Normal Flora—Rumen Bacteria

Abstract

The digestion of feeds, which usually contain large amounts of cellulose and similar polysaccharides, by the ruminant animal is largely dependent on an intense anaerobic microbial fermentation in the rumen. Nonsporeforming anaerobic bacteria are mainly responsible for the fermentation. The carbohydrates of the diet are fermented mainly to acetate, propionate, butyrate, CO₂, and CH₄, and these volatile acids are a major source of energy for the ruminant animal. Major extracellular intermediates, i.e., products of some microbial species that are utilized by others in the fermentation of polysaccharides include oligosaccharides and sugars, H₂, formate, succinate and, under some conditions, lactate. Microbial protein from the rumen is usually the chief source of essential amino acids for the ruminant regardless of the type of protein in the diet and most species of rumen bacteria can utilize ammonia as the main nitrogen source. The microorganisms also metabolize dietary lipids and synthesize B-vitamins. The methods of culture and some taxonomic, nutritional, and metabolic characteristics of some representative rumen anaerobic bacteria are briefly discussed. These bacteria, in general, are better characterized and their functions better understood than those of any other anaerobic habitat.