree]. Maltotriose was hydrolyzed almost as rapidly as amylose, and glucose and maltose were the only low-molecular-weight products of starch hydrolysis. Because of the greatly decreased ability of the bacterial fraction to degrade starch granules when Entodinium spp. were present, these protozoa may take over this function from the bacteria.