Biodegradation of diesel and heating oil by Acinetobacter calcoaceticus MM5: its possible applications on bioremediation

Twenty aerobic bacterial strains were isolated from altered heating oil. Among them the strain catalogued as MM5 and identified as Acinetobacter calcoaceticus is able to grow on hydrocarbon substrates. When strain MM5 was grown on heating oil, crude oil and tetradecane, increases of protein concentration and of caprilate-lipase and acetate-esterase enzymatic activities were observed in the culture filtrate, with a simultaneous pH drop. A strong emulsification of petroleum by-products was also noticed. Degradation of heating oil was followed by gas chromatography and infrared spectroscopy. Presence of available nitrogen and phosphorus sources were essential for hydrocarbon biodegradation. Intracellular electron transparent inclusions were observed by transmission electron microscopy when strain MM5 cells were grown on hydrocarbons. Light and scanning electron microscopy showed bacteria interconnected by an extracellular polymer and attached to hydrocarbon droplets and to sheets of polymeric material. A bioemulsifier was extracted from the cell-free culture supernatants of strain MM5 grown on tetradecane. The emulsifier is a high molecular weight product that comprises proteins, sugars and fatty acids and which is resistant to high temperature. Strain MM5 should be helpful for the design of strategies for the bioremediation of hydrocarbon contaminated sites.