Biotransformation of pentachlorophenol by Chinese chive and a recombinant derivative of its rhizosphere-competent microorganism, Pseudomonas gladioli M-2196

The use of plants or microorganisms to detoxify contaminated soil or groundwater is a potentially cost-effective alternative to traditional remediation technologies. This study investigated the effects of a rhizosphere microbe on the biotransformation of pentachlorophenol (PCP). Chinese chive (Allium tuberosum Rottler) and its rhizosphere-competent bacterium, Pseudomonas gladioli M-2196, were used as a plant–bacterium pair. The genes encoding PCP-degrading enzymes from Sphingobium chlorophenolicum ATCC39723 were introduced into the chromosome of P. gladioli M-2196. The resultant transformants were able to degrade PCP almost completely in liquid medium within 4 d in culture. PCP degradation experiments showed that the amount of PCP in soil (3.3 μg g−1) planted with the P. gladioli transformant (T-9) and Chinese chive decreased by 40% as compared with untreated soil (control) by day 28. Strain T-9, which was used in the PCP degradation experiments, retained the ability to colonize the Chinese chive rhizosphere after 28 d. Tetrachlorocatechol (TCC) was detected as a metabolite of PCP in Chinese chive extract. The amount of PCP in soil treated only with Chinese chive decreased by 30% as compared with the control, but the total amount of PCP plus TCC detected in the plant was less than 10% of the amount of PCP removed from soil. This might be due to the enhancement of a soil microflora population capable of degrading PCP by root exudates from Chinese chive. Therefore, Chinese chive itself, in addition to the rhizosphere-competent bacterium, seemed to play an important role in reducing the PCP level in the soil.