Balázs Erdélyi

The vaginal microbiota plays a crucial role in bovine reproductive health in the periparturient period. This study aimed to characterize the naturally occurring bacterial species in the vaginal microbiome of healthy Holstein Frisian cows and evaluate their antibiotic sensitivity. Vaginal samples were collected from 44 healthy cows on three dairy farms. A total of 54 bacterial species were detected, with Gram-positive bacteria comprising 87% of the isolates. The most prevalent genera were Bacillus, Streptococcus, and Staphylococcus. Antibiotic susceptibility tests indicated that some isolates carried resistance genes, but most remained sensitive to commonly used antibiotics. The average vaginal mucosa pH was 7.2. These findings provide valuable insights into the diversity of vaginal microbiota of healthy dairy cows. Understanding the bacterial composition and antibiotic susceptibility can support reproductive health management and prudent use of antibiotics in dairy herds.

In this study, yeast strains were screened and immobilized in a form preserving the multifaceted biocatalytic activity. Im-mobilization of the silica-supported whole-cells of various yeasts – such as Lodderomyces elongisporus, Pichia carsonii, Candida norvegica and Debaryomyces fabryi – by sol-gel entrapment resulted in easy-to-handle biocatalysts that mediated efficiently different types of synthetic reactions. In the present study, the enantiotope selective reduction of prochiral ke-tones 1a-d and the acyloin condensation of benzaldehyde 3 were studied representing two remarkably diverse types of bio-transformation. The yeast cell biocatalysts – in the presence of fresh or recovered NADH cofactor – could be applied for continuous-flow bioreduction of ketones 1a,b with moderate to good yields (20 to 92%) and excellent enantiomeric purity (>99%). Immobilized L. elongisporus and P. carsonii cells could also mediate acyloin condensation of benzaldehyde 3 in batch as well as in continuous-flow mode. The switchable biocatalytic activity of the immobilized yeast cells was demon-strated by consecutive biotransformations under continuous-flow conditions involving reduction of phenylacetone 1a to (S)-phenylpropane-2-ol (S)-2a first, followed by conversion of benzaldehyde 3 to (R)-1-hydroxy-1-phenylpropan-2-one (R)-4 and reduction of 1a to (S)-2a again by using the same packed bed bioreactor.

Immobilization of transaminases creates promising biocatalysts for production of chiral amines in batch or continuous-flow mode reactions. E. coli cells containing overexpressed transaminases of various selectivities and hollow silica microspheres as supporting agent were immobilized by an improved sol-gel process to produce immobilized transaminase biocatalysts with suitable stability and mechanical properties for continuous-flow applications. The immobilized cell-based transaminase biocatalyst proved to be durable and easy-to-use in kinetic resolution of four racemic amines 1a–d. The batch and continuous-flow mode kinetic resolutions with transaminase biocatalyst of opposite stereopreference provided access to both enantiomers of the corresponding amines. By using the most suitable immobilized transaminase biocatalysts, this study describes the first transaminase-based approach for the production of both pure enantiomers of 1-(3,4-dimethoxyphenyl)ethan-1-amine 1d.