Impact of the Whole Genome Duplication Event on PYK Activity and Effects of a PYK1 Mutation on Metabolism in S. cerevisiae

The advances in creating Crabtree-negative Saccharomyces cerevisiae and the application for chemicals biosynthesis

Saccharomyces cerevisiae is a promising microbial cell factory. However, the overflow metabolism, known as the Crabtree effect, directs the majority of the carbon source toward ethanol production, in many cases, resulting in low yields of other target chemicals and byproducts accumulation. To construct Crabtree-negative S. cerevisiae, the deletion of pyruvate decarboxylases and/or ethanol dehydrogenases is required. However, these modifications compromises the growth of the strains on glucose. This review discusses the metabolic engineering approaches used to eliminate ethanol production, the efforts to alleviate growth defect of Crabtree-negative strains, and the underlying mechanisms of the growth rescue. In addition, it summarizes the applications of Crabtree-negative S. cerevisiae in the synthesis of various chemicals such as lactic acid, 2,3-butanediol, malic acid, succinic acid, isobutanol, and others.

Intake of compound probiotics accelerates the construction of immune function and gut microbiome in Holstein calves

Acquired immunity is an important way to construct the intestinal immune barrier in mammals, which is almost dependent on suckling. To develop a new strategy for accelerating the construction of gut microbiome, newborn Holstein calves were continuously fed with 40 mL of compound probiotics (containing Lactobacillus plantarum T-14, Enterococcus faecium T-11, Saccharomyces cerevisiae T-209, and Bacillus licheniformis T-231) per day for 60 days. Through diarrhea rate monitoring, immune index testing, antioxidant capacity detection, and metagenome sequencing, the changes in diarrhea incidence, average daily gain, immune index, and gut microbiome of newborn calves within 60 days were investigated. Results indicated that feeding the compound probiotics reduced the average diarrhea rate of calves by 42.90%, increased the average daily gain by 43.40%, raised the antioxidant indexes of catalase, superoxide dismutase, total antioxidant capacity, and Glutathione peroxidase by 22.81%, 6.49%, 8.33%, and 13.67%, respectively, and increased the immune indexes of IgA, IgG, and IgM by 10.44%, 4.85%, and 6.12%, respectively. Moreover, metagenome sequencing data showed that feeding the compound probiotics increased the abundance of beneficial strains (e.g., Lactococcus lactis and Bacillus massionigeriensis) and decreased the abundance of some harmful strains (e.g., Escherichia sp. MOD1-EC5189 and Mycobacterium brisbane) in the gut microbiome of calves, thus contributing to accelerating the construction of healthy gut microbiome in newborn Holstein calves.

IMPORTANCE

The unstable gut microbiome and incomplete intestinal function of newborn calves are important factors for the high incidence of early diarrhea. This study presents an effective strategy to improve the overall immunity and gut microbiome in calves and provides new insights into the application of compound probiotics in mammals.

Adaptations in metabolism and protein translation give rise to the Crabtree effect in yeast

Aerobic fermentation, also referred to as the Crabtree effect in yeast, is a well-studied phenomenon that allows many eukaryal cells to attain higher growth rates at high glucose availability. Not all yeasts exhibit the Crabtree effect, and it is not known why Crabtree-negative yeasts can grow at rates comparable to Crabtree-positive yeasts. Here, we quantitatively compared two Crabtree-positive yeasts, Saccharomyces cerevisiae and Schizosaccharomyces pombe, and two Crabtree-negative yeasts, Kluyveromyces marxianus and Scheffersomyces stipitis, cultivated under glucose excess conditions. Combining physiological and proteome quantification with genome-scale metabolic modeling, we found that the two groups differ in energy metabolism and translation efficiency. In Crabtree-positive yeasts, the central carbon metabolism flux and proteome allocation favor a glucose utilization strategy minimizing proteome cost as proteins translation parameters, including ribosomal content and/or efficiency, are lower. Crabtree-negative yeasts, however, use a strategy of maximizing ATP yield, accompanied by higher protein translation parameters. Our analyses provide insight into the underlying reasons for the Crabtree effect, demonstrating a coupling to adaptations in both metabolism and protein translation.