Asphaltene biotransformation by a novel enzyme thiol peroxidase from Micrococcus sp. IITD107.

Abstract

Asphaltenes are known to cause high density and viscosity in heavy crude oil. The gene for thiol peroxidase was found to be present in five members of the nine-membered bacterial consortium able to biotransform about 75% of asphaltenes. Here, we report cloning, expression, purification, and detailed characterization of a thiol peroxidase enzyme from one of the consortium members, Micrococcus sp. IITD107. Asphaltene was treated with the crude cell lysate obtained after overexpression of thiol peroxidase from heterologous host Escherichia coli as well as with purified enzyme. A significant reduction in the major peaks obtained by gas chromatography mass spectrometry (GC-MS) of asphaltene was observed, corresponding to small polyaromatic hydrocarbons such as benzaldehyde, phenol-methylethylidene, benzenepropionic acid, and linear aliphatic chains such as heptadecane, tetradecane, octadecane, etc. Changes in the structure of asphaltene were also observed in the Fourier transform infrared spectroscopy and nuclear magnetic resonance spectra. The elemental analysis determined around 60% reduction in sulfur and 69% reduction in nitrogen. A decrease in aromaticity of asphaltene was also observed. Scanning electron microscopy imaging of the treated asphaltene fraction captured during the course of biotransformation revealed formation of pores in the structure. This is the first report demonstrating the use of thiol peroxidase for asphaltene biotransformation. The enzyme can also be used for the biological synthesis of porous carbon, which has not been reported to date.IMPORTANCEHeavy crude oil is abundant but contains asphaltene, which results in its high density and viscosity, making it unsuitable for commercial application. The removal of asphaltene leads to a reduction in heaviness of the oil and renders it light and suitable for commercialization. Asphaltene is a complex and large polyaromatic hydrocarbon consisting of several heteroatoms. The use of enzymatic biotransformation of asphaltene aids in breaking down the complex molecule into smaller moieties without affecting the calorific value. This study helps in identifying a novel enzyme thiol peroxidase for biotransformation of asphaltene and valorization of asphaltene to synthesize porous carbon.