A Single Monooxygenase, Ese, Is Involved in the Metabolism of the Organochlorides Endosulfan and Endosulfate in an Arthrobacter sp

Abstract

In this paper we describe isolation of a bacterium capable of degrading both isomers of the organochloride insecticide endosulfan and its toxic metabolite, endosulfate. The bacterium was isolated from a soil microbial population that was enriched with continuous pressure to use endosulfate as the sole source of sulfur. Analysis of the 16S rRNA sequence of the bacterium indicated that it was an Arthrobacter species. The organochloridedegrading activity was not observed in the presence of sodium sulfite as an alternative sulfur source, suggesting that the activity was part of the sulfur starvation response of the strain. A gene, ese, encoding an enzyme capable of degrading both isomers of endosulfan and endosulfate was isolated from this bacterium. The enzyme belongs to the two-component flavin-dependent monooxygenase family whose members require reduced flavin for activity. Nuclear magnetic resonance analyses identified the metabolite of endosulfan as endosulfan monoalcohol and the metabolite of endosulfate as endosulfan hemisulfate. The ese gene was located in a cluster of 10 open reading frames encoding proteins with low levels of sulfur-containing amino acids. These open reading frames were organized into two apparent divergently orientated operons and a gene encoding a putative LysR-type transcriptional regulator. The operon not containing ese did contain a homologue whose product exhibited 62% amino acid identity to the ese-encoded protein.The organochloride (OC) insecticide endosulfan ( Fig. 1) was first released for commercial use in 1954 (19). A relatively reactive sulfur moiety in this compound results in a half-life that is shorter than those of other OCs, and because of this endosulfan is the only OC insecticide registered for use in many countries. Compared to other available insecticides, such as the synthetic pyrethroids, endosulfan has low toxicity for many beneficial insects, mites, and spiders (12). It is therefore important in the management of pest species. However, endosulfan is extremely toxic to fish and aquatic invertebrates, and this has led to an interest in postapplication detoxification of this insecticide (27)(28)(29)(30).Commercial endosulfan is a mixture of two diastereoisomers (approximately 30% ␤-endosulfan and 70% ␣-endosulfan) which differ dramatically in their physicochemical and environmental properties (31). The environmental dispersion pathways include hydrolysis of the sulfur moiety to nontoxic endosulfan diol or oxidation to endosulfate. Endosulfate is more persistent than and as toxic as the parent isomers and thus poses a significant environmental problem (12).Our laboratory is interested in isolating and characterizing bacteria and genes involved in detoxification of OC insecticides, particularly endosulfan and endosulfate, for the development of bioremediation technologies. We recently described Esd, an enzyme from a soil Mycobacterium species that degraded ␤-endosulfan (27,29,30). Esd is a member of the two-component flavin-dependent monooxygenase (TC-FDM) family of en...

Esterase-based metabolic resistance to insecticides in heliothine and spodopteran pests

“…Redox reactions are known in bacteria that can degrade and detoxify endosulfan but to the best of our knowledge, no hydrolytic mechanism for degrading this insecticide has been characterised in any organism to date. 75,76) Nor is it obvious at this point how endosulfan could bind to and be sequestered by an overexpressed esterase, although we have found at least one other report of competitive inhibition of heliothine esterases by another organochlorine (in that case, DDT). 22) Interestingly, there is evidence that esterase-mediated SP resistance in H. armigera leads to negative cross-resistance to the oxadiazine indoxacarb.…”

Biodegradation and bioremediation of pesticide in soil: concept, method and recent developments

“…Esd did not degrade either α-endosulfan or the metabolites of endosulfan and endosulfan sulphate. Wier et al [24] have reported the gene Ese encoding enzyme from monooxygenase family capable of degrading both endosulfan α and β from Arthrobacter sp. After, understanding the gene of interest and enzyme involved, the Superbugs can be created to achieve the desired result at fast rate in short time frame.…”

The enzymatic basis for pesticide bioremediation

“…The sulphur-containing intermediate of endosulfate metabolism has been identifi ed as endosulfan hemisulfate (Fig. 2) [14]. The equivalent metabolite for endosulfan metabolism, endosulfan hemisulfi te, was not detected and likely undergoes rapid desulfurisation to form endosulfan monoalcohol.…”