Abstract
Investigation of the phosphate effect and feeding strategy, i.e. linear and exponential feeding, to improve beta-lactamase production by Bacillus licheniformis considering the viability of the cells. Effect of phosphate enrichment on beta-lactamase production was investigated and resulted in 1.2-fold increase in beta-lactamase activity. Thereafter, exponential and linear feed profiles were established, after an initial batch phase for t = 0-7.5 h. The highest beta-lactamase activity was obtained at fed-batch operation with exponential feeding (FBO1) condition as A = 106 U cm(-3), which is c. 1.7-fold higher than that of the phosphate-enriched batch operation (PE-BO). Biphasic variations in beta-lactamase production was enhanced to monophasic variation with the exponential feeding strategy where the activity was obtained as A = 106 U cm(-3) at t = 16 h. Phosphate enrichment decreases the intracellular ammonium concentration and organic acid excretion, but increrases beta-lactamase production. When batch operation (BO) and PE-BO are compared, it is seen that succinic acid formation decreased with the phosphate enrichment as a result of smooth operation of the tricarboxylic acid cycle. At FBO1 despite the increased lactic and acetic acid formation, beta-lactamase production increased 1.7-fold, and 92% of the cells were alive at the end of the fermentation.
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