Abstract
Agro-industrial side streams such as oilseed cakes were used as a medium in solid-state fermentation (SSF) for microbial oxidation of anti- and syn-3-methyl-octane-1,4-diols to obtain corresponding trans- and cis-whisky lactones. In preliminary screening transformations, a wide range of whole bacterial cells were tested on the basis of oxidation activity, which is rarely described in the literature, in contrast to the widely studied lipolytic activity on SSF. Among the different oil cakes tested, biotransformations carried out on linseed cake were characterized by the highest conversion and stereoselectivity. Several preparative-scale oxidations performed in a self-constructed SSF bioreactor catalyzed by Rhodococcus erythropolis DSM44534, Rhodococcus erythropolis PCM2150 and Gordonia rubripertincta PCM2144 afforded optically active trans-(+)-(4S,5R), cis-(+)-(4R,5R) and cis-(-)-(4S,5S) isomers of whisky lactones, respectively. Bacteria of the Rhodococcus, Gordonia, Dietzia and Streptomyces genera carried out transformations with complete conversion after three days. Various extraction methods were applied for the isolation of the products, and among them, the combination of steam distillation with simple extraction were the most efficient. Biotransformations were conducted under precise control of conditions in a bioreactor based on a Raspberry Pi Zero W. The proposed low-cost (ca. USD 100) bioreactor is a standalone system that is fully autoclavable and easy to use.
Highlights
Solid-state fermentation (SSF) is defined as a microbial cultivation process conducted on a solid substrate with a low content of water [1]
The reaction mixture was shaken with solvent for 4 h, and the organic phase was filtered under reduced pressure
The byproducts from the oil industry can be used as a valuable microbial medium for the bacterial oxidation process, leading from diols to whisky lactones
Summary
Solid-state fermentation (SSF) is defined as a microbial cultivation process conducted on a solid substrate with a low content of water [1]. Oxidation with Gordonia bronchialis PCM2167 on linseed cake afforded optically active trans-(+)-(4S,5R)-isomer (2a) (81–83%, ee = 33%) and enantiomerically pure cis-(−)-(4S,5S) whisky lactone (2c) (17–19%, ee >99%). In biotransformations performed on linseed cake with Rhodococcus erythropolis DSM44534, R. rhodochrous PCM909 and R. ruber PCM2166, optically active trans-whisky lactone isomers were obtained after three days in amounts of 97%, 92% and 92%, respectively. In biotransformations performed on the linseed cake with G. bronchialis PCM2167, R. ruber PCM2166, R. erythropolis DSM44534 and R. rhodochrous PCM909 (2.1 and 2.2), significantly more trans whisky lactone (81–97%) was formed when anti-3-methyl-octane1,4-diol (1a) was used as a substrate (Table 1). During biotransformation of anti- and syn-diols with strains Dietzia maris PCM2292 and Rhodococcus rhodnii PCM2157 (not mentioned in Tables 4 and 5), there was no conversion, which proves that these bacteria do not have the ability to oxidize 3-methyl-octane-1,4-diol on linseed cake. R. erythropolis PCM2150 catalyzed oxidation of syn-diol to only cis-lactone, while from anti-diol a mixture of cis/trans-whisky isomers was detected
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