Exploration of 2, 4-dichlorophenoxyacetic acid degradation by an indigenous Klebsiella pasteurii Ko4: effects of environmental and nutritional factors

The extensive use of the phenoxy herbicide 2, 4-dichlorophenoxyacetic acid (2, 4-D) has led to its persistent accumulation in agricultural environments, posing potential risks to ecosystems and human health. This study aimed to isolate and characterize an indigenous 2, 4-D-degrading bacterium and evaluate its degradation efficiency under different environmental and nutritional conditions. An indigenous bacterial isolate, designated Klebsiella pasteurii strain Ko4, was recovered from pesticide-contaminated agricultural soils in Wonji and Meki, Ethiopia, and identified using morphological, biochemical, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and 16S rRNA gene sequencing analyses. The isolate degraded 96.87% of 350 mg L−1 2, 4-D within 16 days in mineral salt medium under optimized conditions. Degradation was significantly influenced by environmental factors (p < 0.05), with optimal performance at pH 7 and 30 °C, indicating a preference for neutral pH and mesophilic conditions. Growth and degradation were concentration dependent, with maximum bacterial growth observed at 500 mg L−1, whereas higher herbicide concentrations inhibited bacterial activity. Nutrient availability also significantly affected degradation (p < 0.05), with carbon-deficient medium supporting the highest degradation (49.89 ± 9.10%) compared with nitrogen-deficient (28.71 ± 8.07%) and phosphorus-deficient conditions, identifying nitrogen as the principal limiting nutrient. These findings indicate that strain Ko4 can effectively degrade 2, 4-D under the tested laboratory conditions, highlighting its potential for further investigation in the bioremediation of 2, 4-D-contaminated environments. Further studies integrating molecular characterization of degradation pathways and field-scale validation are warranted to support its practical application.