Isolation of biosurfactant-producing and crude oil-degrading bacterium, Enterococcus hirae, from hydrocarbon-polluted soils and characterization of the biosurfactant produced

Abstract

The spillage of petroleum hydrocarbons into our environment causes a lot of disastrous environmental pollution. The employment of biosurfactant-producing and hydrocarbon-utilizing microorganisms enhances the effectiveness of bioremediation of these toxic pollutants. This study was aimed at isolating biosurfactant-producing and crude oil degrading
bacteria from hydrocarbon-polluted soils and characterization of the biosurfactant produced. The biosurfactant screening techniques employed were haemolysis assay, drop collapse test, oil displacement test, tilting glass test and emulsification index (E24) test. The degradation rate of the most potent crude oil degrader was determined using gravimetric method and Gas Chromatography – Mass Spectroscopy (GC-MS) analysis. The bacterium was identified based on phenotypic, biochemical and molecular analyses. Fourier Transform Infra-Red (FTIR) and GC-MS analyses were used to characterize the biosurfactant produced. A potent bacterium, Enterococcus hirae (identified by 16s rDNA sequencing) was isolated from hydrocarbon contaminated soil and it could degrade 77.2% of total petroleum hydrocarbons after two weeks of culture when grown in mineral salt medium (MSM) supplemented with 2% (v/v) crude oil as the sole carbon source. Chromatogram of the treated crude revealed that E. hirae could potentially degrade various hydrocarbon contents (C21 – C35) present in the crude oil. The biosurfactant produced was characterized as Glycolipids (Rhamnolipids) using FTIR and GC-MS analyses. This study demonstrates E. hirae as an efficient biosurfactant producer and crude oil degrader. To the best of the researchers’ knowledge, this is the first time E. hirae is reported as both biosurfactant producers and crude oil degrader.