Organophosphate Hydrolase-Mediated Chlorpyrifos Transformation and Chromium Biodetoxification by Indigenous Planomicrobium sp. A9 From Co-Contaminated Haryana Soils: Enzyme Confirmation, TCP Metabolite Tracking and Oxidative-Stress Characterization

Abstract

Co-contaminated soils bearing simultaneous heavy metal and organophosphate pesticide loads present a toxicological complexity that single-contaminant bioremediation frameworks cannot adequately address. This study applies a two-block evidence framework to Planomicrobium sp. A9, an indigenous isolate from industrially co-contaminated soils of Haryana, India. The first block quantifies the oxidative-stress response: malondialdehyde reached 58.27 µmol mg⁻¹ protein, while SOD inhibition (3.91%), catalase activity (k = 0.040 s⁻¹ mL⁻¹) and reduced glutathione (0.4 nM mg⁻¹ protein) were measurable but low, consistent with partial antioxidant depletion under chronic multi-contaminant stress. The second block provides direct transformation evidence: OPH/phosphotriesterase specific activity of 0.045 U mg⁻¹ protein (44.7-fold above heat-inactivated control) and esterase activity of 0.155 U mg⁻¹ protein (8.6-fold above control) confirms enzyme-linked organophosphate bond cleavage. Targeted GC-MS monitoring of chlorpyrifos and its primary metabolite TCP showed transient accumulation peaking at 2.74 mg L⁻¹ at 24 h before declining to 0.16 mg L⁻¹ by 72 h, kinetically distinguishing active enzymatic hydrolysis from abiotic loss. A diphenylcarbazide colorimetric assay confirmed 69.2% Cr(VI) reduction within 48 h, independently corroborating ICP-MS total chromium data (68.09%) from the companion study. KEGG pathway analysis contextualized TCP kinetics within the documented OPH-initiated hydrolytic route. Six convergent evidence layers establish Planomicrobium sp. A9 as an enzymatically competent, multi-stress-adapted candidate for bioremediation of mixed heavy metal–pesticide environments, constituting, to our knowledge, the first enzyme-level and metabolite-tracking characterization of this bacterial isolate under authentic industrial co-contamination conditions.