Brief Incubations of Mixed Ruminal Bacteria: Effects of Anaerobiosis and Sources of Nitrogen and Carbon

A series of brief in vitro incubations with mixed rumen bacterial populations was conducted.Aerobic, aerobic plus cysteine-sulfide, and anaerobic plus cysteine-sulfide treatments using either Mc-Dougall's or Starvation-survival buffer were compared for their effectiveness in preparing a mixed tureen bacterial inoculum from rumen contents.The results showed that the absence of strict anaerobiosis resulted in partial loss of cellulolytic and amylolytic bacterial groups.In incubations containing a mixture of carbohydrates and various nitrogen sources, urea plus acid-hydrolyzed casein was the best for maintaining normal proportions of carbohydratespecific bacterial groups and appeared to enhance growth of ceUulolytic and xylanolytic groups.With urea plus acid-hydrolyzed casein as the nitrogen source, effects of individual carbohydrate sources were monitored.Glucose, cellobiose, and soluble starch incubations were predominated by Streptococcus boris-like bacteria within 3 h and resulted in disappearance of the cellulolytic bacterial group.In contrast, pectin or xylan plus xylose as carbon sources allowed a normal, rumen-like fermentation to continue and enhanced growth of cellulolytic and xylanolytic groups.The importance of these findings in relation to research with mixed ruminal bacteria is discussed.