Interaction between copper and extracellular nucleic acids in the EPS of unsaturated Pseudomonas putida CZ1 biofilm

The role of extracellular DNA (eDNA) in biofilm in heavy metal complexation has been little reported. In this study, the interaction between the extracellular fraction of unsaturated biofilms and Cu²⁺ was studied using random amplified polymorphic DNA (RAPD) and synchrotron-based X-ray absorption spectroscopy (XAS) analyses. Under Cu²⁺ stress, the amount of eDNA was about 10-fold higher than the treatment without Cu²⁺ stress, which was substantially more than the amount of intracellular DNA (iDNA) present in the biofilm. The eDNA content increased significantly under Cu²⁺ stress and higher eDNA contents were found in colloidal extracellular polymeric substances (EPS) than in capsular EPS in Luria-Bertani medium. It was found that the composition of eDNA was distinctly changed under conditions of Cu²⁺ stress compared with the treatments without Cu²⁺ treatments, with specific eDNA bands appearing under Cu²⁺ treatments as revealed by RAPD analyses. X-ray absorption fine structure (XAFS) analysis assessing the molecular speciation of copper showed that copper in the secreted eDNA mainly existed as species resembling Cu₃(PO₄)₂, followed by Cu-citrate species. This study investigated the interaction between copper and eDNA in unsaturated Pseudomonas putida CZ1 biofilms. Potential function of eDNA in biofilms under Cu²⁺ stress was found.