Use of hydrophobic bacterium Rhodococcus rhodochrous NBRC15564 expressed thermophilic alcohol dehydrogenases as whole-cell catalyst in solvent-free organic media

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Abstract The hydrophobic bacterium Rhodococcus rhodochrous NBRC15564 was employed as a whole-cell biocatalyst to examine its potential for bioconversion in solvent-free organic media. The genes encoding two different thermostable alcohol dehydrogenases (ADH Tt1 and ADH Tt2 ) of Thermus thermophilus HB27 were expressed in R. rhodochrous cells. To inactivate indigenous mesophilic enzymes in R. rhodochrous , transformant cells were heated at 70 °C for 10 min. Heat-treated hydrophobic wet cells were used for the bioconversion of 2,2,2-trifluoroacetophenone (TFAP) to α-(trifluoromethyl) benzyl alcohol (TFMBA) as a model reaction with ADH Tt1 . NADH, which was supplied in aqueous solution, was regenerated by converting cyclohexanol to cyclohexanone by ADH Tt2 . All reactions were performed by suspending heat-treated cells in solvent-free organic media consisting of 3.7 M TFAP and 4.8 M cyclohexanol (1:1, v/v ratio) at 60 °C. When 800 mg heat-treated R. rhodochrous cells were dispersed in 2 mL of solvent-free organic media (400 mg cells/mL), the product concentration reached about 3.6 M TFMBA by 48 h with a total NADH turnover number of approximately 900. The overall productivity was 190 mol TFMBA/kg cells/h.

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