SOME NUTRITIONAL CHARACTERISTICS OF PREDOMINANT CULTURABLE RUMINAL BACTERIA

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Abstract
The effect of enzymatic hydrolysate of casein, NH4 +, a mixture of volatile fatty acids (acetic, n-valeric, isovaleric, 2-methyl-butyric, and isobutyric), hemin, and ruminal fluid on growth of 89 freshly isolated strains of predominant culturable ruminal bacteria was studied, using basal media containing glucose, cellobiose, or maltose as energy source, minerals, cysteine, and S= as reducing agents, and H2CO3- HCO3[long dash]buffer. Of these strains, 13% (four morphological groups) grew poorly or not at all in defined medium plus casein hydrolysate; 6% (one mor-phological group) required casein hydrolysate; 56% (four mor-phological groups) grew with either NH4+ or casein hydrolysate as the main source of nitrogen; and NH4 +, but not casein hydrolysate, was essential for 25% of the strains (five morphological groups). The volatile fatty acid mixture excluding acetate was essential for 19% of the strains (five morphological groups), and this mixture and acetate were necessary for good growth of 23% of the strains (one morphological group) when casein hydrolysate was excluded from the medium; 30% of the strains (one morphological group) required hemin. Similar studies are reported on 35 old laboratory strains of ruminal bacteria, most of which were previously identified. The results indicate that most strains of ruminal bacteria can be grown in defined media, and suggest the relative importance of NH4 + and volatile fatty acids and the relative lack of importance of organic nitrogen compounds such as amino acids in the nutrition of these bacteria.