Earthworm-assisted enrichment of specific indigenous soil microbes for the preferential degradation of hexaconazole R-enantiomer.

This study examined the influence of earthworm addition on the enantiomer-specific degradation of the chiral triazole fungicide hexaconazole, focusing on the associated functional bacterial communities in soil and earthworm casts. S-hexaconazole was preferentially degraded in soil, whereas R-hexaconazole strongly inhibited soil microbial activities. Earthworm addition preferentially accelerated R-hexaconazole degradation and eliminated its inhibitory effects. Two soil bacterial families, Sphingomonadaceae and Xanthomonadaceae, and two biodegradation genes, p450 and ppo, were associated with the preferential degradation of S-hexaconazole. Two bacterial strains, HEX1 and HEX2, which belong to Sphingomonadaceae and Xanthomonadaceae, respectively, degraded R-hexaconazole but preferentially degraded S-hexaconazole in pure culture. In the R-hexaconazole treatment, earthworms selectively increased the abundances of Sphingomonadaceae, Xanthomonadaceae, and ppo, with Xanthomonadaceae and ppo levels being 23.1% and 25.1% higher, respectively, than those in the S-hexaconazole treatment, thereby shifting the community-level degradation preference toward R-hexaconazole. Notably, similar patterns were observed in earthworm casts. Network and metagenomic binning analyses revealed that Sphingomonadaceae and Xanthomonadaceae were potential hosts of the p450 and ppo. These findings suggest that earthworms facilitate the enrichment of specific indigenous soil bacterial families (Sphingomonadaceae and Xanthomonadaceae) to accelerate the preferential degradation of R-hexaconazole, highlighting the potential of earthworms to mitigate the risks in chiral fungicide-contaminated soil.