Determination of the kinetic parameters during continuous cultivation of the lipase-producing thermophile Bacillus sp. IHI-91 on olive oil

Abstract

A thermostable lipase was produced in continuous cultivation of a newly isolated thermophilic Bacillus sp. strain IHI-91 growing optimally at 65 degrees C. Lipase activity decreased with increasing dilution rate while lipase productivity showed a maximum of 340 U l-1 h-1 at a condition rate of 0.4 h-1. Lipase productivity was increased by 50% compared to data from batch fermentations. Up to 70% of the total lipase activity measured was associated to cells and by-products or residual substrate. Kinetic and stoichiometric parameters for the utilisation of olive oil were determined. The maximal biomass output method led to a saturation constant Ks of 0.88 g/l. Both batch growth data and a washout experiment yielded a maximal specific growth rate, mu max, of 1.0 h-1. Oxygen uptake rates of up to 2.9 g l-1 h-1 were calculated and the yield coefficient, Y X/O, was determined to be 0.29 g dry cell weight/g O2. From an overall material balance the yield coefficient, Y X/S, was estimated to be 0.60 g dry cell weight/g olive oil.