Improvement of natural isolates of Saccharomyces cerevisiae strains for synthesis of a chiral building block using classic genetics

Effects of the multi-stress-resistant strain Zygosaccharomyces parabailii MC-5K3 bioaugmentation on microbial communities and metabolomics in tobacco waste extract

Industrial tobacco waste was mainly treated via a reconstituted tobacco process using the paper-making method, which involves aqueous concentrated tobacco waste extract (cTWE) fermentation (aging). The fermentation was done to improve the quality of reconstituted tobacco. However, cTWE is a multi-stress environment that is characterized by low pH (about 4), as well as high sugar (above 150 g/L) and nicotine (above 15 g/L) content. In this study, a specific selection strategy was used to successfully isolate multi-stress-resistant bacterial or fungal strains, that exhibited positive effects on cTWE fermentation, thereby improving the quality of final products. A potential strain Zygosaccharomyces parabailii MC-5K3 was used for the bioaugmentation of cTWE fermentation and it significantly influenced the microbial diversity of the fermented cTWE. Zygosaccharomyces was observed to be the only dominant fungal genus instead of some pathogenic bacterial genera, with an abundance of over 95% after four days, and still more than 80% after a week. Meanwhile, metabolomics profiling showed significant concentration decrease with regard to some flavor-improving relative metabolites, such as 3-hydroxybenzoic acid (log2FC = - 5.25) and sorbitol (log2FC = - 5.54). This finding is extrapolated to be the key influence factor on the quality of the fermented cTWE. The correlation analysis also showed that the alterations in microbial diversity in the fermented cTWE led to some important differential metabolite changes, which finally improved various properties of tobacco products.

Bioproduction of 2-phenylethanol in a biphasic ionic liquid aqueous system

2-Phenylethanol (PEA) is a commercial flavor and fragrance compound, with a rose-like odor, used in the cosmetics and food industries. Saccharomyces cerevisiae strains produce PEA in a growth-associated manner but are prone to product inhibition, resulting in low production yields. The aim of this study was to use immiscible ionic liquids (ILs) in a biphasic system to enhance the PEA concentration by means of in situ product removal (ISPR). Nine ILs were tested for their influence on growing yeast cells, and five of them were found to be biocompatible. A correlation between the IL structure and the effect on yeast growth was investigated. [Tf(2)N] anions were found to be the most biocompatible in comparison to [PF(6)] and [BF(4)], and the pyridinium and ammonium cations were slightly preferable than the imidazolium cation. Furthermore, the longer the alkyl side chain on the imidazolium ring, the less it is biocompatible, with major significance above six carbons. The five biocompatible ILs were tested for PEA recovery capability by determining their distribution coefficients (K(D)), with the highest value of 17.6 obtained for BMIM[Tf(2)N]. Finally, ILs were tested for their efficiency as ISPR solvents under stress conditions of a high product concentration. A 3-5-fold increase in the total PEA concentration produced by the cells was obtained with MPPyr[Tf(2)N], OMA[Tf(2)N], and BMIM[Tf(2)N], demonstrating the potential of ILs for enhancing productivity in bioprocesses using growing cells.