Optimization of an inducible, chromosomally encoded benzo [a] pyrene (BaP) degradation pathway in Bacillus subtilis BMT4i (MTCC 9447)

Abstract

Benzo [a] pyrene (BaP), a pentacyclic polyaromatic hydrocarbon, is 1 of the 12 target compounds defined in the new US Environmental Protection Agency strategy for controlling persistent, bioaccumulative, and toxic pollutants. We previously isolated a novel strain Bacillus subtilis BMT4i capable of utilizing BaP as sole source of carbon and energy. The present study investigated (1) whether the BaP degradation pathway is inducible, and (2) whether it is plasmid-encoded. Furthermore, physical (temperature, pH, and UV-induced photolysis of BaP) and chemical (BaP concentration, surfactant, and ionic strength) parameters for BaP degradation were determined. Our findings revealed a ten-fold enhanced degradation rate in induced vs non-induced culture in the presence of chloramphenicol, suggesting that the BaP degradation pathway is inducible. Physical methods demonstrated the lack of plasmid in BMT4i—a result further complimented by plasmid curing, which had no effect on BaP degradability thus a chromosomal localization can be inferred. Maximum BaP degradation in BMT4i was observed under the following physical and chemical conditions: 30°C, pH 8.0, UV-induced photolysis of BaP-basal salt mineral medium (BSM), 150 μg/ml BaP, 0.01% Tween-20, and 400–1,800 μM MgSO4. These conditions could be beneficial in the development and standardization of effective bioremediation protocols using B. subtilis BMT4i.