No abstract

In this study, biodesulfurization (BDS) was carried out using immobilized Rhodococcus erythropolis KA2-5-1 in n-tetradecane containing dibenzothiophene (DBT) as a model oil (n-tetradecane/immobilized cell biphasic system). The cells were immobilized by entrapping them with calcium alginate, agar, photo-crosslinkable resin prepolymers (ENT-4000 and ENTP-4000), and urethane prepolymers (PU-3 and PU-6); and it was found that ENT-4000-immobilized cells had the highest DBT desulfurization activity in the model oil system without leakage of cells from the support. Furthermore, ENT4000-immobilized cells could catalyze BDS repeatedly in this system for more than 900 h with reactivation; and recovery of both the biocatalyst and the desulfurized model oil was easy. This study would give a solution to the problems in BDS, such as the troublesome process of recovering desulfurized oil and the short life of BDS biocatalysts.

No abstract

Thirty-five bacterial strains capable of converting dibenzothiophene into 2-hydroxybiphenyl were isolated. Among them Rhodococcus erythropolis KA2-5-1 was chosen for further characterization because of its ability to retain high desulfurization activity stably. PCR cloning and DNA sequencing of a KA2-5-1 genomic DNA fragment showed that it was practically identical with dszABC genes from Rhodococcus sp. IGTS8, a representative carbon-sulfur-bond-targeted dibenzothiophene-degrading bacterium. KA2-5-1 desulfurized a variety of alkyl dibenzothiophenes through the specific cleavage of their C-S bonds. In addition, unexpectedly, KA2-5-1 also attacked alkyl benzothiophenes in a C-S-bond-targeted fashion. The purified monooxygenase, encoded by dszC of KA2-5-1, converted benzothiophene and dibenzothiophene into benzothiophene sulfone and dibenzothiophene sulfone, respectively, with the aid of an NADH-dependent oxidoreductase. This result raises the possibility that the same enzymatic step may be involved in desulfurization of alkylated forms of both dibenzothiophene and benzothiophene in KA2-5-1 cells.