Improved production of adipic acid from a high loading of corn stover via an efficient and mild combination pretreatment

Engineering strategies for producing medium-long chain dicarboxylic acids in oleaginous yeasts

Medium-long chain dicarboxylic acids (DCAs, C ≥ 6) are essential chemical raw materials, with wide applications in the chemical, pharmaceutical, material and food industries. However, the traditional chemical synthesis methods cause environmental pollution and are not in line with goals of sustainable development. With the development of synthetic biology, high-value-added DCAs can be biosynthesized from hydrophobic substrates (HSs) using suitable microorganisms. This review first summarizes the biosynthetic pathway of DCAs in oleaginous yeasts and then emphasizes the related engineering strategies for increasing the product yield, including promoter, enzyme, pathway, cell, fermentation, and downstream engineering. In addition, the challenges and development trends in the biosynthesis of DCAs are discussed, in light of the current progress, challenges, and trends in this field. Finally, guidelines for future research are proposed. Overall, this review systematically summarizes recent engineering strategies for DCAs production in oleaginous yeasts and offers valuable insights for future DCAs biosynthesis.

Converting a D-/L lactic acid bacteria to its d-type counterpart via a combined chemical mutagenesis and biosensor screening method, and its application in lignocellulosic biorefinery

Optically pure lactic acid is essential for poly(lactic acid) manufacturing, nonetheless, most wild-type lactic acid bacteria inherently produce D-/L- mixed lactic acid. In this study, an elaborate system was designed for developing d-lactic acid producing mutants from a wild-type D-/L- lactic acid producingLactobacillus by combining chemical mutagenesis with ethyl methane sulfonate as the mutagen and high throughput screening with a l-lactate dehydrogenase based biosensor. Mechanistic analysis revealed that the loss of l-lactate dehydrogenase activity via C → T transitions in the corresponding gene is responsible for generation of d-lactic acid producing mutants. The obtained d-lactic acid producing mutant exhibited excellent performance in different types of lignocellulosic hydrolysates and produced 128.3 g/L d-lactic acid from corn stover hydrolysate in 3-L bioreactor fermentation, with optical purity higher than 98 %. In conclusion, this study provided a practical framework for obtaining optically pure lactic acid producers without genetic engineering operations, advancing the sustainable production of cellulosic bioplastics.

Engineering Precursor and Cofactor Metabolism in Escherichia Coli for Enhanced Adipic Acid Production From Glucose

The reverse adipate degradation pathway (RADP) for adipic acid synthesis has garnered significant interest. However, the limited efficiency of existing pathways and their dependence on plasmids have hindered the practical application of microbial cell factories. In this study, the efficiency of the adipic acid synthetic pathway was enhanced by substituting and combinatorially expressing RADP enzymes. To obviate the need for chemical inducers and antibiotics, we integrated the reconstructed pathway genes into the genome of a succinic acid-producing strain Escherichia coli FMME N-26 and increased the copy number of rate-limiting enzymes. The supply of two critical precursors for adipic acid synthesis, acetyl-CoA and succinyl-CoA, was enhanced by deleting tdcD and overexpressing cat1. Additionally, cofactor metabolism was balanced through the overexpression of the udhA and dppD genes. Following these modifications, the adipic acid fermentation process was optimized in a 5 L bioreactor, resulting in a titer of 4.97 g/L after 72 h of fed-batch fermentation. This study lays a theoretical foundation and provides a technical basis for constructing cell factories to produce adipic acid and other dicarboxylic acids.

Recent Advances in the Biosynthesis of Mid- and Long-Chain Dicarboxylic Acids Using Terminally Oxidizing Unconventional Yeasts

As high-performance monomers for the manufacture of polyamide materials, mid- and long-chain dicarboxylic acids (DCAi, i ≥ 6) have received extensive attention from researchers. Biosynthesis is gradually replacing chemical synthesis due to its outstanding advantages in the industrial production of mid- and long-chain dicarboxylic acids, which is mostly achieved by using the strong terminal oxidation ability of nonmodel microorganisms such as Candida tropicalis to oxidize hydrophobic substrates such as alkanes. Here, we first summarize the metabolic pathways of oxidative alkane conversion into dicarboxylic acid by terminally oxidizing unconventional yeasts and the corresponding metabolic engineering strategies. Then, we summarize the research progress on new dicarboxylic acid production processes. Finally, the future development directions in the biosynthesis of mid- and long-chain dicarboxylic acids are prospected from synthetic biology and bioprocess engineering, which can also provide a reference for the synthesis of other biobased chemicals and biomaterials.

Improving saccharification efficiency of corn stover through ferric chloride-deep eutectic solvent pretreatment

An effective deep eutectic solvent (DES) and Iron(III) chloride (FeCl3) combination pretreatment system was developed to improve the removal efficiency of lignin and hemicellulose from corn stover (CS) and enhance its saccharification. N-(2-hydroxyethyl)ethylenediamine (NE) was selected as the hydrogen-bond-donor for preparing ChCl-based DES (ChCl:NE), and a mixture of ChCl:NE (60 wt%) and FeCl3 (0.5 wt%) was utilized for combination pretreatment of CS at 110 ℃ for 50 min. FeCl3/ChCl:NE effectively removed lignin (87.0 %) and xylan (55.9 %) and the enzymatic hydrolysis activity of FeCl3/ChCl:NE-treated CS was 5.5 times that of CS. The reducing sugar yield of pretreated CS was 98.6 %. FeCl3/ChCl:NE significantly disrupted the crystal structure of cellulose in CS and improved the removal of lignin and hemicellulose, enhancing the conversion of cellulose and hemicellulose into monomeric sugars. Overall, this combination of FeCl3 and DES pretreatment methods has high application potential for the biological refining of lignocellulose.

In situ retention of lignin-rich bamboo green effectively improves the surface properties of flattened bamboo

Bamboo has tremendous carbon sequestration potential, and bamboo green is underutilized. This work devised a green-keeping technique in bamboo flattening that preserved natural bamboo green in-situ. The impacts of flattening and green-keeping on bamboo morphology, chemical composition, physical qualities, and composite applications were examined. Bamboo cells were wrinkled after flattening, while bamboo green exhibited a more homogenous surface. Bamboo cellulose crystallinity increased after flattening, hemicellulose deteriorated little, and relative lignin content increased. The hydrophobicity and mildew resistance of the surface of G-FB (green-kept flattened bamboo board) were improved. Compared to untreated bamboo, FB and G-FB had 61.1 % and 49.5 % higher tensile strength and 8.0 % and 33.2 % higher MOR. G-FB-made flooring exhibited a MOR of 134.7 MPa and upgraded surface properties. Bamboo green preservation boosted utilization of materials and improved flattened bamboo's exterior surface without affecting lamination bonding. Simple bamboo green preservation multifunctionalizes flattened bamboo composites.

Dynamic regulation and cofactor engineering of escherichia coli to enhance production of glycolate from corn stover hydrolysate

Glycolic acid is widely employed in chemical cleaning, the production of polyglycolic acid-lactic acid, and polyglycolic acid. Currently, the bottleneck of glycolate biosynthesis lies on the imbalance of metabolic flux and the deficiency of NADPH. In this study, a dynamic regulation system was developed and optimized to enhance the metabolic flux from glucose to glycolate. Additionally, the knockout of transhydrogenase (sthA), along with the overexpression of pyridine nucleotide transhydrogenase (pntAB) and the implementation of the Entner-Doudoroff pathway, were performed to further increase the production of the NADPH, thereby increasing the titer of glycolate to 5.6 g/L. To produce glycolate from corn stover hydrolysate, carbon catabolite repression was alleviated and glucose utilization was accelerated. The final strain, E. coli Mgly10-245, is inducer-free, achieving a glycolate titer of 46.1 g/L using corn stover hydrolysate (77.1 % of theoretical yield). These findings will contribute to the advancement of industrial glycolate production.

Engineering of Yarrowia lipolytica as a platform strain for producing adipic acid from renewable resource

There is an increasing demand for bio-based dicarboxylic acids (DCA) as an eco-friendly alternatives to chemically synthesized DCA. Adipic acid, which is not naturally produced by microorganisms, is an essential DCA with significant industrial importance. This study aimed to develop a platform strain using Yarrowia lipolytica for efficient bioconversion of renewable resources into adipic acid. To prevent the complete oxidation of adipic acid, peroxisomal β-oxidation was engineered by selectively disrupting acyl-CoA oxidases. Furthermore, ω-oxidation activity was improved via introducing an additional copy of cytochrome P450 monooxygenase (ALK5) and reductase (CPR1) with fatty alcohol oxidase (FAO1). The production phase used SP92D medium in a two-stage bioconversion process, during which the engineered strain exhibited the highest production level, achieving a remarkable 9.7-fold increase compared to that of the parental strain. To our knowledge, this is the first report demonstrating that engineered Y. lipolytica can produce adipic acid from fatty acid methyl esters.

Efficient co-production of reducing sugars and xylooligosaccharides via clean hydrothermal pretreatment of rape straw

Hydrothermal treatment was applied to pretreat rape straw for the efficient co-production of reducing sugars and xylooligosaccharides. It was observed that hydrothermal treatment using water as solvent and catalyst destructed the compact structure of rape straw and increased its enzymatic digestion efficiency from 24.6% to 92.0%. Xylooligosaccharide (3.3 g/L) was acquired after the treatment under 200 °C for 60 min (severity factor Log Ro = 4.7). With increasing pretreatment intensity from 3.1 to 5.4, the hemicellulose removal increased from 14.4% to 100%, and the delignification was raised from 12% to 44%. Various characterization proved that the surface morphology of treated material showed a porous shape, while the cellulose accessibility, lignin surface area and lignin hydrophobicity were greatly improved. Consequently, hydrothermal pretreatment played a vital role in the sustainable transformation of biomass to valuable biobased compounds, and had a wide range of application prospects in lignocellulosic biorefining.

Efficient co-production of xylooligosaccharides, furfural and reducing sugars from yellow bamboo via the pretreatment with biochar-based catalyst

The research on the efficient use of biomass to produce chemical products has received extensive attention. In this work, a novel heterogeneous biocarbon-based heterogeneous catalyst AT-Sn-YB was prepared using yellow bamboo (YB) as a carrier, and its physical properties were proved to be good by various characterization and stability experiments. In the γ-valerolactone/water (3:1, v/v) medium containing 100 mM CuCl2, the use of AT-Sn-YB (3.6 wt%) under 170 °C for 20 min was applied to catalyze YB into furfural (80.3% yield), accompanied with 2.8 g/L xylooligosaccharides. The YB solid residue obtained from treatment was efficiently saccharified to reducing sugars (17.2 g/L). Accordingly, comprehensive understanding of efficiently co-producing xylooligosaccharides, furfural and reducing sugars from YB was demonstrated via the pretreatment with biochar-based catalyst. This study innovatively used a new type of solid acid to complete the efficient co-production of chemical products, and realized the value-added utilization of yellow bamboo.

Comprehensive understanding of enzymatic saccharification of Betaine:Lactic acid-pretreated sugarcane bagasse

Green solvents, especially deep eutectic solvents (DESs), are widely applied to pretreat biomass for enhancing its enzymatic hydrolysis. In this work, lactic acid was selected as the hydrogen-bond-donor to prepare Betaine-base DES (Betaine:LA), The DES was utilized to pretreat sugarcane bagasse (SCB) at 160 ℃ for 80 min (severity factor LogR0 = 3.67). The influences of Betaine:LA treatment on the chemical composition, crystal and microstructure structure of cellulose, and cellulase digestion were investigated. The results showed that the lignin (47.1%) and xylan (44.6%) were removed, the cellulase digestibility of Betaine:LA-treated SCB was 4.2 times that of the raw material. This improved efficiency was attributed to the enhanced accessibility of cellulose, the weakened surface area of lignin, the declined hydrophobicity, and the decreased crystallinity of cellulose. Several compelling linear correlations were fitted between enzymatic hydrolysis and these alterations of physicochemical features, comprehensively understanding enzymatic saccharification of Betaine:LA-pretreated SCB.