Optimization of fermentation condition for antibiotic production by Xenorhabdus nematophila with response surface methodology

Aims: To evaluate the influence of environmental parameters on the production of antibiotics (xenocoumacins and nematophin) by Xenorhabdus nematophila and enhance the antibiotic activity. Methods and Results: Response surface methodology (RSM) was employed to study the effects of five parameters (the initial pH, medium volume in flask, rotary speed, temperature and inoculation volume) on the production of antibiotics in flask cultures by X. nematophila YL001. A 2(5-1)-factorial central composite design was chosen to explain the combined effects of the five parameters and to design a minimum number of experiments. The experimental results and software-predicted values of production of antibiotics were comparable. The statistical analysis of the results showed that, in the range studied, medium volume in flask, rotary speed, temperature and inoculation volume had a significant effect (P < 0.05) on the production of antibiotics at their individual level, medium volume in flask and rotary speed showed a significant influence at interactive level and were most significant at individual level. The maximum antibiotic activity was achieved at the initial pH 7.64, medium volume in 250 ml flask 25 ml, rotary speed of 220 rev min(-1), temperature 27.8 degrees C and inoculation volume of 15.0%. Maximum antibiotic activity of 331.7 U ml(-1) was achieved under the optimized condition. Significance and Impact of the Study: As far as known, there are no reports of production of antibiotic from X. nematophila by engineering the condition of fermentation using RSM. The results strongly support the use of RSM for fermentation condition optimization. The optimization of the environmental parameters resulted not only in a 43.4% higher antibiotic activity than unoptimized conditions but also in a reduced amount of the experiments. The chosen method of optimization of fermentation condition was efficient, relatively simple and time and material saving. This study should contribute towards improving the antibiotics activity of X. nematophila. Integrated into a broader study of the impact of environmental factors on the production of antibiotic, this work should help to build more rational control strategy, possibly involving scale-up of production of antibiotics by X. nematophila.