Mechanisms of pollution induced community tolerance in a soil microbial community exposed to Cu

• Mechanisms of PICT and co-tolerance examined in field soil.
• Rate of previous exposure to Cu correlated to increased tolerance to new Cu.
• Community tolerance linked with increased metabolic quotient.
• No evidence for co-tolerance to Ag+ or vancomycin.
• Tolerance not due to shifts in community composition or resistance genes.

Pollution induced community tolerance (PICT) to Cu2+, and co-tolerance to nanoparticulate Cu, ionic silver (Ag+), and vancomycin were measured in field soils treated with Cu2+ 15 years previously. EC50 values were determined using substrate induced respiration and correlations made against soil physicochemical properties, microbial community structure, physiological status (qCO2; metabolic quotient), and abundances of genes associated with metal and antibiotic resistance. Previous level of exposure to copper was directly (P < 0.05) associated with tolerance to addition of new Cu2+, and also of nanoparticle Cu. However, Cu-exposed communities had no co-tolerance to Ag+ and had increased susceptibly to vancomycin. Increased tolerance to both Cu correlated (P < 0.05) with increased metabolic quotient, potentially indicating that the community directed more energy towards cellular maintenance rather than biomass production. Neither bacterial or fungal community composition nor changes in the abundance of genes involved with metal resistance were related to PICT or co-tolerance mechanisms.