Statistical experimental methods for optimizing the cultivating conditions for Rhodococcus erythropolis

Rhodococcus erythropolis was found to effectively degrade aflatoxin B-1 produced by Aspergillus flavus and Aspergillus parasiticus. However, one problem of concern was the slow growth of this strain. In this study, Plackett-Burman design was used to select the most important variables, namely, temperature, pH, inoculum size, liquid volume, agitation speed and culture time that affected the growth of R. erythropolis. Central composite experimental design and response surface analysis were adopted to derive a statistical model for optimizing the culture conditions. From the obtained results, it can be concluded that the optimum parameters were: temperature, 15.3 degrees C; pH, 5.56; inoculum size, 4%; liquid volume, 70 ml in 250 ml flask; agitation speed, 180 rpm; and culture time, 58.2 h. At this optimum point, the populations of the viable organisms could reach 10(8) colony forming units (CFU)/ml, which was 100 times higher than that incubated under the initial conditions. After 58.2 h incubation in this optimum cultivating conditions, 53.9 +/- 2.1% of aflatoxin B-1 was degraded, while only 20.6 +/- 1.4% of aflatoxin B-1 was degraded in the initial conditions.