Extensive use of carbofuran insecticide harms the environment and human health. Carbofuran is an endocrine disruptor and has the highest acute toxicity to humans than all groups of carbamate pesticides used. Carbofuran is highly mobile in soil and soluble in water with a lengthy half-life (50 days). Therefore, it has the potential to contaminate groundwater and nearby water bodies after rainfall events. A bacterial strain BRC05 was isolated from agricultural soil characterized and presumptively identified as Enterobacter sp. The strain was immobilized using gellan gum as an entrapment material. The effect of different heavy metals and the ability of the immobilized cells to degrade carbofuran were compared with their free cell counterparts. The results showed a significant increase in the degradation of carbofuran by immobilized cells compared with freely suspended cells. Carbofuran was completely degraded within 9 h by immobilized cells at 50 mg/L, while it took 12 h for free cells to degrade carbofuran at the same concentration. Besides, the immobilized cells completely degraded carbofuran within 38 h at 100 mg/L. On the other hand, free cells degraded the compound in 68 h. The viability of the freely suspended cell and degradation efficiency was inhibited at a concentration greater than 100 mg/L. Whereas, the immobilized cells almost completely degraded carbofuran at 100 mg/L. At 250 mg/L concentration, the rate of degradation decreased significantly in free cells. The immobilized cells could also be reused for about nine cycles without losing their degradation activity. Hence, the gellan gum-immobilized cells of Enterobacter sp. could be potentially used in the bioremediation of carbofuran in contaminated soil.

The effect of heavy metals on the degradation of carbofuran by immobilzed bacterial cell was checked by culturing in the MSM medium at 37oC in the presence of 0-1 mg/L of heavy metals. Bioremediation systems represent a biologically sustainable means to degrading organic pollutants such as carbofuran insecticide, with little energy demand and operational expenses in addition to high efficiency and substrate specificity. Nonetheless, heavy metals present in the agricultural lands may thwart the process efficiency by poisoning carbofuran-degrading microbial isolates. Here, we experimentally tested the tolerance of carbofuran-degrading immobilized bacterial isolated from vegetable plantation area for mercury (Hg) and copper (Cu). The of the tested metals inhibited carbofuran biodegradation to different extents, depending on concentration. At pH of 7.0 and 37°C, complete inhibition of carbofuran biodegradation by Hg occurred 0.4, 0.5, 0.6 and 0.7 mg/L, respectively. Lower concentrations of these metals decreased the rate of carbofuran− biodegradation, with relatively long lag times. Interestingly, the immobilize isolate tolerated higher concentrations, although both the rate and extent of carbofuran− biodegradation were affected.