Effect of Diet on Amino and Nucleic Acids of Rumen Bacteria and Protozoa

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Abstract
Amino acid composition and nucleic acid content of pure cultures of rumen bacteria (17 spp.) [Ruminococcus albus, Succinomonas amylolytica, Veillonella alcalescens, Megasphaera elsdenii, Selenomonas lactilytica, Succinivibrio dextrinosolvens, Anaerovibrio lipolytica, Selenomonas ruminantium, Bacteroides amylophilus, Lachnospira multiparus, B. succinogenes, Butyrivibrio fibrisolvens, Eubacterium cellulosolvens, Lactobacillus vitulinus, L. ruminis, R. flavefaciens and Streptococcus bovis] were analyzed. Amino acid composition between gram-positive and -negative organisms was not different. The total N content of gram-negative bacteria (10.8%) was significantly higher than gram-positive organisms (9.9%). DNA N:total N (mg/g) differed between gram-positive (8.8) and gram-negative (18.9) bacteria, but there was no significant difference in ratio of RNA-N to total N. In a 2nd experiment, 6 rumen-fistulated cattle were fed either a high roughage (85% alfalfa hay plus 15% concentrate) or high concentrate diet (15% alfalfa hay and 85% concentrate). Cattle were adapted 14 days and rumen contents sampled on 3 consecutive days. N content was higher in protozoa from cattle fed low concentrate (8.4%) than in protozoa from cattle fed high concentrate (7.9%) but was similar in bacteria for both diets. DNA-N:total N (mg/g) in bacteria decreased from 27.2 in cattle fed the low concentrate diet to 20.9 in those fed the high concentrate diet. Differences between sampling days were significant for both bacteria and protozoa for ratio of DNA-N to total N but were significant only in protozoa for ratio of RNA-N to total N. RNA may serve as a marker for estimating microbial production in the rumen if sources of variation are recognized and corrected adequately.