Effect of Humic Acids on Biofilm Formation on Polyethylene Surface and Its Biodegradation by Soil Bacteria

The effect of humic acids on the formation of multispecies biofilms on the surface of high-pressure polyethylene and on the initial stages of its biocorrosion has been studied. The ability to form biofilms on the polyethylene surface and the initial stages of its biodegradation have been analyzed for two bacterial communities (binary and multispecies) isolated from the surface of polyethylene incubated in the topsoil (0-5-cm layer) in Myanmar during 180 days. Polyethylene samples were transported under sterile conditions to a laboratory (Moscow) and placed in vials with liquid medium (LB diluted 50 times by mineral medium M9 and with 0.1% C-11-C-16 paraffin solution added as an additional carbon source). Cultures were then disseminated to obtain individual colonies. Humic acids were extracted by alkaline extraction from the upper horizons of ferrallitic soil, in which the polyethylene sample was incubated (Myanmar), and from typical chernozem sampled in Lipetsk oblast (Orthic Acrisol and Haplic Chernozem according to the World Reference Base for Soil Resources, 2014). Humic acids were extracted from humate fertilizer Fleksom based on lowland peat. We assessed the formation of biofilms on the polyethylene surface by staining with crystal violet and changes in the polyethylene surface after the removal of biofilms by densitometric method. The stimulating effect of humic acids of a wide concentration range on the biofilm growth on the polyethylene surface and at the initial stage of its biodegradation has been revealed for the first time. The methodological approaches and the results obtained supplement the information on polyethylene biodegradation and can be applied in biotechnologies.