Winter bioaugmentation of co-contaminated soil: Differential effects in greenhouse and open-field settings on microbial communities

Abstract

This study evaluated a winter bioaugmentation strategy using the psychrotolerant strain Microbacterium arborescens SMB19 to remediate antibiotic–heavy metal co-contaminated soils and examined its effects on microbial community functions under two contrasting environments: greenhouse warming (WTM) and open-field non-warming (CTM). Results showed that SMB19 effectively reduced antibiotic residues and bioavailable Zn concentrations. Under CTM, remediation was more effective, with higher antibiotic degradation rates and greater reductions in bioavailable metals. However, the abundance of mobile genetic elements (MGEs) and antibiotic resistance genes (ARGs) increased. In contrast, under WTM, the synergistic effect between SMB19 and indigenous microbes was weaker, but the ARG and MGE levels significantly decreased. Mantel test results revealed a stronger correlation between ARGs and microbial communities in the WTM. Network analysis showed that microbial functional groups were more dispersed in the WTM than in the highly clustered structure observed in the CTM. Functionally, CTM-enriched microbial taxa were involved in pollutant remediation and element cycling, whereas WTM-favored taxa were related to nitrogen cycling and greenhouse-specific adaptations. Functional predictions further indicated that WTM enhanced antibiotic biosynthesis pathways and CTM promoted organic matter degradation. These findings suggest that exogenous bacteria-based bioaugmentation holds great promise for cold-region soil remediation; however, greenhouse conditions must be carefully optimized to balance pollutant removal efficiency and the risk of ARG dissemination.