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Brief Incubations of Mixed Ruminal Bacteria: Effects of Anaerobiosis and Sources of Nitrogen and Carbon¹

Microbiology Division, Department of Dairy Science, University of Illinois, Urbana 61801

ABSTRACT

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 McDougall's or Starvation-survival buffer were compared for their effectiveness in preparing a mixed rumen 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 carbohydrate-specific bacterial groups and appeared to enhance growth of cellulolytic 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 bovis-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.

¹ A preliminary report of this research was presented at the 1980 annual meeting of the American Society for Microbiology, Abstract No. I 122, p. 104.

² The Upjohn Company, Agricultural Division, Kalamazoo, MI 49001.