Bacillus spp. isolated from soil in Lebanon can simultaneously degrade methomyl in contaminated soils and enhance plant growth

Abstract

The extensive use of methomyl as a pesticide contributed to its pervasive existence as a pollutant of soil and water resources. In this study, bacteria were isolated from polluted agricultural soils and identified as Bacillus paramycoides and Bacillus proteolyticus. Their methomyl biodegradation efficiencies were evaluated under various experimental conditions in vitro. Bacterial growth was optimized in terms of methomyl concentrations, resulting in maximum growth at 100 mg/L. A considerable degradation was achieved with methomyl being the sole carbon source. Under these conditions, Bacillus spp. degraded 60.6%–62.9% of methomyl in liquid medium when cultured separately, compared to 74.3% degradation when cultured as a consortium within 48 h. Moreover, methomyl bioremediation of artificially contaminated soil varied between 88.3% and 93.2% depending on the used bacterium and soil sterilization status. Furthermore, cell-free extracts of both isolates were tested to inspect their methomyl-degradation activities. The enzymes implicated in such action were mainly located extracellularly, with a lower quota of enzymes available in the intracellular and periplasmic extract. The tested Bacillus spp. also demonstrated considerable corn growth enhancing traits in terms of germination percentages, shoot and root lengths and weights, which were adversely affected by methomyl application. These results illustrate the beneficial use of Bacillus spp. as promising candidates in the bioremediation of methomyl-contaminated sites in conjunction with their contribution as biofertilizers.