Background: Two important flavonoids, kaempferol and quercetin possess remarkably potent biological impacts on human health. However, their structural complexity and low abundance in nature make both bulk chemical synthesis and extraction from native plants difficult. Therefore microbial production via heterologous expression of plant enzymes can be a safe and sustainable route for their production. Despite several attempts reported in microbial hosts, the production levels of kaempferol and quercetin still stay far behind compared to many other microbial-produced flavonoids. Results: In this study, Saccharomyces cerevisiae was engineered for high production of kaempferol and quercetin in minimal media from glucose. First, the kaempferol biosynthetic pathway was reconstructed via screening various F3H and FLS enzymes. In addition, we demonstrated that amplification of the rate-limiting enzyme AtFLS could reduce the dihydrokaempferol accumulation and improve kaempferol production. Increasing the availability of precursor malonyl-CoA further improved the production of kaempferol and quercetin. Furthermore, the highest amount of 956 mg L^− 1 of kaempferol and 930 mg L^− 1 of quercetin in yeast was reached in fed-batch fermentations. Conclusions: De novo biosynthesis of kaempferol and quercetin in yeast was improved through increasing the upstream naringenin biosynthesis and debugging the flux-limiting enzymes together with fed-batch fermentations, up to gram per liter level. Our work provides a promising platform for sustainable and scalable production of kaempferol, quercetin and compounds derived thereof.

Saccharomyces cerevisiae is widely adopted as a chassis in synthetic biology. However, heterologous constructs often disrupt proteostasis, metabolism, redox balance, and secretory processes. These disruptions activate a complex network of stress pathways. These include the heat shock response, unfolded protein response, oxidative stress defenses, cell wall integrity signaling, the high-osmolarity glycerol pathway, and Snf1/AMPK-mediated energy regulation. Collectively, these pathways form a stressome that maintains cellular homeostasis but constrains productive capacity. A comprehensive understanding of how synthetic designs interact with these pathways is essential for developing robust yeast systems. Strategies such as promoter tuning, chaperone augmentation, redox and cofactor balancing, lipid and membrane optimization, dynamic regulation, and pathway compartmentalization can reduce cellular burden. Emerging methods also improve stress mitigation. These include CRISPR-based circuit rewiring, adaptive laboratory evolution, synthetic organelle construction, and data-driven strain engineering. This review summarizes construct-induced stress in engineered yeast and presents stress-aware design principles to advance more resilient, higher-yielding S. cerevisiae strains for biotechnology.

Although genetic material is vertically transferred between generations via sexual or asexual reproduction, similarities in some chromosome and gene parts of unrelated organisms provide important clues for another way of transfer. The mobility of genetic information among different organisms, known as horizontal gene transfer (HGT) has immediate or delayed effects on the recipient host. One of the most notable mechanisms of HGT is natural transformation (NT), a process in which cells take free DNA from the extracellular environment and incorporate it into their chromosomes by homologous recombination. NT is widely conserved in many bacterial species as it can promote to spread of resistance genes. Although it is known that many organisms rely on HGT, there is limited information about how they decide which particular genetic material to horizontally transfer. Here, I have investigated the preference priority among different gene sources presented under certain stress conditions for Bacillus subtilis possessing NT ability. To test this, two DNA specimens (E and C) with different sequence contents of the same length were presented to B. subtilis under different stress environments (BK, BC, BE and BCE). The hypothesis was evaluated according to the analysis of the results of colonial formations on selective plates (pE, pC and pCE). The obtained data presented a strong positive correlation that the bacteria have preference priority during NT depending on a stimulator. The tendency of the bacteria to uptake useful DNA fragments in a specific environment can be suggested. For instance, the majority of colonies grow on pE plates rather than the pC and pCE when the transformation media includes erythromycin (Eryt) as an inducer. Although the data significantly overlaps with the idea claiming that the bacteria have a preference priority to uptake free DNAs during NT, further investigations are needed to support the present data and for better understanding of the phenomenon.

Resistance to nucleoside-like compounds in cancer treatment is a significant problem. However, the transcriptional pathways by which cancer cells adapt und