Plant Growth Promoting Bacteria Enterobacter asburiae JAS5 and Enterobacter cloacae JAS7 in Mineralization of Endosulfan

Abstract

Endosulfan and their metabolites can be detected in soils with a history of endosulfan application. Microbial degradation offers an effective approach to remove toxicants, and in this study, Enterobacter asburiae JAS5 and Enterobacter cloacae JAS7 were isolated through enrichment technique. The biodegradation of endosulfan and its metabolites rate constant (k) and DT₅₀ were determined through first-order kinetic models. E. asburiae JAS5 degraded the endosulfan, and its metabolites in liquid medium was characterized by the k which was 0.382 day⁻¹ (α-endosulfan), 0.284 day⁻¹ (β-endosulfan) and 0.228 day⁻¹ (endosulfan sulphate), and DT₅₀ was 1.8 day (α-endosulfan), 2.4 days (β-endosulfan) and 3.0 days (endosulfan sulphate). The α-endosulfan, β-endosulfan and endosulfan sulphate metabolites were present in the liquid medium that was degraded by E. cloacae JAS7 which was characterized by the k of 0.391, 0.297 day⁻¹ and 0.273 day⁻¹, and DT₅₀ was 1.7, 2.3 and 2.5 days, respectively. The infrared spectrum of endosulfan degraded sample in the aqueous medium by E. asburiae JAS5 and E. cloacae JAS7 showed a band at 1402 cm⁻¹ which is the characteristics of COOH group. E. asburiae JAS5 and E. cloacae JAS7 strains also showed the ability of plant growth promoting traits such as indole-3-acetic acid (IAA) production, organic acids production and solubilization of various inorganic phosphates. E. asburiae JAS5 solubilized 324 ± 2 μg ml⁻¹ of tricalcium phosphate, 296 ± 6 μg ml⁻¹ of dicalcium phosphate and 248 ± 5 μg ml⁻¹ of zinc phosphate, whereas E. cloacae JAS7 solubilized 338 ± 5, 306 ± 4 and 268 ± 3 μg ml⁻¹ of tricalcium phosphate, dicalcium phosphate and zinc phosphate, respectively. The IAA production by JAS5 and JAS7 strains were estimated to be 38.6 ± 0.3 and 46.6 ± 0.5 μg ml⁻¹, respectively. These bacterial strains form a potential candidate for bioremediation of pesticide-contaminated agricultural fields. In addition, it has been demonstrated that the development of powder formulation has several advantages including high cell count, longer shelf life, greater protection against environmental stresses and increased field efficacy.