Nutritional Interdependence Among Rumen Bacteria, Bacteroides amylophilus, Megasphaera elsdenii , and Ruminococcus albus

Abstract

Nutritional interdependence among three representatives of rumen bacteria, Bacteroides amylophilus, Megasphaera elsdenii , and Ruminococcus albus , was studied with a basal medium consisting of minerals, vitamins, cysteine hydrochloride, and NH 4 + . B. amylophilus grew well in the basal medium supplemented with starch and produced branched-chain amino acids after growth ceased. When cocultured with B. amylophilus in the basal medium supplemented with starch and glucose, amino acid-dependent M. elsdenii produced an appreciable amount of branched-chain fatty acids, which are essential growth factors for cellulolytic R. albus . A small addition of starch (0.1 to 0.3%) to the basal medium containing glucose and cellobiose brought about successive growth of the three species in the order of B. amylophilus, M. elsdenii , and R. albus , and successive growth was substantiated by the formation of branched-chain amino acids and fatty acids in the culture. Supplementation with 0.5% starch, however, failed to support the growth of R. albus . On the basis of these results, the effects of supplementary starch or branched-chain fatty acids on cellulose digestion in the rumen was discussed.