Optimization of process parameters for biodegradation of malathion by Micrococcus aloeverae MAGK3 using Taguchi methodology and metabolic pathway analysis

Abstract

In this study, a previously isolated bacterial strain, Micrococcus sp. MAGK3 was employed to explore its malathion biodegradation potential. A considerable degradation (66.79%) was attained with malathion (0.03%) being the sole carbon source after 240 h of incubation. To enhance malathion biodegradation, effects of co-substrates, pH, temperature, initial malathion concentration, agitation (rpm), and inoculum size were evaluated using Taguchi methodology. Experiments with various combinations of factors were conducted, and results in respect of malathion biodegradation were evaluated in the Qualitek-4 software to determine the key effect of individual factors, their interaction effects, and optimal levels of process factors. All parameters contributed to malathion biodegradation, and Taguchi DOE's ability to predict optimum response, was established by experimentation via optimized levels of factors (carbon source 0.1%, nitrogen source 0.1%, pH 7, temperature 35 °C, pesticide concentration 0.03%, agitation 150 rpm, and inoculum size 2%(w/v). Results confirmed that pesticide concentration caused the maximum impact (34.09%) on malathion degradation followed by nitrogen source (32.11%), temperature (20.99%), RPM (6.55%), inoculum size (3.26%), carbon source (2.81%) and pH (0.2%). Before optimization, Micrococcus sp. MAGK3 had an average degradation of 57.94% within 168 h, but after optimization, the rate of biodegradation improved to 87% within 38 h. Confirmation of malathion biodegradation was performed by UHPLC, and GC-MS analysis and a possible degradation pathway was proposed for malathion biodegradation by Micrococcus sp. MAGK3. For the time being, this is the first publication to employ the Taguchi design of experiment to optimize the degradation of malathion by Micrococcus sp. MAGK3.