Statistical optimization and ecotoxicological assessment of carbofuran degradation by earthworm gut-associated Bacillus paralicheniformis PPH2.

The environmental persistence of carbofuran, a potent methylcarbamate neurotoxin, necessitates the development of advanced biotechnological strategies to safeguard soil biodiversity. This study investigated the bioremediation potential of Bacillus paralicheniformis PPH2, a specialized symbiont isolated from a unique ecological niche, the gastrointestinal tract of the indigenous paddy field earthworm Glyphidrilus sp. Unlike traditional soil isolates, strain PPH2 exhibited superior metabolic resilience, growing on carbofuran as the sole carbon and energy source. Through Central Composite Design coupled with Response Surface Methodology, catabolic efficiency was optimized at pH 7.1, 34.7 °C, and 100 rpm, resulting in a validated degradation efficiency of 62.07 ± 1.12% within 120 h. LC-MS/MS analysis revealed the putative identification of carbofuran phenol (m/z 164.36) as the primary biotransformation intermediate, indicating that strain PPH2 likely initiates hydrolytic cleavage of the toxicophoric methylcarbamate ester bond. While the achieved biodegradation efficiency (62.07 ± 1.12%) in unsupplemented minimal medium remains modest compared to specialized multi-strain consortia, it provides substantial acute detoxification, demonstrated by a 1.66-fold reduction in 96-h acute lethality (LC50 increasing from 5.458 to 9.061 mg a.i./kg) in the sentinel earthworm Eisenia fetida. Collectively, this study provides evidence supporting a potential strategy for improving soil health and safeguarding terrestrial ecosystems from pesticide-associated toxicity by bridging microbial kinetics, statistical optimisation, and quantitative ecotoxicology.