Interactions of polycyclic aromatic hydrocarbons and their nitro derivatives with bilayer and monolayer models of fungal membranes

Polycyclic aromatic hydrocarbons (PAH) are ubiquitous persistent organic pollutants forming as byproducts in combustion processes. These compounds can become nitrated in the environment forming even more toxic nitro derivatives. Both PAHs and nitro-PAHs accumulate in the soils which can lead to the pollution of vast areas of arable land. The best means of their elimination from the environment is bioremediation that is the degradation by soil microorganisms. Important key players with high prospects are non-ligninolytic fungi, which can incorporate PAHs and their derivatives into their plasma membranes, oxidize and metabolize to nontoxic products. The accumulation of PAHs in the membrane can, however, be toxic to the fungal cell, but the mechanisms of the PAH-membrane lipid interactions and how they influence the membrane phase state and properties are still poorly understood. To shed light on these questions we employed fungal plasma membrane models and studied their interactions with selected PAHs and nitro-PAHs. Two complementary model systems were investigated: giant unilamellar vesicles (GUV) and Langmuir monolayers. We find that the native PAHs induce phase separation and the formation of solid ordered phase in the GUVs, whereas the nitro-derivatives do not disturb the liquid crystalline state of the membranes. The Langmuir monolayer studies indicate that some PAHs preferably partition in the liquid-expanded phase while others in the liquid-condensed domains. The possibility of the incorporation of PAHs into the condensed domains implies that these compounds can influence the order in the lipid bilayer and affect the function of the lipid rafts in plasma membranes.