Optimization of dimethoate degradation by Brevundimonas sp MCM B-427 using factorial design:: studies on interactive effects of environmental factors

Microbial cultures were isolated from soil exposed to dimethoate, an organophosphorus insecticide. The isolate that showed maximum degradation of dimethoate was identified as Brevundimonas sp. MCM B-427. The curve relating biomass accumulation and degradation revealed that aeration appeared to enhance growth rather than degradation. For optimization of environmental factors, a 2(4) factorial experimental design was used, wherein four factors namely pH, temperature, inoculum density and aeration condition were varied simultaneously. The interaction between the factors was analyzed using MINITAB package. Degradation of dimethoate was affected by a large number of factors interacting in a complex way. Six two-way and two three-way interactions of various environmental factors were found to be statistically significant. In all the two-way interactions, the effect of one factor was more pronounced when the other was at its optimum. The three-way interactions revealed that optimization of pH, inoculum size and aeration was more critical at 40degreesC than at 30degreesC. The results imply the importance of studying interactions of parameters rather than optimizing individual parameters one by one. These results demonstrate complexity of the interaction and thereby imply the need for better experimental and statistical models.