Negative effect of copper nanoparticles on the conjugation frequency of degradative catabolic plasmid

Abstract

Due to their antimicrobial properties Copper nanoparticles (CuNps) have been proposed to be used in agriculture for pest control. Pesticides removal is mainly done by microorganisms, whose genes usually are found in degradative plasmids transferable by conjugation. Our objective was to evaluate if subinhibitory concentrations of CuNps affect the conjugation frequency (CF) of two degradative plasmids, pJP4 and pADP1. CuNps were characterized by scanning electron microscopy with X-ray detector, dynamic light scattering and atomic absorption spectrophotometry. Mating pairs were incubated in liquid media supplemented with subinhibitory concentrations of CuNps (nominal size 40-60 nm) or copper sulphate (CuSO4) as salt form. Transconjugants strains were checked for pesticide degradation and presence of plasmidial genes by PCR. CuNps dissolution in LB broth were quickly (less 3 h), meanwhile in saline medium without organic matter dissolution never pass over 20%. Neither nanoparticles nor copper salt modify the bacterial growth under subinhibitory concentrations assessed. However, under low concentrations of both copper forms (20 µg mL-1), the conjugation frequencies of degradative plasmids were reduced to 90 %. Therefore, our results indicate that ionic copper affect transference of catabolic plasmids as a subinhibitory consequence. The intentional or accidental release of copper to the environment would be affecting the biodegradative potential of microbial communities and inevitably producing as a result a decrease in the pesticides removal.