The use of free and immobilised Arthrobacter simplex in organic solvent/aqueous two-liquid-phase reactors

The use of free and immobilised Arthrobacter simplex (NCIB 8929) for steroid delta 1-dehydrogenation in two-liquid-phase, stirred-tank reactors has been compared. Product formation is related to the logarithm of the water-octanol partition coefficient (log P) of the organic solvent employed, but the relationship is different for the two forms of the biocatalyst. No reaction was seen with either biocatalyst in media containing solvents of log P less than or equal to 2.5. For free bacteria, product formation rose linearly with log P thereafter to a maximum at a value of 9.8. With immobilised bacteria, product formation reached a maximum with a solvent of log P = 4.0 and remained constant with solvents of higher log P value. Consequently extended reactor operation was possible with immobilised bacteria, and the production of high quality (greater than 95% purity) steroid product was demonstrated.