hornekiae 15A gave highly stereoselective reduction of (R,S)-1, while H. aquamarina 9B enantioselectively hydrolysed (R,S)-1; in both the cases, enantiomerically pure unreacted substrate could be easily recovered and purified at molar conversion below 57-58%, showing the potential of DHABs extremophile microbiome and marine-derived enzymes in biocatalysis.

The use of seawater and marine microorganisms can represent a sustainable alternative to avoid large consumption of freshwater performing industrial bioprocesses. Debaryomyces hansenii, which is a known halotolerant yeast, possess metabolic traits appealing for developing such processes. For this purpose, we studied salt stress exposure of two D. hansenii strains isolated from marine fauna. We found that the presence of sea salts during the cultivation results in a slight decrease of biomass yields. Nevertheless, higher concentration of NaCl (2 M) negatively affects other growth parameters, like growth rate and glucose consumption rate. To maintain an isosmotic condition, the cells accumulate glycerol as compatible solute. Flow cytometry analysis revealed that the osmotic adaptation causes a reduced cellular permeability to cell-permeant dye SYBR Green I. We demonstrate that this fast and reversible phenomenon is correlated to the induction of membrane depolarization, and occurred even in presence of high concentration of sorbitol. The decrease of membrane permeability induced by osmotic stress confers to D. hansenii resistance to cationic drugs like Hygromycin B. In addition, we describe that also in Saccharomyces cerevisiae the exposure to hyper-osmotic conditions induced membrane depolarization and reduced the membrane permeability. These aspects are very relevant for the optimization of industrial bioprocesses, as in the case of fermentations and bioconversions carried out by using media/buffers containing high nutrients/salts concentrations. Indeed, an efficient transport of molecules (nutrients, substrates, and products) is the prerequisite for an efficient cellular performance, and ultimately for the efficiency of the industrial process.

A recombinant ketoreductase from Pichia glucozyma (KRED1-Pglu) was used for the enantioselective reduction of various mono-substituted acetophenones. Reaction rates of meta-and para-derivatives were consistent with the electronic effects described by σ-Hammett coefficients; on the other hand, enantioselectivity was determined by an opposite orientation of the substrate in the binding pocket.Reduction of ortho-derivatives occurred only with substrates bearing substituents with low steric impact (i.e., F and CN). Reactivity was controlled by stereoelectronic features (CvO length and charge, shape of LUMO frontier molecular orbitals), which can be theoretically calculated.

The large consumption of freshwater in fermentations and bio‐transformations is a matter of concern for the sustainability of many bio‐processes. The use of seawater to perform bio‐processes is a sustainable alternative. In this work, we used marine yeasts from deep‐sub‐seafloor sediments grown in seawater as bio‐catalysts to perform the stereoselective reduction of different ketones, and the bio‐transformations were accomplished in seawater as well. Strains of Meyerozyma guilliermondii and Rhodotorula mucilaginosa were able to reduce different aromatic ketones with high molar conversions and moderate‐to‐high enantioselectivity with no significant differences between bio‐catalysis performed in seawater and freshwater. Finally, the selected marine yeasts were used for the reduction of key intermediates in seawater for the synthesis of molecules of pharmaceutical interest (desogestrel, norgestrel, gestodene, pramipexole).