Researchers have used three bacteria species isolated from domestic sewage to remove chloropyrifos, an organophosphorous pesticide, from water and soil samples. The bacteria absorb the pesticide without leaving behind any toxic metabolites. While the bacteria species, both individually and as mixed culture, removed 90% of the pesticide from water samples, about 50% of the pesticide was removed from soil samples when mixed culture was used.
Using three bacterial species isolated from domestic sewage researchers from India have successfully removed chloropyrifos pesticide from both water and soil samples. Chloropyrifos is an organophosphorous pesticide and is moderately toxic to humans. Poisoning from chlorpyrifos may affect the central nervous system, the cardiovascular system, and the respiratory system.
The highlight of the work is the wholesome removal of the pesticide by the three bacteria species without leaving behind any toxic metabolites which persists in the soil for a long time. This was because, unlike other studies, none of the three bacteria used by the team led by Prof. Mukesh Singh from Haldia Institute of Technology, Haldia degraded the pesticide. The results were published in the journal Bioresource Technology.
“Bacteria found in domestic sewage are quite regularly exposed to low levels of this pesticide. So the bacteria adapt themselves to pesticide exposure for survival. This is the reason why we turned to domestic sewage to isolate the bacteria,” says Prof. Singh. The three bacteria are Pseudomonas aeruginosa, Enterobactor ludwigii and Enterobacter cloacae.
To isolate the bacteria that can absorb the pesticide, the researchers exposed the bacteria found in sewage to different concentration of pesticide along with nutrient media. The next day, seven bacteria that showed tolerance to 50 mg/ml of pesticide were isolated.
The next step was to check if isolated bacteria species could coexist or showed antagonism with each other. Only three bacteria species were found to coexist without any antagonism.
The ability of the bacteria to remove the pesticide was then tested by using very high concentration of 500 mg/l of the pesticide. In the case of pesticide added to water, all the three bacteria both individually as well in a mixed culture were able to remove over 90% of the pesticide in three days.
In the case of soil containing 300 mg/kg of pesticide, the mixed culture of bacteria could remove up to 50% in 30 days. “The mixed culture comprising all three bacteria showed better uptake of pesticide compared with individual species,” says Prof. Singh.
Studies were carried out to confirm the accumulation of the pesticide inside the bacteria and to know where it was found. “The pesticide bioaccumulates in the cell as well as bound on the cell surface without any degradation,” says Md. Shabbier from Haldia Institute of Technology and first author of the paper.
The greater ability of the bacteria to absorb the pesticide arises from their ability to reduce the hydrophobic nature of the pesticide through the production of biosurfactants.
“Since the bacteria multiply in the soil and water, the pesticide released from the dead microbes will be absorbed by the newly formed ones. So it is quite possible that the soil or water will be free of the pesticide,” says Shabbier.
The three bacteria and the mixed culture in soil containing did not inhibit the germination and growth of mung bean seedlings. While samples containing the pesticide destroyed red blood cells of goat blood, the samples treated with the bacteria did not cause any damage to red blood cells. “This once again confirmed that the bacteria had completely removed the pesticide from the samples,” Prof. Singh says.