Collection and preparation of soil sample With the help of sterile spatula, approximately 10g soil sample was collected from each of the several sites of different paddy field of Noakhali, Bangladesh that have undergone repeated treatment with chemical pesticides. The soil sample mainly constituted top soil layer. All the samples were then transported to the laboratory for analysis within a short period of time. Selective enrichment for pesticide degrading baceteria For selective enrichment, analytical grade malathion (PESTANAL, Fluka chemical, Sigma) was used as a as a sole source of carbon. Sterilized liquid minimal salt medium (MSM) was used for selective enrichment which contained following ingredients with their concentration in the parentheses: NH4 Cl (0.05%), Na2HPO4 .2H2O (0.64%), KH2PO4 (0.025%), MgSO4 .7H2O (0.02%), NaCl (0.05%). About 250ml sterilized MSM broth was taken in an Erlenmeyer flask and malathion (50mg/l) was added to it as sole source of carbon. A control flask was maintained without the pesticide to compare the pesticide degradation ability of the bacteria. An amount of 2.5g soil sample was measured and added to the pesticide containing enrichment media and the control flask. Both the flasks were incubated at 370C for 7 days. The flasks were observed periodically for change of colour or formation of turbidity due to pesticide degradation. Isolation of pesticide degraders on solid media Sterilized MSM agar media with 2% agar supplemented with malathion (50mg/l) was poured onto sterile petri plates and allowed to solidify. A loopful of enrichment culture from the pesticide supplemented flask was streaked onto the surfaces of the pesticide supplemented solidified MSM agar media. The plates were then incubated at 37oC for 7 days. A control plate containing MSM media without pesticide supplementation was maintained for each of the treated plates. After incubation, both control and treated plates were observed for bacterial growth. The colonies that had grown in pesticide supplemented plates were selected for further investigation. Selected colonies were presumed initially as pesticide degraders and were repeatedly streaked on nutrient agar plates to obtain pure, isolated colonies. The isolates were preserved as stock culture in nutrient agar slants at 4oC. Morphological and cultural studies of the selected isolates The selected isolates were streaked on nutrient agar medium to distinguish their morphological characters such as size, shape (rhizoidal, irregular, circular, undulate, spindle, filamentous, punctiform etc.), edge (curled, lobate, entire, crenate, dentate, filamentation, rhizoidal, etc.) elevation (raised, flat, convex, concave, papillate, umbonate, etc.), opacity, surface (smooth, rough, glistering, crispy etc.) and color of the colony (various shades of color). For the study of size and shapes of the bacterial cells, two types of differential staining techniques, gram staining and endospore staining was performed to observe the shape and arrangement of vegetative cells as well as differentiate the isolates into different broad groups such as Gram positive, Gram negative, spore or non-spore formers.Screening of the isolates based on their growth rate Growth of the different organisms was tested by growing each isolate in a 150 ml conical flask containing 50 ml of the screening medium (MSM) supplemented with 50mg/mlstock solution of malathion. To make sure all the inoculums had same density of bacteria; 1mlinoculum culture in LB broth was taken in a micro-centrifuge tube and centrifuged at 5000 rpm for 10 minutes to separate the cells from the growth medium. The supernatant was poured off and the pellet containing bacterial cells was washed twice with sterilized 0.9N NaCl solution. The cells were then diluted with 0.9N NaCl solution to adjust their optical density (OD) value to 1.0 measured at 600 nm with an UV-Visible spectrophotometer. The ability of each isolate to utilize pesticide was assessed by periodical measurement of turbidity at 600 nm using a UV-Visible spectrophotometer. For each isolate, a control flask was maintained without the addition of any pesticides. The OD600 value of the control was also measured and recorded following aforementioned procedure. To select the most potent degrading strains paired t-test was performed with OD600 values of control and pesticide supplemented flasks using Graph Pad Prism software. The islolates, which showed significant difference (P<0.05) in growth by utilizing malathion compared to control in the growth curve, were selected for further analysis. Growth comparison of the isolates based on temperature. The isolates were assessed for their pesticide degrading capabilities in different temperature schemes. For this experiment, the isolates were inoculated in 50 ml MSM media supplemented with 50 mg/l of malathion and incubated at 25oC, 35oC and 45oC respectively. The inocula were prepared by following the previously mentioned method mentioned in above section. Identification of the isolates based on their morphological and biochemical properties The isolates that showed significant pesticide degrading capabilities were selected for identification based on their morphological and biochemical characteristics. By following Reza et. al. 18 Bergey’s Manual of Systematic Bacteriology the following important physiological and biochemical tests of the isolated bacteria were carried out viz., Gram staining, endospore staining, catalase test, mannitol fermentation, oxidase test, glucose fermentation, fluorescent pigment formation test, methyl red test, voges-proskaur test, h2 s production, citrate utilization test, starch hydrolysis, gelatin hydrolysis, motility test, indole test, and urease test. Statistical analyses All the statistical analyses were done using Graph Pad Prism software. Paired t-test was performed to obtain P-value to determine the significance level (P<0.5) of an experiment when two sets of data were compared. Two-way ANOVA test was performed when a set of grouped data was analyzed to obtain the significance of the results.