Enhanced microbial degradation of benzo(k)fluoranthene by newly isolated Priestia megaterium AVNR4: process optimization and characterization

Benzo(k)fluoranthene (BkF) is a high molecular weight polycyclic aromatic hydrocarbon (HMW PAH) identified as a priority pollutant with major adverse effects on human and animal health and on environment. This work focuses on the isolation, characterization, and optimization of BkF degrading bacteria obtained from hydrocarbon contaminated soils in automobile garages. The bacteria were isolated using the culture enrichment technique with Bushnell-Haas (BH) medium supplemented with BkF as sole carbon source. Five Bacterial isolates were collected and evaluated for their efficacy to degrade BkF. The bacterial isolate AVNR4 was chosen for its ability to degrade BkF with an efficiency above 75%. The morphological and molecular characterization of the bacterial isolate AVNR4 revealed its classification as Priestia megaterium. The capacity of Priestia megaterium AVNR4 to synthesize biosurfactants has been confirmed by Fourier Transform Infrared (FTIR) spectroscopy. The biodegradation efficacy of Priestia megaterium AVNR4 for BkF may be enhanced by optimizing crucial variables such as temperature, pH, salinity, starting BkF concentration, and co-substrate addition using the One-Factor-at-a-Time (OFAT) methodology. The OFAT optimization results revealed the optimal conditions as temperature 35 °C, pH 7.5, salinity 3%, an initial BkF concentration of 600 mg L−1, and a co-substrate concentration of maltose at 1000 mg/L, yielding BkF biodegradation efficiencies of 91.79%, 98.44%, and 100% on the 10th, 20th, and 30th days, respectively. The key intermediate metabolites detected through GC–MS analysis during the biodegradation of BkF by Priestia megaterium AVNR4 comprise 2,4-Di-tert-butylphenol, 7-methoxy-2-methylquinolin-4-ol, 2-formylacenaphthylene-1-carboxylic acid, n-hexadecanoic acid, ascorbic acid dihexadecanoate, pentadecanoic acid, 1-tetradecanol and 1-hexadecanol signifying a hybrid approach involving oxidative and β-oxidative pathways for the mineralization of BkF. Overall, this work underscores the potential of Priestia megaterium AVNR4 as a promising strain for the bioremediation of environments contaminated with a HMW PAHs, namely benzo[k]fluoranthene.