Baldi Franco, Pepi Milva, Fava Fabio
Department of Environmental Sciences, Cà Foscari University, S. Marta, Dorsoduro 2137I-30121 Venice, Italy.
Appl Environ Microbiol. 2003 Aug;69(8):4689-96. doi: 10.1128/AEM.69.8.4689-4696.2003.
Strains DBVPG 6662 and DBVPG 6739 of Rhodosporidium toruloides, a basidiomycete yeast, grew on thiosulfate as a sulfur source and glucose (2 g liter(-1) or 10.75 mM) as a carbon source. DBVPG 6662 has a defective sulfate transport system, whereas DBVPG 6739 barely grew on sulfate. They were compared for the ability to use dibenzothiophene (DBT) and related organic sulfur compounds as sulfur sources. In the presence of glucose as a carbon source and DBT as a sulfur source, strain DBVPG 6662 grew better than DBVPG 6739. In the presence of thiosulfate as a sulfur source, the two yeast strains did not use DBT, DBT-sulfone, benzenesulfonic acid, biphenyl, and fluorene. When the two strains were grown in the presence of glucose, strain DBVPG 6662 transformed 27% of the DBT present (10 micro M) at a rate of 0.023 micro mol liter(-1) h(-1) in 36 h. Traces of 2,2'-dihydroxylated biphenyl were transiently accumulated under these conditions. When the same strain was grown on glucose in the presence of a higher concentration of DBT (0.5 g liter(-1)), mainly in an insoluble form, the whole surface of the DBT crystals was colonized by a thick mycelium. This adherent structure was imaged by confocal microscopy with fluorescent concanavalin A, a lectin that specifically binds glucose and mannose residues. When DBVPG 6662 was grown on glucose in the presence of a commercial emulsion of bitumen, i.e., orimulsion, 68% of the benzo- and dibenzothiophenes and DBTs was removed after 15 days of incubation. The fungus adhered by hyphae to orimulsion droplets. When cultivated in the presence of commercial emulsifier-free fuel oil containing alkylated benzothiophenes and DBTs and having a composition similar to that of orimulsion, strain DBVPG 6662 removed only 11% of the total organic sulfur that occurs in the medium and did not adhere to the oil droplets. These results indicate that strain DBVPG 6662 is able to utilize the organic sulfur of DBT and a large variety of thiophenic compounds that occur extensively in commercial fuel oils by physically adhering to the organic sulfur source.
担子菌酵母红冬孢酵母（Rhodosporidium toruloides）的菌株DBVPG 6662和DBVPG 6739能以硫代硫酸盐作为硫源、葡萄糖（2 g/L或10.75 mM）作为碳源生长。DBVPG 6662的硫酸盐转运系统存在缺陷，而DBVPG 6739在硫酸盐上几乎不生长。对它们利用二苯并噻吩（DBT）及相关有机硫化合物作为硫源的能力进行了比较。在以葡萄糖作为碳源、DBT作为硫源的情况下，菌株DBVPG 6662的生长情况优于DBVPG 6739。在以硫代硫酸盐作为硫源时，这两种酵母菌株不利用DBT、DBT -砜、苯磺酸、联苯和芴。当这两种菌株在葡萄糖存在的条件下生长时，菌株DBVPG 6662在36小时内以0.023 μmol/L·h-1的速率转化了27%的存在的DBT（10 μM）。在这些条件下会短暂积累痕量的2,2'-二羟基联苯。当同一菌株在较高浓度的DBT（0.5 g/L）存在的情况下于葡萄糖上生长时，DBT晶体的整个表面都被一层厚厚的菌丝体定殖。这种附着结构通过共聚焦显微镜用荧光伴刀豆球蛋白A成像，伴刀豆球蛋白A是一种特异性结合葡萄糖和甘露糖残基的凝集素。当DBVPG 6662在含有沥青商业乳液（即奥里乳化油）的葡萄糖上生长时，培养15天后，68%的苯并噻吩、二苯并噻吩和DBT被去除。真菌通过菌丝附着在奥里乳化油滴上。当在含有烷基化苯并噻吩和DBT且组成与奥里乳化油相似的无商业乳化剂燃料油存在的情况下培养时，菌株DBVPG 6662仅去除了培养基中总有机硫的11%，并且不附着在油滴上。这些结果表明，菌株DBVPG 6662能够通过物理附着在有机硫源上，利用DBT的有机硫以及商业燃料油中广泛存在 的多种噻吩类化合物。
