Dichlorobiphenyls and chlorinated benzoic acids – Emergent soil pollutants in model bacterial membranes. Langmuir monolayer and Grazing Incidence X-ray Diffraction studies

The multi-decade worldwide application of polychlorinated biphenyls (PCB) leads to the problem of soil pollution. The production and application of PCB was banned, so the gradual decrease of their concentration in the soils was expected. On the contrary, novel sources of dichlorobiphenyls as PCB 11 were identified and these emergent pollutants are still emitted to the environment. Dichlorobiphenyls and some chlorobenzoic acids (CBA) are known as dead-end PCB metabolites – they accumulate in the soils and being toxic to microorganisms lead to the impoverishment of soil decomposer consortia. The toxicity of PCB and CBA is connected with their membrane activity and accumulation in the bacterial membranes. The correlation between the phospholipid composition of the bacterial membrane and the toxicity of PCB and CBA is unfortunately unknown limiting the effective selection of bacterial species for bioremediation of polluted soils. To shed light on these phenomena we applied binary phospholipid Langmuir monolayers as model bacterial membranes. With these models we studied the phenomena of dichlorobiphenyls and selected CBA molecules' incorporation and the effects exerted by these molecules on the ordering of the phospholipid molecules at the molecular scale. For the studies of the organization of the model membranes we applied Grazing Incidence X-ray Diffraction. It turned out that the model membranes rich in cardiolipin can accumulate more pollutant molecules than the models containing phosphatidylglycerols. The accumulation of the pollutants did not cause any significant changes in the 2D crystalline structure of the former models whereas the latter were profoundly modified.