The influence of substrate concentration and growth phase on expression of Butyrivibrio sp. Mz5 endoxylanases
Zorec, M. | Marinsek-Logar, R. | Cepeljnik, T. | Nekrep, F.V. (Ljubljana Univ. (Slovenia). Biotechnical Fac., Zootechnical Dept.)
Butyrivibria represent a significant proportion of bacterial isolates from different ruminants. The strain Butyrivibrio sp. Mz5 was originally isolated from the rumen of a black and white Frisian cow. It possesses very high xylanolytic activity, at least 1.65 times higher than any of the tested anaerobic bacteria, as shown earlier. The inducibility by substrate, the influence of substrate concentration and growth phase on expression of its endoxylanases were tested in the present work. Xylanase activity of Butyrivibrio sp. Mz5 was found to be inducible, the specific activity of cells grown on xylan being increased 34-fold in comparison with cells grown on soluble carbon sources. The 51 kDa- and 145 kDa-endoxylanases are constitutive. The highest xylanolytic activity was detected after 16 hours growth and at 0.5% xylan concentration in growth medium. The majority of the xylanolytic activity was cell bound. Lower concentrations of xylan promoted the release of xylanolytic enzymes into the medium. The 26.7 kDa endoxylanase showed resistence to lower pH. The data obtained will help to achieve maximal xylanolytic activity for the needs of enzyme purification.
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