Differences in adsorption, transmembrane transport and degradation of pyrene and benzo[a]pyrene by Bacillus sp. strain M1

In a previous study our group identified Bacillus sp. strain M1 as an efficient decomposer of high molecular weight-polycyclic aromatic hydrocarbons (HMW-PAHs). Interestingly, its removal efficiency for benzo[a]pyrene (BaP) was nearly double that of pyrene (Pyr), which was the reverse of what is reported for most other species. Here we compared the differential steps of biosorption, transmembrane transport and biodegradation of Pyr and BaP by strain M1 in order to assist in targeted selection of dominant strains and their degradation efficiency in the remediation of these two HMW-PAHs. The overall biosorption efficiency for BaP was 19% higher than that for Pyr, and the time needed to reach BaP peak adsorption efficiency was 4 days shorter than for Pyr. Transomembrane transport of the PAHs was compared in presence of sodium azide which inhibits ATP synthesis and metabolism. This indicated that both Pyr and BaP entered the cells by the same means of passive transport. Biodegradation of Pyr and BaP did not differ in the early stage of culture, but around days 5-7, the biodegraodation efficiency of BaP was significantly (30-61%) higher than that of Pyr. Key enzymes involved in these processes were identified and their activity differed, with intracellular gentisate 1,2-dioxygenase and extracelolular polyphenol oxidase as likely candidates to be involved in BaP degradation, while intracellular catechol-1,2dioxygenase and salicylate hydroxylase are more likely involved in Pyr degradation. These results provide new insights for sustainable environmental remediation of pyrene and benzo(a)pyrene by these bacteria.