Utilization of plan terpenes for induction of Rhodococcus pyridinivorans L4 bacteria to degrade trichloroethylene (TCE) and characterization of involving gene

Abstract

Trichloroethylene (TCE) is a priority pollutant that causes widespread contamination of water and soil. Biodegradation of TCE has the potential for being a cost-effective remediation technology. This study focused on the application of a local bacterium, Rhodococcus pyridinivorans L4 that normally cometabolize TCE while growing on toluene. Various plant terpenes were investigated as alternative TCE degrading enzyme inducers. Citral, cumene, and limonene at 25-50 ppm induced the bacterium to degrade 70% of 15 ppm TCE within 30 hrs. Terpene induced cells were also mineralized TCE more than non-induced cells. R. pyridinivorans L4 along with lemon grass leaves, cumin seeds, or orange peels were effectively enhanced TCE degradation in soil microcosms. Characterization of the initial TCE degrading enzyme and its encoding gene were later carried out by enzyme and DNA assay. The results suggested that R. pyridinivorans L4 contained toluene dioxygenase encoding gene, which is also found in other TCE/toluene degrading bacteria. DNA sequences of the gene were 100% homology to toluene inducible dioxygenase large subunit in Rhodococcus sp. 124, an isolate from USA. RT-PCR analysis revealed that terpene induced cells expressed higher amount of dioxygenase gene than non-induced cells. Meanwhile, toluene grown cells contained the highest amount of dioxygenase mRNA.