Journal of Environmental Science and Health Part B (2009) 44, 663–672 C Taylor & Francis Group, LLC Copyright ISSN: 0360-1234 (Print); 1532-4109 (Online) DOI: 10.1080/03601230903163665
Enrichment and isolation of endosulfan-degrading microorganism from tropical acid soil SURYA KALYANI S1 , JITENDER SHARMA2 , SURENDER SINGH3 , PREM DUREJA4 and LATA3 1
Food and Agriculture Department, Bureau of Indian Standards, New Delhi, India Department of Biotechnology, Kurukshetra University, Kurukshetra, Haryana, India 3 Division of Microbiology, Indian Agricultural Research Institute, New Delhi, India 4 Division of Agricultural Chemicals, Indian Agricultural Research Institute, New Delhi, India Downloaded By: [Consortium for e-Resources in Agriculture] At: 12:13 16 September 2009
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Endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,3,4-benzo-dioxathiepin-3-oxide) is a cyclodiene organochlorine currently used as an insecticide all over the world and its residues are posing a serious environmental threat. This study reports the enrichment and isolation of a microbial culture capable of degrading endosulfan with minimal production of endosulfan sulfate, the toxic metabolite of endosulfan, from tropical acid soil. Enrichment was achieved by using the insecticide as sole sulfur source. The enriched microbial culture, SKL-1, later identified as Pseudomonas aeruginosa, degraded up to 50.25 and 69.77 % of α and β endosulfan, respectively in 20 days. Percentage of bioformation of endosulfan sulfate to total formation was 2.12% by the 20th day of incubation. Degradation of the insecticide was concomitant with bacterial growth reaching up to an optical density of 600 nm (OD600) 2.34 and aryl sulfatase activity of the broth reaching up to 23.93 µg pNP/mL/hr. The results of this study suggest that this novel strain is a valuable source of potent endosulfan–degrading enzymes for use in enzymatic bioremediation. Further, the increase in aryl sulfatase activity of the broth with the increase in degradation of endosulfan suggests the probable involvement of the enzyme in the transformation of endosulfan to its metabolites. Keywords: Biodegradation; endosulfan; endosulfan sulfate; Pseudomonas aeruginosa; tropical acid soil.
Introduction Endosulfan (6, 7, 8, 9, 10, 10-hexachloro-1, 5, 5a, 6, 9ahexahydro-6, 9-methano-2, 3, 4-benzodioxyanthiepin- 3oxide) is widely employed as an insecticide in world agriculture. Technical grade endosulfan contains two stereoisomers, α and β endosulfan in the ratio of 7: 3. In the close vicinities of agricultural fields, the contamination of atmosphere, soils, sediments, surface and rain waters and foodstuffs by endosulfan has been documented in numerous previous studies.[1] The persistence of endosulfan in soil and water environments has been observed by different researchers under different conditions.[2,3] Its harmful impacts on aquatic fauna and numerous mammalian species including human beings have been reported several times in literature.[4−7] Detoxification of pesticides through biological means is receiving serious attention as an alternative to existing methods, such as incineration and landfill. A preliminary Address correspondence to Jitender Sharma, Department of Biotechnology, Kurukshetra University, Kurukshetra, Haryana, India; E-mail: jksharma.kuk@gmail.com Received December 3, 2008.
step in the investigation of enzymatic technologies for endosulfan detoxification is the definitive identification of a biological source of endosulfan–degrading activity. In a bioremediation process, heterotrophic microorganisms break down substrates (hazardous compounds) to obtain chemical energy, hence organic pollutants can serve as carbon, energy and nutrient sources for microbial growth. Some studies have described endosulfan as a sulfur source for microbial growth and a poor biological energy source when used as a sole carbon source.[8,9] Sutherland et al.[8] selected microorganisms for their ability to release the sulfite group from endosulfan and to use this insecticide as a source of sulfur for bacterial growth. Awasthi et al.[10] isolated a bacterial co-culture using endosulfan as a sole carbon source. To date, some physicochemical and biological remedial strategies have been described by researchers which lead to degradation of endosulfan into both toxic and non-toxic metabolites.[8−22] In this study we are reporting a bacterial strain SKL-1, isolated using enrichment with endosulfan as sole sulfur source. The organism identified as Pseudomonas aeruginosa, is the most active endosulfan-degrading single strain of microorganism, with minimal production of endosulfan sulfate, the toxic metabolite of endosulfan degradation.