Promoting chiral metalaxyl degradation by bioaugmentation with a host-guest soil microbial consortium

Background Bioaugmentation with isolated pollutant-degrading strains is often limited by their poor establishment in native soils. The present study tested the hypothesis that introducing an active “guest” soil with high rac-metalaxyl-degrading capacity into a poorly degrading “host” soil would promote the establishment of degrading microorganisms, reshape the bacterial community, and enhance enantioselective transformation. Methods Host soil (S1) and guest soil (S2) were mixed at various ratios and preincubated for different durations. Microbial biomass carbon (MBC), soil enzyme activities, bacterial community characteristics, and rac-metalaxyl transformation kinetics were evaluated. Results Soil mixing increased MBC by 10%–15% compared with values predicted from proportional contributions of the individual soils, and bacterial richness in host–guest soils exceeded that of either native soil. Selected enzyme activities and the relative abundances of dominant bacterial phyla responded nonlinearly to the guest soil proportion. Bacterial community dissimilarity increased logarithmically with the proportion of guest soil, maintaining a distinct community structure even after 120 days of preincubation. In the 4:1 host–guest mixture, the initial transformation rate (r 0 ) reached 48% and 71% of that in guest soil S2 after 14 and 120 days of preincubation, respectively. Transformation enantioselectivity was more closely associated with bacterial community structure than with richness. Conclusion Active soil can serve as a functionally stable whole-community inoculum, offering a practical bioaugmentation strategy when the establishment of single isolated strains is constrained.