Top-down/bottom-up consortia achieve robust γ-HCH degradation and reduced methanogenic contribution in wetlands

ABSTRACT Generalist non-obligate organochlorine-degrading bacteria (ODB) play an important role in the bioremediation of γ-hexachlorocyclohexane (γ-HCH), yet their ecological roles and functional mechanisms remain underexplored. In this study, we used both “top-down” and “bottom-up” strategies to construct two functional consortia (M and Y13) based on non-obligate ODB. Both consortia demonstrated efficient degradation in sediment microcosms, reducing γ-HCH (C/C₀) to 63.0% (M) and 56.1% (Y13). Simultaneously, functional microbial consortia inoculation significantly suppressed the CO₂ reduction methanogenesis pathway compared with the non-inoculated group ( P < 0.05), as evidenced by a marked decline in the CH₄/CO₂ ratio in inoculated groups. The well-known degradation gene pceA was enriched in the Y13 group, and the co-localization of pceA -encoding contigs with mobile genetic elements was identified. Notably, Enterococcus was found to have successfully colonized inoculated groups. It has strong environmental evolutionary adaptability and might acquire organochlorine-degrading genes through horizontal gene transfer under pollution stress. The broad applicability of non-obligate ODB (e.g., Enterococcus ) makes them a promising candidate for future environmental remediation efforts, breeding new avenues of “One Health” win–win solutions in carbon reduction during pollution remediation for wetlands. IMPORTANCE γ‑Hexachlorocyclohexane (γ‑HCH) is a representative organochlorine pesticide and a well‑known persistent organic pollutant that poses significant risks to ecosystems and human health. Microbial anaerobic degradation is a key process in the natural attenuation and engineered cleanup of γ‑HCH contamination. The effective application of obligate organohalide-respiring bacteria often requires precise management. In parallel, newly discovered non‑obligate organohalide-respiring bacteria capable of degrading γ‑HCH have emerged as promising alternatives, yet their performance and ecological interactions in realistic sediment systems remain poorly understood. This study examines the degradation mechanisms and microbial ecology of non-obligate organohalide-respiring bacterial functional consortia in complex media. The findings provide critical insights for developing effective bioaugmentation strategies for lindane‑contaminated coastal wetlands and may offer a useful framework for managing other recalcitrant halogenated pollutants in similar environments.