Adaptation of an In Vitro System to the Study of Starch Fermentation by Rumen Bacteria

Publisher Website
Google Scholar
Abstract
An in vitro system was described for the study of starch fermentation by microorganisms from the rumen of sheep fed a high grain diet. A centrifugal procedure was used to obtain the predominant rumen bacteria as a sediment which appeared to proliferate in vitro without gross changes in morphological types. Under the conditions of these experiments the maximal starch fermentation occurred when flask contents were readjusted to pH 6.8. The addition of biotin and p-aminobenzoic acid or autoclaved rumen fluid supernatant was not necessary for maximal starch fermentation. Eighteen mixed cultures from the rumen of three sheep fed identical diets were compared and found to be similar in the relationships between the production of total volatile fatty acid or the synthesis of trichloroacetic acid-insoluble nitrogen and the extent of starch fermentation. Differences in the amount of starch fermented in a given time were apparently the result of differences in the time required to reach the maximal rate of fermentation and to differences in the maximal rates of fermentation. These differences were not consistent with respect to sheep or to trials. There appeared to be two types of fermentations in vitro related to the maximal rates of fermentation attained. Accumulation of lactate was associated with the higher rates of fermentation. Possible explanations for this phenomenon are suggested including the effect of a cyclic pH variation on the metabolic pathways of fermentation.