The development of an acetic acid-degrading microbial strain that tolerates 4-chloro-2-methylphenoxyacetic acid and 2,4-dichlorophenoxyacetic acid.

Abstract

Anthropogenic organic compounds are extensively utilized in agriculture as pesticides, herbicides, fungicides, and insecticides. For over 30 years, the predominant herbicides utilized globally have been phenoxy acid herbicides, particularly 4-chloro-2-methylphenoxyacetic acid (MCPA) and 2,4-dichlorophenoxyacetic acid (2,4-D). In the present study, microbial strains were isolated from contaminated agricultural soil samples to examine the impact of herbicides on growth and degradation under various parameters and environmental conditions. Five microbial strains were isolated from contaminated soil samples containing herbicides. The bacterial strain Micrococcus luteus LKDA1 demonstrated the ability to utilize MCPA and 2,4-D as carbon sources, achieving complete degradation of these compounds despite a lower cell growth rate. Under optimum conditions, a prolonged lag phase of 4 to 6 h was observed in enriched medium containing herbicides, whereas in minimal medium, cell growth reached maximum absorbance of 0.30 at 600 nm at 30 °C effectively degrading 98% of each herbicide individually after 5 days of incubation. Higher concentrations of 2,4-D have a toxic effect on cell growth; nonetheless, the degradation rate was 99%, suggesting that strain LKDA1 was able to tolerate higher concentrations easily. Micrococcus luteus LKDA1 achieved a 99% degradation rate of MCPA at a maximum concentration of 700 mg/L. Herbicide compounds belong to the same family yet exhibit opposing effects on the cell survival rates, with 2,4-D being damaging and MCPA promoting survival. Micrococcus luteus LKDA1 degrades 2,4-D and MCPA even with a reduced cell population; it can tolerate these compounds and utilize them as a sole carbon source for survival.