Biodegradation of lindane in soils using a dechlorinase produced by an actinomycetes strain

Abstract

There are many reports indicating that hexachlorocyclohexane (γ-HCH) is present in soil, water, air, plants, agricultural products, animals, food, microbial environments and humans. Considered a potential carcinogen and listed as a priority pollutant by the US EPA, γ-HCH is a lipophilic compound and therefore tends to accumulate and concentrate in the body fats of animals and humans. The γ-HCH is an organochloride pesticide used in agriculture and medicine at the international level. It has a great tendency to bioaccumulate in the environment and humans. In Salí River, Tucumán, Argentina, lindane was detected 10-fold in relation to the permitted trace concentrations. The development of new technologies to remediate these sites using a specific enzyme is now more necessary than ever. The actinomycetes are Gram positive bacteria with great potential to bioremediate soil. Streptomyces sp. M7 was isolated from contaminated sediments with the capacity to grow in the presence of lindane as the only carbon source and to remove it from a culture medium and soil samples. For the first time, in this strain, an enzyme was detected that can dechlorinate lindane; it is called dechlorinase. There are some reports regarding aerobic degradation of γ-HCH by Gramnegative bacteria like Sphingomonas and by the white-rot fungi Trametes hirsutus, Phanerochaete chrysosporium, Cyathus bulleri and Phanerochaete sordida. However, little information is available on the ability of biotransformation of organochlorine pesticides by Gram-positive bacteria and particularly by actinomycete species, the main group of bacteria present in soils and sediments.Since the toxicity of γ-HCH is well established, it is imperative to develop methods by which lindane can be removed from the environment. It was demonstrated that Streptomyces sp. M7 possesses the LinA enzyme that catalyzes dehydrochlorination of γ-HCH to 1,3,4,6-tetrachloro-1,4-cyclohexadiene (1,4-TCDN) via γ-pentachlorocyclohexene (γ-PCCH). The increase of γ-PCCH was detected in time by Gas Chromatography (GC). This strain can be useful in the study of the bioremediation capacity by dechlorinase from Streptomyces sp. M7 in soil contaminated with lindane.