Microbial synthesis of long-chain α-alkenes from methanol by engineering Pichia pastoris

Characterization and engineering of peroxisome targeting sequences for compartmentalization engineering in Pichia pastoris

Peroxisomal compartmentalization has emerged as a highly promising strategy for reconstituting intricate metabolic pathways. In recent years, significant progress has been made in the peroxisomes through harnessing precursor pools, circumventing metabolic crosstalk, and minimizing the cytotoxicity of exogenous pathways. However, it is important to note that in methylotrophic yeasts (e.g. Pichia pastoris), the abundance and protein composition of peroxisomes are highly variable, particularly when peroxisome proliferation is induced by specific carbon sources. The intricate subcellular localization of native proteins, the variability of peroxisomal metabolic pathways, and the lack of systematic characterization of peroxisome targeting signals have limited the applications of peroxisomal compartmentalization in P. pastoris. Accordingly, this study established a high-throughput screening method based on β-carotene biosynthetic pathway to evaluate the targeting efficiency of PTS1s (Peroxisome Targeting Signal Type 1) in P. pastoris. First, 25 putative endogenous PTS1s were characterized and 3 PTS1s with high targeting efficiency were identified. Then, directed evolution of PTS1s was performed by constructing two PTS1 mutant libraries, and a total of 51 PTS1s (29 classical and 22 noncanonical PTS1s) with presumably higher peroxisomal targeting efficiency were identified, part of which were further characterized via confocal microscope. Finally, the newly identified PTS1s were employed for peroxisomal compartmentalization of the geraniol biosynthetic pathway, resulting in more than 30% increase in the titer of monoterpene compared with when the pathway was localized to the cytosol. The present study expands the synthetic biology toolkit and lays a solid foundation for peroxisomal compartmentalization in P. pastoris.

Peroxisome-based metabolic engineering for biomanufacturing and agriculture

Subcellular compartmentalization of metabolic pathways plays a crucial role in metabolic engineering. The peroxisome has emerged as a highly valuable and promising compartment for organelle engineering, particularly in the fields of biological manufacturing and agriculture. In this review, we summarize the remarkable achievements in peroxisome engineering in yeast, the industrially popular biomanufacturing chassis host, to produce various biocompounds. We also review progress in plant peroxisome engineering, a field that has already exhibited high potential in both biomanufacturing and agriculture. Moreover, we outline various experimentally validated strategies to improve the efficiency of engineered pathways in peroxisomes, as well as prospects of peroxisome engineering.

Emerging nonmodel eukaryotes for biofuel production

Microbial synthesis of biofuels offers a promising solution to the global environmental and energy concerns. However, the main challenge of microbial cell factories is their high fermentation costs. Model hosts, such as Escherichia coli and Saccharomyces cerevisiae, are typically used for proof-of-concept studies of producing different types of biofuels, however, they have a limited potential for biofuel production at an industrially relevant scale due to the weak stability/robustness and narrow substrate scope. With the advancements of synthetic biology and metabolic engineering, nonmodel eukaryotes, with naturally favorable phenotypic and metabolic features, have been emerging as promising biofuel producers. Here, we introduce the emerging nonmodel eukaryotes for the biofuel production and discuss their specific advantages, especially those with the capacity of producing cellulosic ethanol, higher alcohols, and fatty acid-/terpene-derived biofuel molecules. We also propose the challenges and prospects for developing nonmodel eukaryotic as the ideal hosts for future biofuel production.

Deciphering cell wall sensors enabling the construction of robust P. pastoris for single-cell protein production

Single-cell protein (SCP) production in the methylotrophic yeast Pichia pastoris has the potential to achieve a sustainable protein supply. However, improving the methanol fermentation efficiency and reducing carbon loss has been a long-standing challenge with far-reaching scientific and practical implications. Here, comparative transcriptomics revealed that PAS_0305, a gene directly associated with cell wall thickness under methanol stress, can be used as a target for unlocking cell wall sensors. Intracellular trehalose accumulation confirmed that cell wall sensors were activated after knocking out PAS_0305, which resulted in increased cell wall permeability. Genome-wide signal perturbations were transduced through the HOG module and the CWI pathway, which was confirmed to connected by Pbs2-Mkk. As a consequence of CWI pathway activation, ΔPAS_0305 elicited a rescue response of cell wall remodeling by increasing the β-1,3-glucan content and decreasing the chitin/mannose content. Remarkably, perturbations in global stress signals led to a fine-tuning of the metabolic network of ΔPAS_0305, resulting in a superior phenotype with highest crude protein and methanol conversion rate of 67.21% and 0.46 gDCW/g. Further genome-scale metabolic models were constructed to validate the experimental results, confirming that unlocking cell wall sensors resulted in maximized flux from methanol towards SCP and effectively addressing the issue of carbon loss in methanol fermentation. This work sheds new light on the potential of manipulating cellular signaling pathways to optimize metabolic networks and achieve exceptional phenotypic characteristics, providing new strategies for constructing versatile cell factories in P. pastoris.

Methanol-based biomanufacturing of fuels and chemicals using native and synthetic methylotrophs

Methanol has recently gained significant attention as a potential carbon substrate for the production of fuels and chemicals, owing to its high degree of reduction, abundance, and low price. Native methylotrophic yeasts and bacteria have been investigated for the production of fuels and chemicals. Alternatively, synthetic methylotrophic strains are also being developed by reconstructing methanol utilization pathways in model microorganisms, such as Escherichia coli. Owing to the complex metabolic pathways, limited availability of genetic tools, and methanol/formaldehyde toxicity, the high-level production of target products for industrial applications are still under development to satisfy commercial feasibility. This article reviews the production of biofuels and chemicals by native and synthetic methylotrophic microorganisms. It also highlights the advantages and limitations of both types of methylotrophs and provides an overview of ways to improve their efficiency for the production of fuels and chemicals from methanol.

Bioconversion of C1 feedstocks for chemical production using Pichia pastoris

Bioconversion of C1 feedstocks for chemical production offers a promising solution to global challenges such as the energy and food crises and climate change. The methylotroph Pichia pastoris is an attractive host system for the production of both recombinant proteins and chemicals from methanol. Recent studies have also demonstrated its potential for utilizing CO2 through metabolic engineering or coupling with electrocatalysis. This review focuses on the bioconversion of C1 feedstocks for chemical production using P. pastoris. Herein the challenges and feasible strategies for chemical production in P. pastoris are discussed. The potential of P. pastoris to utilize other C1 feedstocks - including CO2 and formate - is highlighted, and new insights from the perspectives of synthetic biology and material science are proposed.

Development of a Pichia pastoris cell factory for efficient production of germacrene A: a precursor of β-elemene

β-Elemene, an active ingredient found in medicinal plants like turmeric and zedoary, is a sesquiterpene compound with antitumor activity against various cancers. However, its current mode of production through plant extraction suffers from low efficiency and limited natural resources. Recently, there has been an increased interest in establishing microbial cell factories to produce germacrene A, which can be converted to β-elemene by a one-step reaction in vitro. In this study, we constructed an engineered Pichia pastoris cell factory for producing germacrene A. We rerouted the fluxes towards germacrene A biosynthesis through the optimization of the linker sequences between germacrene A synthase (GAS) and farnesyl pyrophosphate synthase (ERG20), overexpression of important pathway genes (i.e., IDI1, tHMG1, and ACS), and multi-copy integration of related expression cassettes. In combination with medium optimization and bioprocess engineering, the final titer of germacrene A in a 1 L fermenter reached 1.9 g/L through fed-batch fermentation. This represents the first report on the production of germacrene A in P. pastoris and demonstrates its advantage in producing terpenoids and other value-added natural products.

Designing Intracellular Compartments for Efficient Engineered Microbial Cell Factories

With the rapid development of synthetic biology, various kinds of microbial cell factories (MCFs) have been successfully constructed to produce high-value-added compounds. However, the complexity of metabolic regulation and pathway crosstalk always cause issues such as intermediate metabolite accumulation, byproduct generation, and metabolic burden in MCFs, resulting in low efficiencies and low yields of industrial biomanufacturing. Such issues could be solved by spatially rearranging the pathways using intracellular compartments. In this review, design strategies are summarized and discussed based on the types and characteristics of natural and artificial subcellular compartments. This review systematically presents information for the construction of efficient MCFs with intracellular compartments in terms of four aspects of design strategy goals: (1) improving local reactant concentration; (2) intercepting and isolating competing pathways; (3) providing specific reaction substances and environments; and (4) storing and accumulating products.

Engineering Komagataella phaffii to biosynthesize cordycepin from methanol which drives global metabolic alterations at the transcription level

Cordycepin has the potential to be an alternative to the disputed herbicide glyphosate. However, current laborious and time-consuming production strategies at low yields based on Cordyceps militaris lead to extremely high cost and restrict its application in the field of agriculture. In this study, Komagataella phaffii (syn. Pichia pastoris) was engineered to biosynthesize cordycepin from methanol, which could be converted from CO₂. Combined with fermentation optimization, cordycepin content in broth reached as high as 2.68 ± 0.04 g/L within 168 h, around 15.95 mg/(L·h) in productivity. Additionally, a deaminated product of cordycepin was identified at neutral or weakly alkaline starting pH during fermentation. Transcriptome analysis found the yeast producing cordycepin was experiencing severe inhibition in methanol assimilation and peroxisome biogenesis, responsible for delayed growth and decreased carbon flux to pentose phosphate pathway (PPP) which led to lack of precursor supply. Amino acid interconversion and disruption in RNA metabolism were also due to accumulation of cordycepin. The study provided a unique platform for the manufacture of cordycepin based on the emerging non-conventional yeast and gave practical strategies for further optimization of the microbial cell factory.

Production of free fatty acids from various carbon sources by Ogataea polymorpha

Energy shortage and environmental concern urgently require establishing the feasible bio-refinery process from various feedstocks. The methylotrophic yeast Ogataea polymorpha is thermo-tolerant and can utilize various carbon sources, such as glucose, xylose and methanol, which makes it a promising host for bio-manufacturing. Here, we explored the capacity of O. polymorpha for overproduction of free fatty acids (FFAs) from multiple substrates. The engineered yeast produced 674 mg/L FFA from 20 g/L glucose in shake flask and could sequentially utilize the mixture of glucose and xylose. However, the FFA producing strain failed to survive in sole methanol and supplementing co-substrate xylose promoted methanol metabolism. A synergistic utilization of xylose and methanol was observed in the FFA producing strain. Finally, a mixture of glucose, xylose and methanol was evaluated for FFA production (1.2 g/L). This study showed that O. polymorpha is an ideal host for chemical production from various carbon sources.

Establishing Komagataella phaffii as a Cell Factory for Efficient Production of Sesquiterpenoid α-Santalene

Santalene, a major component of the sandalwood essential oil, is a typical representative of sesquiterpenes and has important applications in medicine, food, flavors, and other fields. Due to the limited supply of natural sandalwood resources, there is a growing interest in engineering microbial cell factories for the mass production of santalene. In the present study, Komagataella phaffii (also known as Pichia pastoris) was established as a cell factory for high-level production of α-santalene for the first time. The metabolic fluxes were rewired toward α-santalene biosynthesis through the optimization of promoters to drive the expression of the α-santalene synthase (SAS) gene, overexpression of the key mevalonate pathway genes (i.e., tHMG1, IDI1, and ERG20), and multi-copy integration of the SAS expression cassette. In combination with medium optimization and bioprocess engineering, the optimal strain (STE-9) was able to produce α-santalene with a titer as high as 829.8 ± 70.6 mg/L, 4.4 ± 0.3 g/L, and 21.5 ± 1.6 g/L in a shake flask, batch fermenter, and fed-batch fermenter, respectively. These represented the highest production of α-santalene ever reported, highlighting the advantages of K. phaffii cell factories for the production of terpenoids and other natural products.