Transgenic Arabidopsis thaliana plants expressing bacterial γ-hexachlorocyclohexane dehydrochlorinase LinA.

BACKGROUND: γ-Hexachlorocyclohexane (γ-HCH), an organochlorine insecticide of anthropogenic origin, is a persistent organic pollutant (POP) that causes environmental pollution concerns worldwide. Although many γ-HCH-degrading bacterial strains are available, inoculating them directly into γ-HCH-contaminated soil is ineffective because of the low survival rate of the exogenous bacteria. Another strategy for the bioremediation of γ-HCH involves the use of transgenic plants expressing bacterial enzyme for γ-HCH degradation through phytoremediation. RESULTS: We generated transgenic Arabidopsis thaliana expressing γ-HCH dehydrochlroninase LinA from bacterium Sphingobium japonicum strain UT26. Among the transgenic Arabidopsis T2 lines, we obtained one line (A5) that expressed and accumulated LinA well. The A5-derived T3 plants showed higher tolerance to γ-HCH than the non-transformant control plants, indicating that γ-HCH is toxic for Arabidopsis thaliana and that this effect is relieved by LinA expression. The crude extract of the A5 plants showed γ-HCH degradation activity, and metabolites of γ-HCH produced by the LinA reaction were detected in the assay solution, indicating that the A5 plants accumulated the active LinA protein. In some A5 lines, the whole plant absorbed and degraded more than 99% of γ-HCH (10 ppm) in the liquid medium within 36 h. CONCLUSION: The transgenic Arabidopsis expressing active LinA absorbed and degraded γ-HCH in the liquid medium, indicating the high potential of LinA-expressing transgenic plants for the phytoremediation of environmental γ-HCH. This study marks a crucial step toward the practical use of transgenic plants for the phytoremediation of POPs.

Degradation of DDT by γ-hexachlorocyclohexane dehydrochlorinase LinA.

1,1,1-Trichloro-2,2-bis(4-chlorophenyl)-ethane (DDT) is the first synthetic insecticide and one of the most widely used pesticides. The use of DDT has been banned, but it remains one of the most notorious environmental pollutants around the world. In this study, we found that γ-hexachlorocyclohexane (γ-HCH) dehydrochlorinase LinA from a γ-HCH-degrading bacterium, Sphingobium japonicum UT26, converts DDT to 1,1-dichloro-2,2-bis(4-chlorophenyl)-ethylene (DDE). Because of the weak DDT degradation activity of LinA, we could not detect such activity in UT26 cells expressing LinA constitutively. However, the linA-deletion mutant of UT26 harboring a plasmid for the expression of LinA, in which LinA was expressed at a higher level than UT26, showed the DDT degradation activity. This outcome highlights the potential for constructing DDT-degrading sphingomonad cells through elevated LinA expression.

A microbial consortium led by a novel Pseudomonas species enables degradation of carbon tetrachloride under aerobic conditions.

Carbon tetrachloride (CT) is a recalcitrant and high priority pollutant known for its toxicity, environmental prevalence, and inhibitory activities. Although much is known about anaerobic CT biodegradation, microbial degradation of CT under aerobic conditions has not yet been reported. This study reports for the first time the enrichment of a stable aerobic CT-degrading bacterial consortium, from a CT-contaminated groundwater sample, capable of co-metabolically degrading 30 µM of CT within a week. A Pseudomonas strain (designated as Stari2) that is the predominant bacterium in this consortium was isolated, and further characterization showed that this bacterium can tolerate and co-metabolically degrade up to 5 mM of CT under aerobic conditions in the presence of different carbon/energy sources. The CT biodegradation profiles of strain Stari2 and the consortium were found to be identical, while no significant positive correlation between strain Stari2 and other bacteria was observed in the consortium during the period of higher CT biodegradation. These results confirmed that the isolated Pseudomonas strain Stari2 is the key player in the consortium catalyzing the biodegradation of CT. No chloroform (CF) or other chlorinated compound was detected during the cometabolism of CT. The whole genome sequencing of strain Stari2 showed that it is a novel Pseudomonas species. The findings demonstrated that biodegradation of CT under aerobic conditions is feasible, and the isolated CT-degrader Pseudomonas sp. strain Stari2 has a great potential for in-situ bioremediation of CT-contaminated environments.