Microbial biodegradation of 2,4,5-trichlorophenoxyacetic acid and chlorophenols

We have succeeded in isolating a pure culture of Pseudomonas cepacia, AC1100, from a chemostat enrichment culture experiment that is capable of growing on 2,4,5-trichlorophenoxyacetic acid as its sole source of carbon and energy. AC1100 is not only capable of degrading 2,4,5-T but is also able to completely or partially dehalogenate a wide variety of halophenols. The regulation of the dehalogenating ability of AC1100 has been investigated which demonstrates that the enzyme(s) which allow the conversion of 2,4,5-T to 2,4,5-TCP are constitutive, while the enzymes that allow the degradation of 2,4,5-TCP are inducible by 2,4,5-TCP (or some metabolite of 2,4,5-TCP) but not by 2,4,5-T or other halophenols which can serve as substrates. Moreover, the 2,4,5-TCP degradative pathway is repressed by the presence of an abundant alternative carbon source. The detailed pathway of 2,4,5-T degradation by AC1100 is currently under study. Although field tests have yet to be conducted, laboratory experiments have demonstrated rapid and complete degradation of 2,4,5-T from contaminated soil. Soil previously contaminated with as much as 5,000 micrograms of 2,4,5-T/g of soil could be detoxified by AC1100 treatment, allowing the growth of plants sensitive to less than 10 micrograms 2,4,5-T/g of soil. Moreover soil contaminated with as much as 20,000 micrograms of 2,4,5-T/g of soil showed greater than 90% degradation after six weekly AC1100 treatments. After 2,4,5-T has been substantially degraded in contaminated soil the titer of AC1100 rapidly falls to nearly undetectable levels, which indicates that no serious ecological disturbance is likely to result from the application of AC1100. It appears possible that the treatment of contaminated areas with appropriate microorganisms may allow essentially a total restoration of the original soil condition.