Statistical modeling and optimization of culture conditions by response surface methodology for 2,4- and 2,6-dinitrotoluene biodegradation using Rhodococcus pyridinivorans NT2

To improve biodegradability (% biodegradation) and specific growth rate of Rhodococcus pyridinivorans NT2, culture medium and environmental parameters were screened and optimized using the statistical design techniques of Plackett-Burman and response surface methodology. Of the process variables screened, DNTs (2,4-DNT and 2,6-DNT), MgSO4·7H2O, temperature and inoculum size (O.D.) were selected as the most important (P value <0.05) factors. In multiresponse analysis of central composite design, medium formulation consisting of 474/470 mg l-1 2,4-DNT/2,6-DNT, 0.11 g l-1 MgSO4·7H2O, 37.5 °C temperature and 1.05 OD inoculum size were found to predict maximum % degradation and specific growth rate of 97.55 % and 0.19 h-1, respectively. The validity of the optimized variables was verified in shake flasks. The optimized media significantly shortened the time required for biodegradation of DNTs while providing a nearly 30 % (for 2,4-DNT) and 70 % (for 2,6-DNT) increased biodegradation along with 5.64-fold increase in specific growth rate for both DNTs.