Growth Kinetics and Inhibition of the Lipolytic Thermophile Bacillus thermoleovorans IHI-91
Peter BECKER*a, Mladen N. POPOVa, Samson MARKOSSIANb, Garabed ANTRANIKIANb and Herbert MfRJKa
a Department of Bioprocess and Biochemical Engineering, Technical University Hamburg - Harburg, Denickestr. 15, 21071 Hamburg, Germany
b Department of Technical Microbiology, Technical University Hamburg - Harburg, Denickestr. 15, 21071 Hamburg, Germany
Detailed fermentation studies have been undertaken in order to elucidate the growth kinetics of the newly isolated lipolytic thermophile Bacillus thermoleovorans IHI-91. It was shown that the maximum specific growth rate at the optimal growth temperature of 65℃, μmax is extremely high with 1.2 h-1 for olive oil and even 2.9 h-1 for yeast extract. Continuous culture studies allowed to use a mathematical model which is based on Monod kinetics and involves maintainance requirements and wall growth of the cells. For olive oil a maintainance coefficient of 0.04 h-1 was measured which is within the range of mesophilic microorganisms. The substrate saturation constants Ks were found to be relatively high which confirms our previous work (1). Furthermore our finding indicate that the yield coefficient for growth on olive oil is in the order of 1 g dry cell mass/g substrate. In carrying out a shift in the feed substrate concentration (s-shift) at a constant dilution rate of 0.3 h-1 we found that olive oil feed concentrations above 4 g/1 caused severe inhibition with detrimental effects on biomass and lipase productivity. Batch and continuous culture studies revealed that growth inhibition occurred when oleic and acid, the primary hydrolysis product of olive oil, exceeded levels of 100-150 mg/1.
1. Becker, P., Abu-Reesh, I., Markossian, S., Antranikian, G., and Markl, H. (1997) Appl. Microbiol. Biotechnol., 48, 184-190.
