A novel CRISPR/Cas9 system with high genomic editing efficiency and recyclable auxotrophic selective marker for multiple-step metabolic rewriting in Pichia pastoris

CRISPR-Cas9-based one-step multiplexed genome editing through optimizing guide RNA processing strategies in Pichia pastoris

The important methylotrophic yeast Pichia pastoris has been utilized for the production of a variety of heterologous recombinant proteins and has great potential for use in the production of value-added compounds using methanol as a substrate. However, the lack of convenient and efficient genome engineering tools has hindered further applications of P. pastoris, especially in complex and multistep metabolic engineering scenarios. Hence, we developed a rapid and convenient multi-gene editing system based on CRISPR/Cas9 by optimizing the guide RNA processing strategy, which can achieve dual-gene knockout or multi-gene integration in single step. Firstly, we found that the HgH (HH-sgRNA-HDV) structure achieved the highest single-gene knockout efficiency (95.8 %) among the three sgRNA processing cassettes, including a tRNA-sgRNA-tRNA (tgt) array, HgH structure and tRNA-sgRNA-HDV (tgH) structure. Furthermore, the dHgH structure (double HgH) enabled one-step dual-gene disruption and multi-gene integration. The efficiency of dual-site knockout ranged from 60 % to 100 %, with functional genes knockout achieving approximately 60 % (Δaox1Δgut1), while dual neutral sites knockout reached 100 %. Finally, we applied the system for one-step production of fatty acids and 5-hydroxytryptophan. The yield of FFAs reached 23 mg/L/μg protein/OD, while the yield of 5-hydroxytryptophan was 13.3 mg/L. The system will contribute to the application of P. pastoris as an attractive cell factory for multiplexed compound biosynthesis and will serve as a valuable tool for enhancing one-carbon (C1) bio-utilization.

Metabolic engineering for sustainable xylitol production from diverse carbon sources in Pichia pastoris

Xylitol, known for its health benefits, is a valuable compound in the food and pharmaceutical industries. However, conventional chemical production methods are often unsustainable for large-scale applications, prompting the need for alternative approaches. This study demonstrates a significant enhancement in xylitol production using microbial cell factories, optimized through metabolic engineering. Two synthetic pathways were combined, and the introduction of a novel NADPH-dependent xylitol dehydrogenase further boosted xylitol yields, achieving 0.14 g xylitol/g glucose-a record-high yield for microbial systems. Additionally, the use of sustainable feedstocks, such as glycerol and methanol, led to the production of 7000 mg/L xylitol with a yield of 0.35 g xylitol/g glycerol, and 250 mg/L xylitol from methanol. These results underscore the potential for eco-friendly, cost-effective xylitol production, providing a robust foundation for future industrial-scale biotechnological applications.

Advancing recombinant protein expression in Komagataella phaffii: opportunities and challenges

Komagataella phaffii has gained recognition as a versatile platform for recombinant protein production, with applications covering biopharmaceuticals, industrial enzymes, food additives, etc. Its advantages include high-level protein expression, moderate post-translational modifications, high-density cultivation, and cost-effective methanol utilization. Nevertheless, it still faces challenges for the improvement of production efficiency and extension of applicability. This review highlights the key strategies used to facilitate productivity in K. phaffii, including systematic advances in genetic manipulation tools, transcriptional and translational regulation, protein folding and secretion optimization. Glycosylation engineering is also concerned as it enables humanized glycosylation profiles for the use in therapeutic proteins and functional food additivities. Omics technologies and genome-scale metabolic models provide new insights into cellular metabolism, enhancing recombinant protein expression. High-throughput screening technologies are also emphasized as crucial for constructing high-expression strains and accelerating strain optimization. With advancements in gene-editing, synthetic and systems biology tools, the K. phaffii expression platform has been significantly improved for fundamental research and industrial use. Future innovations aim to fully harness K. phaffii as a next-generation cell factory, providing efficient, scalable, and cost-effective solutions for diverse applications. It continues to hold promise as a key driver in the field of biotechnology.

Komagataella phaffii as a Platform for Heterologous Expression of Enzymes Used for Industry

In the 1980s, Escherichia coli was the preferred host for heterologous protein expression owing to its capacity for rapid growth in complex media; well-studied genetics; rapid and direct transformation with foreign DNA; and easily scalable fermentation. Despite the relative ease of use of E. coli for achieving the high expression of many recombinant proteins, for some proteins, e.g., membrane proteins or proteins of eukaryotic origin, this approach can be rather ineffective. Another microorganism long-used and popular as an expression system is baker's yeast, Saccharomyces cerevisiae. In spite of a number of obvious advantages of these yeasts as host cells, there are some limitations on their use as expression systems, for example, inefficient secretion, misfolding, hyperglycosylation, and aberrant proteolytic processing of proteins. Over the past decade, nontraditional yeast species have been adapted to the role of alternative hosts for the production of recombinant proteins, e.g., Komagataella phaffii, Yarrowia lipolytica, and Schizosaccharomyces pombe. These yeast species' several physiological characteristics (that are different from those of S. cerevisiae), such as faster growth on cheap carbon sources and higher secretion capacity, make them practical alternative hosts for biotechnological purposes. Currently, the K. phaffii-based expression system is one of the most popular for the production of heterologous proteins. Along with the low secretion of endogenous proteins, K. phaffii efficiently produces and secretes heterologous proteins in high yields, thereby reducing the cost of purifying the latter. This review will discuss practical approaches and technological solutions for the efficient expression of recombinant proteins in K. phaffii, mainly based on the example of enzymes used for the feed industry.

Oligonucleotide-based CRISPR-Cas9 toolbox for efficient engineering of Komagataella phaffii

Komagataella phaffii (Pichia pastoris) is a methylotrophic yeast that is favored by industry and academia mainly for expression of heterologous proteins. However, its full potential as a host for bioproduction of valuable compounds cannot be fully exploited as genetic tools are lagging behind those that are available for baker's yeast. The emergence of CRISPR-Cas9 technology has significantly improved the efficiency of gene manipulations of K. phaffii, but improvements in gene-editing methods are desirable to further accelerate engineering of this yeast. In this study, we have developed a versatile vector-based CRISPR-Cas9 method and showed that it works efficiently at different genetic loci using linear DNA fragments with very short targeting sequences including single-stranded oligonucleotides. Notably, we performed site-specific point mutations and full gene deletions using short (90 nt) single-stranded oligonucleotides at very high efficiencies. Lastly, we present a strategy for transient inactivation of nonhomologous end-joining (NHEJ) pathway, where KU70 gene is disrupted by a visual marker (uidA gene). This system enables precise CRISPR-Cas9-based editing (including multiplexing) and facilitates simple reversion to NHEJ-proficient genotype. In conclusion, the tools presented in this study can be applied for easy and efficient engineering of K. phaffii strains and are compatible with high-throughput automated workflows.

Heterologous Single-Strand DNA-Annealing and Binding Protein Enhance CRISPR-Based Genome Editing Efficiency in Komagataella phaffii

The industrial yeast Komagataella phaffii is a highly effective platform for heterologous protein production, owing to its high protein expression and secretion capacity. Heterologous genes and proteins are involved in multiple processes, including transcription, translation, protein folding, modification, transportation, and degradation; however, engineering these proteins and genes is challenging due to inefficient genome editing techniques. We employed Pseudomonas aeruginosa phage single-stranded DNA-annealing protein (SSAP) PapRecT and P. aeruginosa single-stranded DNA-binding protein (SSB) PaSSB to introduce SSAP-SSB-based homology recombination, which facilitated K. phaffii CRISPR-based genome engineering. Specifically, a host-independent method was developed by expressing sgRNA with PapRecT-PaSSB in a single plasmid, with which only a 50 bp short homologous arm (HA) reached a 100% positive rate for CRISPR-based gene insertion, reaching 18 colony-forming units (CFU) per μg of donor DNA. Single deletion using 1000 bp HA attained 100%, reaching 68 CFUs per μg of donor DNA. Using this efficient CRISPR-based genome editing tool, we integrated three genes (INO4, GAL4-like, and PAB1) at three different loci for overexpression to realize the collaborative regulation of human-lactalbumin (α-LA) production. Specifically, we strengthened phospholipid biosynthesis to facilitate endoplasmic reticulum membrane formation and enhanced recombinant protein transcription and translation by overexpressing transcription and translation factors. The final production of α-LA in the 3 L fermentation reached 113.4 mg L-1, two times higher than that of the strain without multiple site gene editing, which is the highest reported titer in K. phaffii. The CRISPR-based genome editing method developed in this study is suitable for the synergistic multiple-site engineering of protein and biochemical biosynthesis pathways to improve the biomanufacturing efficiency.