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Biotechnol Bioeng. 2014 May;111(5):876-84. doi: 10.1002/bit.25148. Epub 2013 Nov 27.

Rate-limiting step analysis of the microbial desulfurization of dibenzothiophene in a model oil system.

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Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, 02139.


A mechanistic analysis of the various mass transport and kinetic steps in the microbial desulfurization of dibenzothiophene (DBT) by Rhodococcus erythropolis IGTS8 in a model biphasic (oil-water), small-scale system was performed. The biocatalyst was distributed into three populations, free cells in the aqueous phase, cell aggregates and oil-adhered cells, and the fraction of cells in each population was measured. The power input per volume (P/V) and the impeller tip speed (vtip ) were identified as key operating parameters in determining whether the system is mass transport controlled or kinetically controlled. Oil-water DBT mass transport was found to not be limiting under the conditions tested. Experimental results at both the 100 mL and 4 L (bioreactor) scales suggest that agitation leading to P/V greater than 10,000 W/ m(3) and/or vtip greater than 0.67 m/s is sufficient to overcome the major mass transport limitation in the system, which was the diffusion of DBT within the biocatalyst aggregates.


Rhodococcus erythropolis IGTS8; aggregation; biodesulfurization; dibenzothiophene; power input per volume; rate-limiting step

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