Genomic and metabolic instability during long-term fermentation of an industrial Saccharomyces cerevisiae strain engineered for C5 sugar utilization

Beyond CEN.PK - parallel engineering of selected S. cerevisiae strains reveals that superior chassis strains require different engineering approaches for limonene production

Genetically engineered microbes are increasingly utilized to produce a broad range of high-value compounds. However, most studies start with only a very narrow group of genetically tractable type strains that have not been selected for maximum titers or industrial robustness. In this study, we used high-throughput screening and parallel metabolic engineering to identify and optimize Saccharomyces cerevisiae chassis strains for the production of limonene, a monoterpene with applications in flavors, fragrances, and biofuels. We screened 921 genetically and phenotypically distinct S. cerevisiae strains for limonene tolerance and lipid content to identify optimal chassis strains for precision fermentation of limonene. In parallel, we also evaluated 16 different plant limonene synthases. Our results revealed that two of the selected strains showed approximately a 2-fold increase in titers compared to CEN.PK2-1C, the type strain that is often used as a chassis for limonene production, with the same genetic modifications in the mevalonate pathway. Intriguingly, the most effective engineering strategy proved strain-specific. Metabolic profiling revealed that this difference is likely explained by differences in native mevalonate production. Ultimately, by using strain-specific engineering strategies, we achieved 844 mg/L in a new strain, 40 % higher than the titer (605 mg/L) achieved by CEN.PK2-1C. Our findings demonstrate the potential of leveraging genetic diversity in S. cerevisiae for monoterpene bioproduction and highlight the necessity for tailoring metabolic engineering strategies to specific strains.

Transferability of bioprocessing modes for recombinant protease production: from fed-batch to continuous cultivation with Bacillus licheniformis

BACKGROUND

Proteases are essential in various industries due to their unique substrate specificities and robustness in different operational conditions. Bacillus strains consist of a genotype favorable for rapid growth whilst secreting enzymes extracellularly, thereby simplifying recombinant protease production. Despite the widespread use of batch and fed-batch fermentations for their ease and robustness, these cultivation types are often marred by significant energy requirements and prolonged downtimes. The switch towards continuous cultivation methods promises reduced carbon footprints and improved equipment efficiency. Yet, research focusing on Bacillus strains is limited, therefore we aimed to establish a continuous cultivation as a competitive alternative to fed-batch.

RESULTS

Therefore, this study aimed to explore the potential of chemostat cultivations for producing a protease from Bacillus licheniformis utilizing a derepressed induction system, and comparing specific productivities and space-time yields to fed-batch cultivations. The continuous cultivations were described in a hybrid model, considering the effect of productivity as function of the applied dilution rate as well as the generation time. The workflow of this study demonstrates that screenings in a fed-batch mode and chemostat cultivations conducted at the same growth rate, result in different specific productivities for derepressible systems.

CONCLUSION

The results of this study highlight that the feeding rate's impact on specific productivity varies significantly between fed-batch and chemostat cultivations. These differences suggest that fed-batch screenings may not be adequate for developing a continuous process using a derepressed promoter system in B. licheniformis. Although the space-time yield of fed-batch cultivations has not been surpassed by stable continuous operations-achieving only a third of the highest space-time yield observed in fed-batch-valuable mechanistic insights have been gained. This knowledge could facilitate the transition towards a more sustainable mode of cultivation for industrial protease production.

Unforeseen current and future benefits of uncommon yeast: the Metschnikowia genus

Metschnikowia, the single-cell yeast form, is a genus of 85 species in the Saccharomycetales order that developed in both aquatic and terrestrial ecosystems after being found in 1899. This yeast is commonly used to control microbial populations in many biological and artificial conditions, such as fermentation. However, current study of Metschnikowia is limited to biological control features rather than researching on lucrative sectors such as beverage production, bioconversion manufacturing, cosmetics, and the pharmaceutical industry. This review summarizes numerous possible applications of Metschnikowia in human life, including potential secondary metabolites in industrial fields such as cosmetics and pharmaceuticals. Furthermore, Metschnikowia-yeast interaction is mentioned as a potential area for further exploration in terms of co-cultured microbes as biocontrol. Since Metschnikowia yeast arose in a variety of ecosystems, more discussion will be held regarding the interactions between Metschnikowia and their surroundings, particularly in fruits. Finally, the current regulatory challenges of Metschnikowia-based products are examined, and future research opportunities on Metschnikowia utilization are presented. KEY POINTS: • Utilization of Metschnikowia genus in various human aspects. • Promising secondary metabolites produced by Metschnikowia. • Challenge and opportunity on developing Metschnikowia-based products.