Biodesulfurization of Dibenzothiophene by Microbial Cells Coated with Magnetite Nanoparticles

Microbial cells of Pseudomonas delafieldii were coated with magnetic Fe₃O₄ nanoparticles and then immobilized by external application of a magnetic field. Magnetic Fe₃O₄ nanoparticles were synthesized by a coprecipitation method followed by modification with ammonium oleate. The surface-modified Fe₃O₄ nanoparticles were monodispersed in an aqueous solution and did not precipitate in over 18 months. Using transmission electron microscopy (TEM), the average size of the magnetic particles was found to be in the range from 10 to 15 nm. TEM cross section analysis of the cells showed further that the Fe₃O₄ nanoparticles were for the most part strongly absorbed by the surfaces of the cells and coated the cells. The coated cells had distinct superparamagnetic properties. The magnetization (δ_s) was 8.39 emu · g⁻¹. The coated cells not only had the same desulfurizing activity as free cells but could also be reused more than five times. Compared to cells immobilized on Celite, the cells coated with Fe₃O₄ nanoparticles had greater desulfurizing activity and operational stability.