Crosslinked, cryostructured Lactobacillus reuteri monoliths for production of 3-hydroxypropionaldehyde, 3-hydroxypropionic acid and 1,3-propanediol from glycerol

Production of 3-Hydroxypropionic Acid from Renewable Substrates by Metabolically Engineered Microorganisms: A Review

3-Hydroxypropionic acid (3-HP) is a platform chemical with a wide range of existing and potential applications, including the production of poly(3-hydroxypropionate) (P-3HP), a biodegradable plastic. The microbial synthesis of 3-HP has attracted significant attention in recent years due to its green and sustainable properties. In this paper, we provide an overview of the microbial synthesis of 3-HP from four major aspects, including the main 3-HP biosynthesis pathways and chassis strains used for the construction of microbial cell factories, the major carbon sources used for 3-HP production, and fermentation processes. Recent advances in the biosynthesis of 3-HP and related metabolic engineering strategies are also summarized. Finally, this article provides insights into the future direction of 3-HP biosynthesis.

Biocatalytic gateway to convert glycerol into 3-hydroxypropionic acid in waste-based biorefineries: Fundamentals, limitations, and potential research strategies

Microbial conversion of bioenergy-derived waste glycerol into value-added chemicals has emerged as an important bioprocessing technology due to its eco-friendliness, feasible technoeconomics, and potential to provide sustainability in biodiesel and bioethanol production. Glycerol is an abundant liquid waste from bioenergy plants with a projected volume of 6 million tons by 2025, accounting for about 10% of biodiesel and 2.5% of bioethanol yields. 3-Hydroxypropionic acid (3-HP) is a major product of glycerol bioconversion, which is the third largest biobased platform compound with expected market size and value of 3.6 million tons/year and USD 10 billion/year, respectively. Despite these biorefinery values, 3-HP biosynthesis from glycerol is still at an immature stage of commercial exploitation. The main challenges behind this immaturity are the toxic effects of 3-HPA on cells, the distribution of carbon flux to undesirable pathways, low tolerance of cells to glycerol and 3-HP, co-factor dependence of enzymes, low enzyme activity and stability, and the problems of substrate inhibition and specificity of enzymes. To address these challenges, it is necessary to understand the fundamentals of glycerol bioconversion and 3-HP production in terms of metabolic pathways, related enzymes, cell factories, midstream process configurations, and downstream 3-HP recovery, as discussed in this review critically and comprehensively. It is equally important to know the current challenges and limitations in 3-HP production, which are discussed in detail along with recent research efforts and remaining gaps. Finally, possible research strategies are outlined considering the recent technological advances in microbial biosynthesis, aiming to attract further research efforts to achieve a sustainable and industrially exploitable 3-HP production technology. By discussing the use of advanced tools and strategies to overcome the existing challenges in 3-HP biosynthesis, this review will attract researchers from many other similar biosynthesis technologies and provide a common gateway for their further development.

Extraction, Isolation, and Purification of Value-Added Chemicals from Lignocellulosic Biomass

This review covers the operating conditions for extracting top value-added chemicals, such as levulinic acid, lactic acid, succinic acid, vanillic acid, 3-hydroxypropionic acid, xylitol, 2,5-furandicarboxylic acid, 5-hydroxymethyl furfural, chitosan, 2,3-butanediol, and xylo-oligosaccharides, from common lignocellulosic biomass. Operating principles of novel extraction methods, beyond pretreatments, such as Soxhlet extraction, ultrasound-assisted extraction, and enzymatic extraction, are also presented and reviewed. Post extraction, high-value biochemicals need to be isolated, which is achieved through a combination of one or more isolation and purification steps. The operating principles, as well as a review of isolation methods, such as membrane filtration and liquid–liquid extraction and purification using preparative chromatography, are also discussed.

Polymeric Materials Used for Immobilisation of Bacteria for the Bioremediation of Contaminants in Water

Bioremediation is a key process for reclaiming polluted soil and water by the use of biological agents. A commonly used approach aims to neutralise or remove harmful pollutants from contaminated areas using live microorganisms. Generally, immobilised microorganisms rather than planktonic cells have been used in bioremediation methods. Activated carbon, inorganic minerals (clays, metal oxides, zeolites), and agricultural waste products are acceptable substrates for the immobilisation of bacteria, although there are limitations with biomass loading and the issue with leaching of bacteria during the process. Various synthetic and natural polymers with different functional groups have been used successfully for the efficient immobilisation of microorganisms and cells. Promise has been shown using macroporous materials including cryogels with entrapped bacteria or cells in applications for water treatment and biotechnology. A cryogel is a macroporous polymeric gel formed at sub-zero temperatures through a process known as cryogelation. Macroporous hydrogels have been used to make scaffolds or supports for immobilising bacterial, viral, and other cells. The production of composite materials with immobilised cells possessing suitable mechanical and chemical stability, porosity, elasticity, and biocompatibility suggests that these materials are potential candidates for a range of applications within applied microbiology, biotechnology, and research. This review evaluates applications of macroporous cryogels as tools for the bioremediation of contaminants in wastewater.

Psychrophile-based simple biocatalysts for effective coproduction of 3-hydroxypropionic acid and 1,3-propanediol

3-Hydroxypropionic acid (3-HP) and 1,3-propanediol (1,3-PDO) have tremendous potential markets in many industries. This study evaluated the simultaneous biosynthesis of the 2 compounds using the new psychrophile-based simple biocatalyst (PSCat) reaction system. The PSCat method is based on the expression of glycerol dehydratase, 1,3-propanediol dehydrogenase, and aldehyde dehydrogenase from Klebsiella pneumoniae in Shewanella livingstonensis Ac10 and Shewanella frigidimarina DSM 12253, individually. Heat treatment at 45 °C for 15 min deactivated the intracellular metabolic flux, and the production process was started after adding substrate, cofactor, and coenzyme. In the solo production process after 1 h, the maximum production of 3-HP was 62.0 m m. For 1,3-PDO, the maximum production was 25.0 m m. In the simultaneous production process, productivity was boosted, and the production of 3-HP and 1,3-PDO increased by 13.5 and 4.9 m m, respectively. Hence, the feasibility of the individual production and the simultaneous biosynthesis system were verified in the new PSCat approach.

High-level production of 3-hydroxypropionic acid from glycerol as a sole carbon source using metabolically engineered Escherichia coli

As climate change is an important environmental issue, the conventional petrochemical-based processes to produce valuable chemicals are being shifted toward eco-friendly biological-based processes. In this study, 3-hydroxypropionic acid (3-HP), an industrially important three carbon (C3) chemical, was overproduced by metabolically engineered Escherichia coli using glycerol as a sole carbon source. As the first step to construct a glycerol-dependent 3-HP biosynthetic pathway, the dhaB1234 and gdrAB genes from Klebsiella pneumoniae encoding glycerol dehydratase and glycerol reactivase, respectively, were introduced into E. coli to convert glycerol into 3-hydroxypropionaldehyde (3-HPA). In addition, the ydcW gene from K. pneumoniae encoding γ-aminobutyraldehyde dehydrogenase, among five aldehyde dehydrogenases examined, was selected to further convert 3-HPA to 3-HP. Increasing the expression level of the ydcW gene enhanced 3-HP production titer and reduced 1,3-propanediol production. To enhance 3-HP production, fed-batch fermentation conditions were optimized by controlling dissolved oxygen (DO) level and employing different feeding strategies including intermittent feeding, pH-stat feeding, and continuous feeding strategies. Fed-batch culture of the final engineered E. coli strain with DO control and continuous feeding strategy produced 76.2 g/L of 3-HP with the yield and productivity of 0.457 g/g glycerol and 1.89 g·L^-1 ·h^-1 , respectively. To the best of our knowledge, this is the highest 3-HP productivity achieved by any microorganism reported to date.

Improved production of 3-hydroxypropionic acid in engineered Escherichia coli by rebalancing heterologous and endogenous synthetic pathways

To improve 3-hydroxypropionic acid (3-HP) production by Escherichia coli, glycerol accumulation needs to be reduced. To accomplish this, we constructed a novel E. coli strain that overexpresses the endogenous aldehyde dehydrogenase gene (puuC) under the control of a strong promoter. The fermentation performance of the engineered strain was significantly improved compared to that of the parental control strain in the presence of glucose and xylose. We also inactivated the puu operon repressor gene, puuR, which resulted in a decrease in glycerol accumulation and an increase in 3-HP production through the co-fermentation of glucose and xylose. Through fed-batch fermentation by utilizing glucose and xylose, the engineered strain, JHS_Δgypr-PT7, produced 53.7 g/L 3-HP and accumulated 1.5 g/L glycerol. This combination strategy, wherein we overexpressed the endogenous puuC gene from a strong promoter and eliminate its transcriptional repression, may be extended to rebalance another biochemical pathway.

Enhanced production of 3-hydroxypropionic acid from glucose and xylose by alleviation of metabolic congestion due to glycerol flux in engineered Escherichia coli

Among platform chemicals obtained from renewable biomass, 3-hydroxypropionic acid (3-HP) has attracted considerable attention. A GC/TOF-MS study revealed that the intracellular metabolites of the TCA cycle and fatty acid synthesis increased in JHS01302, a galP-overexpressing strain of Escherichia coli, during glucose and xylose co-fermentation. Decreased intracellular glycerol levels and increased intracellular biosynthesis of 3-HP were also detected in the strain. Based on these results, the yeast GPD1 gene was replaced with the endogenous gpsA gene to modulate the rate of glycerol metabolism. In flask cultures, JHS01304 containing the gpsA gene displayed 43% lower glycerol accumulation and 52% higher 3-HP production than the control. JHS01304 produced 37.6 g/L 3-HP with a productivity rate of 0.63 g/L/h and yield of 0.17 g/g in the fed-batch fermentation. The metabolome analysis provided valuable information for alleviating the metabolic burden of glycerol flux to improve the production of 3-HP during glucose and xylose co-fermentation.

Enhancing 3-hydroxypropionic acid production in combination with sugar supply engineering by cell surface-display and metabolic engineering of Schizosaccharomyces pombe

Background

Economical production of value-added chemicals from renewable biomass is a promising path to sustainability. 3-Hydroxypropionic acid (3-HP) is an important chemical for building a bio-sustainable society. Establishment of 3-HP production from renewable resources such as glucose would provide a bio-sustainable alternative to the production of acrylic acid from fossil resources.

Results

Here, we describe metabolic engineering of the fission yeast Schizosaccharomyces pombe to enhance 3-HP production from glucose and cellobiose via the malonyl-CoA pathway. The mcr gene, encoding the malonyl-CoA reductase of Chloroflexus aurantiacus, was dissected into two functionally distinct fragments, and the activities of the encoded protein were balanced. To increase the cellular supply of malonyl-CoA and acetyl-CoA, we introduced genes encoding endogenous aldehyde dehydrogenase, acetyl-CoA synthase from Salmonella enterica, and endogenous pantothenate kinase. The resulting strain produced 3-HP at 1.0 g/L from a culture starting at a glucose concentration of 50 g/L. We also engineered the sugar supply by displaying beta-glucosidase (BGL) on the yeast cell surface. When grown on 50 g/L cellobiose, the beta-glucosidase-displaying strain consumed cellobiose efficiently and produced 3-HP at 3.5 g/L. Under fed-batch conditions starting from cellobiose, this strain produced 3-HP at up to 11.4 g/L, corresponding to a yield of 11.2% (g-3-HP/g-glucose; given that 1 g cellobiose corresponds to 1.1 g glucose upon digestion).

Conclusions

In this study, we constructed a series of S. pombe strains that produced 3-HP via the malonyl-CoA pathway. Our study also demonstrated that BGL display using cellobiose and/or cello-oligosaccharides as a carbon source has the potential to improve the titer and yield of malonyl-CoA- and acetyl-CoA-derived compounds.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-1025-5) contains supplementary material, which is available to authorized users.

One-step formation of three-dimensional macroporous bacterial sponges as a novel approach for the preparation of bioreactors for bioremediation and green treatment of water

A novel method of crosslinking live bacteria into a stable 3D porous structure and its subsequent use in phenol degradation is reported.