In vitro conversion of glycerol to lactate with thermophilic enzymes

Construction of an Artificial In Vitro Synthetic Enzymatic Platform for Upgrading Low-Cost Starch to Value-Added Disaccharides

Disaccharides are valuable oligosaccharides with an increasing demand in the food, cosmetic, and pharmaceutical industries. Disaccharides can be manufactured by extraction from the acid hydrolysate of plant-derived substrates, but this method has several issues, such as the difficulty in accessing natural substrates, laborious product separation processes, and troublesome wastewater treatment. A chemical synthesis using glucose was developed for producing disaccharides, but this approach suffers from a low product yield due to the low specificity and requires tedious protection and deprotection processes. In this study, we adopted an artificial strategy for producing a variety of value-added disaccharides from low-cost starch through the construction of an in vitro synthetic enzymatic platform: two enzymes worked in parallel to convert starch to glucose and glucose 1-phosphate, and these two intermediates were subsequently condensed together to a disaccharide by a disaccharide phosphorylase. Several disaccharides, such as laminaribiose, cellobiose, trehalose, and sophorose, were produced successfully from starch with the yields of more than 80% with the help of kinetic mathematical models to predict the optimal reaction conditions, exhibiting great potential in an industrial scale. This study provided a promising alternative to reform the mode of disaccharide manufacturing.

Facile synthesis of (-)-vibo-quercitol from maltodextrin via an in vitro synthetic enzymatic biosystem

(-)-vibo-Quercitol (VQ: 1L-1,2,4/3,5-cyclohexanepentol), a form of deoxyinositol, is an alternative chiral building block in the synthesis of bioactive compounds to control diabetes. In this study, an adenosine triphosphate-free in vitro synthetic enzymatic biosystem composed of five enzymes (including one enzyme for NADH regeneration) was constructed to produce VQ from maltodextrin in one-pot. After optimization of reaction conditions, 7.6 g/L VQ was produced from 10 g/L maltodextrin with a product yield (mol/mol) of 77%, and 25.3 g/L VQ with a purity of 87% was produced from 50 g/L maltodextrin through simple scaling up of this nonfermentative enzymatic biosystem. Therefore, this study provides an economical and environmentally friendly method for the envisioned quercitol biosynthesis.

Efficient Bioconversion of Sucrose to High-Value-Added Glucaric Acid by In Vitro Metabolic Engineering

Glucaric acid (GA) is a major value-added chemicals feedstock and additive, especially in the food, cosmetics, and pharmaceutical industries. The increasing demand for GA is driving the search for a more efficient and less costly production pathway. In this study, a new in vitro multi-enzyme cascade system was developed, which converts sucrose efficiently to GA in a single vessel. The in vitro system, which does not require adenosine triphosphate (ATP) or nicotinamide adenine dinucleotide (NAD⁺ ) supplementation, contains seven enzymes. All enzymes were chosen from the BRENDA and NCBI databases and were expressed efficiently in Escherichia coli BL21(DE3). All seven enzymes were combined in an in vitro cascade system, and the reaction conditions were optimized. Under the optimized conditions, the in vitro seven-enzyme cascade system converted 50 mm sucrose to 34.8 mm GA with high efficiency (75 % of the theoretical yield). This system represents an alternative pathway for more efficient and less costly production of GA, which could be adapted for the synthesis of other value-added chemicals.

Conversion of d-glucose to l-lactate via pyruvate by an optimized cell-free enzymatic biosystem containing minimized reactions

Cell-free synthetic enzymatic biosystem is emerging to expand the traditional biotechnological mode by utilizing a number of purified/partially purified enzymes and coenzymes in a single reaction vessel for the production of desired products from low-cost substrates. Here, a cell-free synthetic biosystem containing minimized number of reactions was designed for the conversion of d-glucose to l-lactate via pyruvate. This NADH-balanced biosystem was comprised of only 5 thermophilic enzymes without ATP supplementation. After optimization of enzyme loading amounts, buffer concentration and cofactor concentration, d-glucose was converted to l-lactate with a product yield of ∼90%. Our study has provided an emerging platform with potentials in producing pyruvate-derived chemicals, and may promote the development of cell-free synthetic enzymatic biosystems for biomanufacturing.

Deacidification of grass silage press juice by continuous production of acetoin from its lactate via an immobilized enzymatic reaction cascade

An immobilized enzymatic reaction cascade was designed and optimized for the deacidification of grass silage press juice (SPJ), thus facilitating the production of bio-based chemicals. The cascade involves a three-step process using four enzymes immobilized in a Ca-alginate gel and uses lactic acid to form acetoin, a value-added product. The reaction is performed with a continuous, pH-dependent substrate feed under oxygenation. With titrated lactic acid yields of up to 91% and reaction times of ca. 6h was achieved. Using SPJ as titrant yields of 49% were obtained within 6h. In this deacidification process, with acetoin one value-added bio-based chemical is produced while simultaneously the remaining press juice can be used in applications that require a higher pH. Such, this system can be applied in a multi-product biorefinery concept to take full advantage of nutrient-rich SPJ, which is a widely available and easily storable renewable resource.

Modules for in vitro metabolic engineering: Pathway assembly for bio-based production of value-added chemicals

Bio-based chemical production has drawn attention regarding the realization of a sustainable society. In vitro metabolic engineering is one of the methods used for the bio-based production of value-added chemicals. This method involves the reconstitution of natural or artificial metabolic pathways by assembling purified/semi-purified enzymes in vitro. Enzymes from distinct sources can be combined to construct desired reaction cascades with fewer biological constraints in one vessel, enabling easier pathway design with high modularity. Multiple modules have been designed, built, tested, and improved by different groups for different purpose. In this review, we focus on these in vitro metabolic engineering modules, especially focusing on the carbon metabolism, and present an overview of input modules, output modules, and other modules related to cofactor management.

Medium chain length polyhydroxyalkanoates consisting primarily of unsaturated 3-hydroxy-5-cis-dodecanoate synthesized by newly isolated bacteria using crude glycerol

Background

Our study aimed to search for novel bacteria capable of producing polyhydroxyalkanoates (PHAs) using crude glycerol residue obtained from biodiesel production in which used cooking oils were the substrates.

Results

Newly isolated bacteria from soils in Thailand were screened for the efficient production of PHAs from crude glycerol. The bacterial strains were cultivated on glucose, refined glycerol, crude glycerol, or various cooking oils (canola oil, palm oil, soybean oil, sunflower oil, corn oil, grape seed oil, olive oil, rice bran oil, camellia seed oil) for growth and PHA production. The effects of the total organic carbon (TOC) concentration and the mole ratio of carbon to nitrogen were investigated in batch cultivation. ¹H NMR, two dimensional-¹H-correlation spectroscopy (2D-¹H-COSY) and ¹³C NMR analyses confirmed four bacterial strains were capable of producing medium-chain-length PHAs (mcl-PHAs), consisting of 3-hydroxyoctanoate (3HO) and 3-hydroxy-5-cis-dodecanoate (3H5DD), from crude glycerol. On the basis of phenotypic features and genotypic investigations, the bacterial strains were assigned as: ASC1, Acinetobacter genus (94.9 % similarity); ASC2, Pseudomonas genus (99.2 % similarity); ASC3, Enterobacter genus (99.2 % similarity); ASC4, Bacillus genus (98.4 % similarity). The highest amount of mcl-PHAs, 17.5 ± 0.8 g/L (content 61.8 ± 3.3 % wt), with 3HO (14.7 ± 2.2 mol %), 3H5DD (85.3 ± 2.2 mol %), and a total biomass of 32.3 ± 0.3 g/L, was obtained from Pseudomonas sp. ASC2 in batch cultivation after 36 h. The mcl-PHAs recovered had a number-average molecular weight (M_N) of 3.6 × 10⁴ Da. Homopolymeric 3H5DD was obtained when the cultivation time was prolonged to 96 h.

Conclusions

Novel PHA-producing strains were isolated and identified. These bacterial strains are able to produce mcl-PHAs from crude glycerol. The mcl-PHAs produced contained a high percentage of 3H5DD, which suggests their future application as softeners mixed with other biomaterials. The unsaturated side chain of 3H5DD monomers containing double bounds offers additional potential for improving the properties of the mcl-PHAs or extending their applications to the food industry.