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Environmental regulations on sulfur contents have prompted researches on deep desulfurization for near-zero sulfur (< 1 ppm) ultra-clean fuels.Biodesulfurization (BDS) is a non-destructive approach that can specifically remove sulfur from refractory hydrocarbons under mild conditions.There are some bottlenecks limiting the commercialization of the BDS process.When free cells were used for petroleum BDS, deactivation of the biocatalyst and troublesome of oil-water-biocatalyst separation are significant barrier.Cell immobilization may give a solution to the problems, providing advantages such as repeated or continuous use, enhanced stability and easy separation.In this paper, a novel in situ cell separation and immobilization method for DBT BDS was developed by using superparamagnetic Fe3O4 (NPs).The Fe3O4 NPs were synthesized by coprecipitation method followed by modification with ammonium oleate.The surface-modified NPs were monodispersed and the particle size was about 13 nm with 50.8 emu/g saturation magnetization.After adding the magnetic fluids to the culture broth, Rhodococcus erythropolis LSSE8-1 cells were adsorptive immobilized and then separated with an externally magnetic field.The maximum adsorption amount was about 530 g dry cell weight/g particles to LSSE8-1 cells.Compared to the reusable limitation of free cells, the coated cells not only had the same desulfurizing activity as free cells but also could be easily separated from fermentation broth by magnetic force.