Biotransformation of cyclohexanone using immobilized Geotrichum candidum NCYC49: Factors affecting the selectivity of the process

A screening of 416 microorganisms belonging to different taxonomical groups (bacteria, actinomycetes, yeasts and filamentous fungi) was performed looking for strains with high ketone monooxygenase activity. After that screening, the strain Geotrichum candidum NCYC49 was selected on the basis of the production of moderate yields of caprolactone from cyclohexanone, as well as the reproducibility of its culture conditions. Several strategies were followed in order to favor the monooxygenation reaction: growing cells, resting cells, lyophilized cells, and immobilization in different matrices (Pterocladia agar, calcium alginate, polyacrylamide). Interestingly, the results obtained by immobilization in polyacrylamide or in Pterocladia agar indicate that a complete separation of the reduction and monooxygenation activities can be achieved by controlling the oxygenation conditions. Thus, reactions carried out in high oxygenation conditions (high shaking speed or low matrix concentration) displayed a very high yield in caprolactone (90–100% conversion) without detectable production of cyclohexanol. On the contrary, reactions carried out under low oxygenation conditions clearly favored the production of cyclohexanol (reduction reaction), particularly when agar was used as a matrix.