The influence of substrate concentration and growth phase on expression of Butyrivibrio sp. Mz5 endoxylanases | Vpliv koncentracije substrata in faze rasti na izražanje endoksilanaz pri Butyrivibrio sp. Mz5

anglais. 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.

slovène. Butirivibriji so med najpogosteje izoliranimi bakterijami iz vampa različnih prežvekovalcev. Sev Butyrivibrio sp. Mz5 je bil prvotno izoliran iz vampa črno-bele frizijske krave in ima zelo močno izraženo ksilanolitično aktivnost, vsaj 1,65-krat višjo kot ostale preskušane bakterije, kar dokazujejo predhodne raziskave. V tem delu smo preskušali inducibilnost ksilanaz s substratom ter vpliv koncentracije substrata in faze rasti na izražanje ksilanaz tega seva. Dokazali smo inducibilnost ksilanaz Butyrivibrio sp. Mz5, pri čemer je bila aktivnost celic, gojenih na ksilanu, 34-krat večja od celic, gojenih na topnih ogljikovih virih. 51 kDa- in 145 kDa-endoksilanazi sta konstitutivni. Največjo ksilanolitično aktivnost smo določili po 16 urah rasti in pri 0,5% koncentraciji ksilana v gojišču.Večina ksilanaz je bila celično vezana. Nižje koncentracije ksilana v gojišču so pospešile sproščanje ksilanolitičnih encimov v gojišče. 26,7 kDa-endoksilanaza je bila odporna proti nizki pH vrednosti. Pridobljeni podatki bodo pomagali pri izražanju največje ksilanolitične aktivnosti za potrebe izolacije encimov.