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A microbial library composed of 416 strains was selected from public collections. The selection was based on the criteria of the highest biodiversity achievable, being finally composed of 71 bacteria strains, 45 actinomycetes, 59 yeasts, 148 filamentous fungi, 33 marine fungi and 60 basidiomycetes. This set of microorganisms was used for a screening campaign searching for microbial biocatalysts for the stereoselective reduction of carbonylic compounds. All the microorganisms mentioned are mesophilic considering their optimal growth requirements. Gongronella butleri, Diplogelasinospora grovesii and Schizosaccharomyces octosporus were selected as the most interesting strains according to their productivity, their tolerance to high concentrations of ketones and the absence of secondary products in the reduction of cycloalkanones. The reduction of (4R)- or (4S)-carvones showed that the stereochemistry of the ketones determine the reduction pathway. Indeed, while (4S)-carvone yields the (2R)-alcohol, the (4R)-carvone carries to dihydrocarveol. D. grovesii and S. octosporus were the strains that displayed better selectivity. The use of resting cells conditions or the lyophilised whole cells reduce the catalytic activity. We describe for the first time a strain, D. grovesii IMI 171018, that is able to produce (2R,4S)-carveol from (4S)-carvone with good yields and enantiomeric excess (ee). |
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