Isolation and Identification of Toluene-Metabolizing Bacteria from Rhizospheres of Two Indoor Plants

The role of the rhizosphere microbial community in removing volatile organic compounds has not been well investigated. In this study, two species of indoor foliage plants, Fittonia verschaffeltii var. argyroneura and Hoya carnosa, were primed with toluene exposure for 2 months, followed by isolation and identification of the rhizosphere bacteria that were demonstrated to metabolize toluene. A total of 42 bacterial isolates were obtained. The number of bacterial isolates was narrowed down to 23, which had banding pattern similarities of 80 % or less, using BOX-polymerase chain reaction (PCR) fingerprinting technique. The 23 isolates were further characterized by sequencing part of their 16S rDNA after PCR. Their identities were examined using Basic Local Alignment Search Tool (BLAST), resulting in the isolates having the highest sequence similarities (97-100 %) to eight known bacteria strains, none of which had been previously reported to be capable of degrading toluene. The bacterial isolates were positive for toluene monooxygenase gene, confirming their genetic potential to metabolize toluene. Five of the isolates were further tested with C-14-labeled toluene to directly show their ability to metabolize toluene. Isolate type did not significantly affect the percent of toluene mineralized over 2 weeks' time. However, the isolates had differing response to varying toluene concentrations. Under low (0.05) and high (0.2 mu Ci/mL) concentrations, they mineralized 43 and 49 % of toluene, respectively. The isolation and characterization of toluene-metabolizing bacteria corroborates previous speculation that the rhizosphere microbial community contributes to the phytoremediation potential of indoor foliage plants.