Isolation and molecular genetic characterization of a yeast strain able to degrade petroleum polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) belong to a class of toxic environmental pollutants and PAH exposure causes public health risks and raises environmental concerns. Identification of the key microorganisms that play a role in pollutant degradation processes is relevant to the development of optimal in situ bioremediation strategies. In the current study, three yeast strains were isolated from oil-contaminated soil by enrichment technique in mineral basal salts (MBS) medium supplemented with phenanthrene as a sole carbon source. Out of these, strain AH70 was selected for PAHs degradation, because of its fast growth on agar plate coated by PAHs as sole source of carbon and energy. The yeast was identified by molecular genetics technique based on sequence analysis of the variable D1/D2 domain of the large subunit (26S) ribosomal DNA. Subsequent 26S rRNA gene sequencing showed 100% base sequence homology and it was identified as Candida viswanathii. The degradation of PAHs by this yeast was confirmed by GC-MS analyses. The yeast was capable of degrading a mixture of low and high molecular weight PAHs and degradation efficiency was found as 89.76% for naphthalene, 77.21% for phenanthrene, 60.77% for pyrene and 55.53% for benzo(a) pyrene at the end of 10 days.