Oranochlorine pesticides biodegradation by actinomycetes

BENIMELI C.S.; AMOROSO M.J.

Jena, Alemania

Simposio; 5th Symposium on remediation in Jena: “Bio-Geo- Interactions and reactive transport”; 2006

Friedrich-Schiller-University Jena. Institute of Earth Sciences

Pesticides have been extensively used to protect and improve quality and quantity of food commodities, building materials, clothing, animal health, and to combat certain diseases transmitted by insect vectors to man and animals. However, indiscriminate use of pesticides has caused serious concern about toxic effects by residues on non-target organisms. As a consequence and because of their environmental problems and health hazards: aldrin, chlordane, dalapon, DDT, dieldrin, endosulfan, and lindane have been restricted or banned. Because of extensive aldrin, chlordane, and lindane use in the northwest of Argentina, residues are present in the main hydrographic system of Tucumán. Pesticide residues in soils and their subsequent movements in the water–soil systems are key aspects in their environmental behavior. Consequently, reliable, cost effective method(s) for remediation of OP(s) is needed in order to minimize contaminated sites. Metabolic pathways for pesticide biodegradation by Gram negative bacteria have been more extensively studied than in Gram positive bacteria. Additionally, little information has been reported about the ability of OP(s) biotransformation by actinomycete species. Strains belonging to actinomycetes have been able to oxidize and/or partially dechlorinate pesticides. Ninety-three wild-type actinomycetes were tested against 11 OPs: aldrin, chlordane, DDD, DDE, DDT, dieldrin, heptachlor, and heptachlor epoxides, lindane, and methoxychlor. Qualitative screening agar assays displayed 62–78% tolerance of strains to OPs. Four strains designed M4, M7, M9 and M15 were selected based on multi-OP tolerance, and identified as members of the streptomycetes group. Different growth profiles were observed in cultures of the four selected streptomycetes cultured in synthetic medium containing 5–50 mgL-1 aldrin or chlordane or lindane. Increase of aldrin removal by the selected microorganisms was concomitant with the 4.8–36.0 µgL-1 pesticide concentration range. After 72 h of streptomycete M7 growth in synthetic medium containing 48.0 µgL-1 aldrin, the remaining OP concentration in the supernatant was approximately 10% of the initial concentration. Also, in stationary growth phase less than 2.5 µgL-1 aldrin residual concentration was detected in the medium. Later the four previously selected streptomycetes were tested because their capacity to grow in presence of 10 µgL-1 lindane. The best strain was identified as Streptomyces sp. M7 because its capacity to use lindane as the only carbon source. After 96 h of incubation in synthetic medium containing lindane and glucose, a cometabolism with glucose as the main substrate and the pesticide as the secondary substrate could be shown; glucose 6.0 gL-1 improved lindane degradation and obtained biomass. When Streptomyces sp. M7 was cultured in presence of lindane plus glucose, the disappearance of the pesticide from the medium and the lindane degradation was observed after 72 h of incubation, without intracellular accumulation. The effect of low glucose concentration and the addition of lindane at different growing time on the pesticide detoxification ability of Streptomyces M7 were studied. After 96 h of incubation in synthetic medium containing glucose 0.6 g µgL-1with the addition of lindane 100 mg L-1 at 20 h of incubation, a typical diauxic curve was obtained: glucose was the preferred substrate until 24 h, at 48 h, when the carbohydrate was depleted; the microorganism consumed the pesticide like carbon source. On the other hand, lindane removal induction was observed, which was greater when the pesticide was added to the medium at 20 h than 6 h of incubation. Between 72 and 96 h, a maximum of ~86% of the Cl- was released when lindane was added to the medium at 20 h, whereas ~70% and 67% Cl- was released in the medium when the pesticide was added at 0 and 6 h of incubation respectively.