Isolation of a novel yeast strain Candida digboiensis TERI ASN6 capable of degrading petroleum hydrocarbons in acidic conditions

A novel yeast species Candida digboiensis TERI ASN6 was isolated from soil samples contaminated with acidic oily sludge (pH 1–3) from the Digboi refinery (Northeast India). The strain TERI ASN6 could degrade 73% of the total petroleum hydrocarbons present in the medium at pH 3 in a week. This strain presents a dimorphic behaviour and showed mycelia morphology when grown under stressed conditions such as low pH and in a medium containing petroleum hydrocarbons. The C. digboiensis strain could efficiently degrade the aliphatic and aromatic fractions of the acidic oily sludge at pH 3 as confirmed by gas chromatography. During the growth of TERI ASN6 in dibenzothiophene (DBT), DBT-sulfone and biphenyl-2-ol were detected. An active cytochrome P450 system, implicated in hydrocarbon oxidation, was also detected in this yeast using degenerated primers based on its conserved regions. This yeast is a potential candidate for petroleum bioremediation treatment of hydrocarbon contaminated acidic soils. Its physiological behaviour allows the strain to work efficiently where other hydrocarbon-degrading bacteria may not survive.