Characterisation of the multi-enzyme complex xylanase activity from Bacillus licheniformis SVD1

In previous work, we reported on the identification and purification of a multi-enzyme complex (MEC) from Bacillus licheniformis SVD1. The predominant activity within the MEC was xylanase activity and this study examined the effect of various environmental parameters such as pH, temperature, substrate concentration and compounds such as Mg2+, Mn2+, Fe2+, Zn2+, Ca2+, EDTA, SDS, xylose, xylobiose and ethanol on complexed xylanase activity. The pH optimum was found to be between pH 6.0 and 7.0 and the temperature optimum at 55 °C. High levels of residual activity were present over a broad range of pH values. Enhancement of complexed xylanase activity was found in the presence of Mg2+ at 2 mM and 10 mM, while Ca2+ displayed a slight activation at 2 mM but inhibition at 10 mM. Mn2+, Fe2+, Zn2+, EDTA and SDS all displayed an inhibitory effect on complexed xylanase activity, with the greatest inhibition found in the presence of Mn2+. Xylose and xylobiose were found to enhance complexed xylanase activity up to 50%, which has not been reported in literature previously. Ethanol was found to inhibit complexed xylanase activity in a competitive manner, but 58% residual activity was still present at concentrations of 50 g/l ethanol. Complexed xylanases from B. licheniformis SVD1, being uninhibited by products of degradation and only mildly inhibited by ethanol, would be suitable for use in biotechnological applications such as bioethanol production.