Biodegradation of dibutyl phthalate and diethyl phthalate by indigenous isolate Bacillus sp. MY156: Characterization, stoichiometry, enzyme activity, and physiological response to cell surface

An indigenous bacterial strain, Bacillus sp. MY156, was isolated from a local wastewater treatment plant and utilized for degradation of dibutyl phthalate (DBP) and diethyl phthalate (DEP). The isolate showed a substrate preference of DBP to DEP. The optimal biodegradation conditions were pH 7, 30 °C, 0.2 (in terms of OD600) inoculum size, and 2 % (v v−1) bacterial load. The biodegradation of DBP and DEP as sole carbon source was comprehensively investigated via degradation kinetics and mass balance analysis. The isolate achieved complete degradation and over 80 % removal of 300 mg L−1 DBP within 60 h and 200 mg L−1 DEP in 5 days. The biodegradation of DBP and DEP fitted the inhibitory kinetic model, and the maximum degradation rates for DBP and DEP were 183.34 and 66.90 mg L−1 day−1, respectively. The cell surface responses to biodegradation were investigated by analyses of morphology, Fourier transform-infrared, and extracellular polymeric substance. The potential intermediates were mono-n-butyl phthalate, mono-ethyl phthalate, phthalic acid, and protocatechuic acid by β-oxidation, hydrolysis, and decarboxylation. The esterase and dehydrogenase activities reached the highest at the initial and middle phases during biodegradation. The docking studies also elucidated the relevant enzyme preferred DBP to DEP via binding energy and bond distance.