Characterization of Esterases Produced by a Ruminal Bacterium Identified as Butyrivibrio fibrisolvens

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Abstract
An obligately anaerobic ruminal bacterial isolate was selected from 18 tributyrin-degrading isolates and identified as Butyrivibrio fibrisolvens strain 53. The culture in late exponential phase contained enzymes which could be released by sonic disruption. These enzymes degraded substrates at a rate in the order 1-naphthyl acetate (NA) > 1-naphthyl butyrate > 1-naphthyl propionate but did not degrade 1-naphthyl palmitate or 1-naphthyl phosphate. The enzymes on NA were neither stimulated nor inhibited by CoCl 2 , MgCl 2 , and MnCl (each varied from 10 −6 to 10 −4 M). CaCl at 10 −3 M stimulated esterase activity by 16%. Aliphatic substrates were hydrolyzed at a rate in the order triacetin > tributyrin > tripropionin, and ethyl acetate > ethyl formate. Similarly, aromatic fluorescein diesters were degraded at a rate in the order acetyl > propionyl > caproyl > butyryl > capryl > lauryl. Polyacrylamide gel electrophoretic zymograms indicated that the enzyme composite contained cathodally migrating bands. By column chromatography, these enzymes were separated into six NA-degrading fractions. Fraction V contained an esterase which had an optimal temperature of 39 C, a K m of 7.6 × 10 −4 on NA, and a molecular weight of about 66,000. This enzyme was inhibited by paraoxon (41%, 10 −4 M), eserine (17%, 10 −2 M), NaF (17%, 10 −2 M), and diisopropyl fluorophosphate (62%, 10 −4 M) but not by 1-naphthyl N -methyl carbamate at 8.4 × 10 −4 M.