Esterase activities in Butyrivibrio fibrisolvens strains

Thirty strains of Butyrivibrio fibrisolvens isolated in diverse geographical locations were examined for esterase activity by using naphthyl esters of acetate, butyrate, caprylate, laurate, and palmitate. All strains possessed some esterase activity, and high levels of activity were observed with strains 49, H17c, S2, AcTF2, and LM8/1B. Esterase activity also was detected in other ruminal bacteria (Bacteroides ruminicola, Selenomonas ruminantium, Ruminobacter amylophilus, and Streptococcus bovis). For all B. fibrisolvens strains tested, naphthyl fatty acid esterase activity paralleled culture growth and was predominantly cell associated. With strains 49, CF4c, and S2, the activity was retained by protoplasts made from whole cells. Esterase activity was detected with all strains when grown on glucose, and some strains showed higher activity levels when grown on other substrates (larchwood xylan or citrus pectin). When nitrophenyl esters of fatty acids were used to measure esterase activity, generally four- to sevenfold-higher activity levels were detected, and with a number of strains substantial levels were found in the culture fluid. Cultures of these strains (H17c, NOR37, D1, and D30g) contained xylanase and acetyl xylan esterase activities, neither of which was associated to any great extent with the cells. Acetyl xylan esterase has not been previously detected in ruminal bacteria and may be important to overall digestion of forage by these organisms.