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This article reports on the ability of yeast Trichosporon asahii B1 biofilm-associated cells, compared with that of planktonic cells, to transform sec-hexylbenzene and its metabolites. This B1 strain was isolated from a petroleum-polluted sediment collected in the QuangNinh coastal zones in Vietnam, and it can transform the branched aromatic hydrocarbons into a type of forming biofilm (pellicle) more efficiency than that the planktonic forms can. In the biofilm cultivation, seven metabolites, including acetophenone, benzoic acid, 2,3-dihydroxybenzoic acid, β-methylcinnamic acid, 2-phenylpropionic acid, 3-phenylbutyric acid, and 5-phenylhexanoic acid were extracted by ethyl acetate and analyzed by HPLC and GC-MS. In contrast, in the planktonic cultivation, only three of these intermediates were found. An individual metabolite was independently used as an initial substrate to prove its degradation by biofilm and planktonic types. The degradation of these products indicated that their inoculation with B1 biofilms was indeed higher than that observed in their inoculation with B1 planktonic cells. This is the first report on the degradation of sec-hexylbenzene and its metabolites by a biofilm-forming Trichosporon asahii strain. These results enhance our understanding of the degradation of branched-side-chain alkylbenzenes by T. asahii B1 biofilms and give a new insight into the potential role of biofilms formed by such species in the bioremediation of other recalcitrant aromatic compounds.

In this study, three good biofilm-forming yeast strains, including Candida viswanathii TH1, Candida tropicalis TH4 and Trichosporon asahii B1, were isolated from oil-contaminated water and sediment samples collected in coastal zones of Vietnam. These strains were registered in the GenBank database with the accession numbers JX129175, JX129176 and KC139404 for strain TH1, TH4 and B1, respectively. The biofilm formed by a mixture of these organisms degraded 90, 85, 82 and 67% of phenol, naphthalene, anthracene and pyrene, respectively, after a 7-day incubation period using an initial concentration of 600 ppm phenol and 200 ppm of each of the other compounds. In addition, this biofilm completely degraded these aromatic compounds, which were from wastewater collected from petroleum tanks in Do Xa, Hanoi after 14 days of incubation based on gas chromatography mass spectrometry analysis. To the best of our knowledge, reports on polycyclic aromatic hydrocarbon and phenol degradation by biofilm-forming yeasts are limited. The results obtained indicate that the biofilm formed by multiple yeast strains may considerably increase the degradation efficiency of aromatic hydrocarbon compounds, and may lead to a new approach for eliminating petroleum oil-contaminated water in Vietnam.

This work is aimed to assess the aerobic biotransformation of a branched side chain alkylbenzene, iso-pentylbenzene, by Candida viswanathii TH1. The yeast Candida viswanathii TH1 isolated from oil-polluted sediments collected in coastal zones in Vietnam exhibited as a strain that could better transform branched aromatic hydrocarbons in biofilm (pellicle) than in planktonic form. During incubation of TH1 as biofilm with iso-pentylbenzene, the seven intermediates produced were benzoic acid, phenylacetic acid, 2-methyl-4-phenyl-butan-1-ol, 2-hydroxy-phenylacetic acid, 2-methyl-4-phenylbutyric acid, succinic acid and iso-valerophenone as revealed by gas chromatography/mass spectra and high-performance liquid chromatography analyses. The occurrence of these intermediates showed that iso-pentylbenzene could be oxidized not only via mono- but also by a sub-terminal oxidation pathway. This is the first study on iso-pentylbenzene transformation by a biofilm-forming Candida viswanathii strain. The catabolic versatility of the biofilm-forming strain TH1 and its use for mono and sub-terminal oxidation during the transformation of iso-pentylbenzene enhance our understanding of the degradation of branched side chain phenylalkanes and give new insight into the potential role of such species in the transformation of other recalcitrant aromatic compounds.