DEVELOPMENT OF DEFINED MICROBIAL CONSORTIUM FOR BIOREMEDIATION OF SYNTHETIC PESTICIDE CONTAMINATED SOIL AND WATER

Abstract

Lindane Hexachlorocyclohexane) is detected in the environment even after three decades of its cessation of use. It is also found in milk, blood and food samples indicating the vastness of biomagnification. Organophosphates and pyrethroids are the other classes of pesticides being used frequently nowadays leading to further risk enhancement. Commercial formulations of various pesticides of different classes find direct applications in agriculture. Farmers are encouraged to apply these pesticides to improve the crop production. We tried to study the effects of a few commercially available pesticides on the crop seed germination. Green gram (dicotyledonous crop) and wheat (monocotyledonous crop) seeds were considered for the study. Commercially available pesticides were mixed and spiked into the sterilised soil at various concentrations. Malathion is commercially formulated synthetic pesticide which belongs to organophosphates class. Nowadays it is widely used as an effective insecticide in agriculture, health projects and industries. This study evaluated the effect of different concentrations (2ppm to 400ppm) of Malathion towards seed germination, growth of seedling and various photosynthetic pigments in Vigna radiata L. Two different methods were used, moist sterile filter paper method and soil in cups. Qualitative and quantitative estimation of photosynthetic pigments was performed by using thin layer chromatography and spectrophotometeric methods. The percentage germination as well as growth of seedling in terms of shoots and roots length enhanced at lower concentrations as compared to control on filter paper method, while in soil method morphogenic response significantly declined. A few seedlings turned yellowish green at higher levels (400 ppm) of Malathion but were still viable. Photosynthetic pigments significantly reduced with increasing concentrations of Malathion as compared to control. Microbial degradation is the cost effective and safe strategy that can be developed and adapted for improving the environmental health by remediating lindane contamination. We enriched a bacterial population consisting of morphologically 47 distinct bacteria using commercial formulations of organophosphates and pyrethroids mixture. This consortium showed 55.6% - 90.45 % degradation of 5-30ppm lindane by 6 days. The temperature and pH optima were found to be 30 oC and 6 respectively. When this consortium was induced with lindane in broth only four vi

cultures survived while 24 isolates showed the ability to clear lindane film on a nutrient agar plate. This is the first report with a microbial population enriched completely on mixtures of commercial formulations of organophosphate and pyrethroid classes of pesticides and used for degrading a pure isomer of an organochlorine pesticide i.e. lindane. The strain LR4 exhibited 50% degradation of 20 ppm lindane by 6 days, while the combination studies showed that (LR2 + LR3 + LR4) combination was the most efficient and degraded 25% of the supplied 20 ppm lindane by 6 days. Studies with different carbon compounds resulted in the degradation of 80%, 50%, 45%, and 80% lindane when incubated in presence of glucose (by LR4), peptone (by LR3), Tween 80 (by LR4), and Triton X-100 (by LR4) respectively in 5 days. Degradation model was generated using RSM. The analysis of variance (ANOVA) was determined the factors A, B, C, D, E and interaction of AB, AC, AD, BC, BD, BE, DE have significant effect (p<0.0001) on lindane degradation. 16S rDNA analysis revealed the identities of the four strains as LR1- Bacillus cereus; LR2- Pseudomonas sp; LR3- Chryseobacterium sp; and LR4- Pseudomonas putida.