Heparosan biosynthesis in recombinant Bacillus megaterium: Influence of N-acetylglucosamine supplementation and kinetic modeling.

Heparosan, an unsulfated polysaccharide, plays a pivotal role as a primary precursor in the biosynthesis of heparin-an influential anticoagulant with diverse therapeutic applications. To enhance heparosan production, the utilization of metabolic engineering in nonpathogenic microbial strains is emerging as a secure and promising strategy. In the investigation of heparosan production by recombinant Bacillus megaterium, a kinetic modeling approach was employed to explore the impact of initial substrate concentration and the supplementation of precursor sugars. The adapted logistic model was utilized to thoroughly analyze three vital parameters: the B. megaterium growth dynamics, sucrose utilization, and heparosan formation. It was noted that at an initial sucrose concentration of 30 g L-1 (S1), it caused an inhibitory effect on both cell growth and substrate utilization. Intriguingly, the inclusion of N-acetylglucosamine (S2) resulted in a significant 1.6-fold enhancement in heparosan concentration. In addressing the complexities of the dual substrate system involving S1 and S2, a multi-substrate kinetic models, specifically the double Andrew's model was employed. This approach not only delved into the intricacies of dual substrate kinetics but also effectively described the relationships among the primary state variables. Consequently, these models not only provide a nuanced understanding of the system's behavior but also serve as a roadmap for optimizing the design and management of the heparosan production method.

Niclosamide inhibits Newcastle disease virus replication in chickens by perturbing the cellular glycolysis.

Newcastle disease virus (NDV), a member of Paramyxoviridae family, is one of the most important pathogens in poultry. To ensure optimal environments for their replication and spread, viruses rely largely on host cellular metabolism. In the present study, we evaluated the small drug molecule niclosamide for its anti-NDV activity. Our study has shown that a sublethal dose of 1 µM niclosamide could drastically reduce NDV replication. The results showed that niclosamide has antiviral activity against NDV infection during in vitro, in ovo and in vivo assays. Pharmacologically inhibiting the glycolytic pathway remarkably reduced NDV RNA synthesis and infectious virion production. Our results suggest that the effect of niclosamide on cellular glycolysis could be the possible reason for the specific anti-NDV effect. This study could help us understand antiviral strategies against similar pathogens and may lead to novel therapeutic approaches through targeted inhibition of specific cellular metabolic pathways.

Engineering precursor and co-factor supply to enhance D-pantothenic acid production in Bacillus megaterium.

High-yielding chemical and chemo-enzymatic methods of D-pantothenic acid (DPA) synthesis are limited by using poisonous chemicals and DL-pantolactone racemic mixture formation. Alternatively, the safe microbial fermentative route of DPA production was found promising but suffered from low productivity and precursor supplementation. In this study, Bacillus megaterium was metabolically engineered to produce DPA without precursor supplementation. In order to provide a higher supply of precursor D-pantoic acid, key genes involved in its synthesis are overexpressed, resulting strain was produced 0.53 ± 0.08 g/L DPA was attained in shake flasks. Cofactor CH2-THF was found to be vital for DPA biosynthesis and was regenerated through the serine-glycine degradation pathway. Enhanced supply of another precursor, ß-alanine was achieved by codon optimization and dosing of the limiting L-asparate-1-decarboxylase (ADC). Co-expression of Pantoate-ß-alanine ligase, ADC, phosphoenolpyruvate carboxylase, aspartate aminotransferase and aspartate ammonia-lyase enhanced DPA concentration to 2.56 ± 0.05 g/L at shake flasks level. Fed-batch fermentation in a bioreactor with and without the supplementation of ß-alanine increased DPA concentration to 19.52 ± 0.26 and 4.78 ± 0.53 g/L, respectively. This present study successfully demonstrated a rational approach combining precursor supply engineering with cofactor regeneration for the enhancement of DPA titer in recombinant B. megaterium.

High-level expression and optimization of pantoate-ß-alanine ligase in Bacillus megaterium for the enhanced biocatalytic production of D-pantothenic acid.

D-Pantothenic acid (DPA), also known as vitamin B5 is associated with several biological functions and its deficiency causes metabolic and energetic disorders in humans. Fortification of foods with DPA is the viable option to address this risk. DPA biological production route employs pantoate-ß-alanine ligase (PBL) as the key enzyme, which avoids the tedious and time-consuming optical resolution process. The selection of an efficient PBL enzyme is vital for the biological production of DPA. In this study, the panC gene encoding PBL from Escherichia coli, Bacillus megaterium, Corynebacterium glutamicum and Bacillus subtilis was expressed in B. megaterium. B. subtilis derived panC exhibited high PBL activity 61.62 ± 2.15 U/mL. Co-expression of phosphoenolpyruvate carboxykinase (pckA) did not improve the DPA production in B. megaterium. Biocatalytic fed-batch fermentation with externally supplemented precursor substrates (D-pantoic acid and ß-alanine) improved DPA titer to 45.56 ± 0.53 g/L. Daily dietary requirements of DPA for different age groups (including babies, small children, athletes and elderly people) is steadily increasing and the improved DPA production addressed in this study offers advantage for its application in fortification of food products meeting the emerging nutritional demand. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13197-021-05093-6.

One-Pot Biosynthesis of 3-Aminopropionic Acid from Fumaric Acid Using Recombinant Bacillus megaterium Containing a Linear Dual-Enzyme Cascade.

3-Aminopropionic acid (3-APA) has wide applications in food, cosmetics, pharmaceuticals, chemical, and polymer industries. This present study aimed to develop an eco-friendly whole-cell biocatalytic process for the bio-production of 3-APA from fumaric acid (FA) using Bacillus megaterium. A dual-enzyme cascade route with aspartate-1-decarboxylases (ADC) from Bacillus subtilis and native aspartate ammonia-lyase (AspA) was developed. Divergent catalytic efficiencies between these two enzymes led to an imbalance between both enzyme reactions. In order to coordinate AspA and ADC expression levels, gene mining, optimization, and duplication strategies were employed. Additionally, culture cultivation conditions and biocatalysis process parameters were optimized. A maximum 3-APA titer was obtained (11.68 ± 0.26 g/L) with a yield of 0.78 g/g under the following optimal conditions: 45 °C, pH 6.0, and 15 g/L FA. This study established a biocatalysis process for the production of 3-APA from FA using the whole cells of the recombinant B. megaterium.

Combinatorial approach for improved production of whole-cell 3-aminopropionic acid in recombinant Bacillus megaterium: codon optimization, gene duplication and process optimization.

In this study, we aimed to develop a Bacillus megaterium based whole-cell biocatalyst for the bio-production of 3-aminopropionic acid (3-APA). l-aspartate-α-decarboxylases (ADC) (EC: 4.1.1.11) from Escherichia coli, B. megaterium, Corynebacterium glutamicum, and Bacillus subtilis were expressed in B. megaterium. B. subtilis derived ADC (panD Bs ) exhibited the highest ADC activity of 0.9 ± 0.02 U/mL in recombinant B. megaterium. Combination of codon optimization and gene duplication strategies resulted in 415.56% enhancement of ADC activity compared to panD Bs . The culture growth conditions of B. megaterium (BMD-7) for 3-APA production were optimized as follows: inducer concentration, 0.5% (w/v); time of induction, 3 h; induction temperature, 37 °C and post-induction incubation time, 8 h. Improvement of the whole-cell biocatalytic process efficiency, was dealt by optimization of reaction temperature, reaction pH, metal ion additives and l-aspartic acid concentration. Shake flask level experiments yielded an enhanced 3-APA titer (16.18 ± 0.26 g/L) and a yield of 0.89 g/g under optimized conditions viz., 45 °C, pH 6.0 and 20 g/L of l-aspartic acid. This study demonstrates the potential of B. megaterium for 3-APA production and paves the scope for the development of 3-APA producing strains in near future. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13205-021-02885-7.

Application of Dual Promoter Expression System for the Enhanced Heparosan Production in Bacillus megaterium.

Heparosan, a capsular polysaccharide synthesized by certain pathogenic bacteria, is a promising precursor for heparin production. Heparosan production is catalyzed by the formation of KfiC-KfiA complex and the subsequent action of KfiC and KfiA proteins. Polycistronic expression of kfiC and kfiA in Bacillus megaterium yielded an unbalanced expression of KfiC and KfiA proteins resulted in decreased heparosan production. In this study, dual promoter plasmid system was constructed to increase the expression levels of KfiC and KfiA proteins. Dual promoter plasmid system along with UDP-glucuronic acid pathway overexpression (CADuet-DB) increased the heparosan production to 203 mg/L in shake flask experiments. Batch fermentation of strain CADuet-DB under controlled conditions yielded a maximum heparosan concentration of 627 mg/L, which is 59% higher than strain CA-DB. A modified logistic model is applied to describe the kinetics of heparosan production and biomass growth. Fed batch fermentation resulted in 3-fold enhancement in heparosan concentration (1.96 g/L), compared to batch fermentation. Nuclear magnetic resonance analysis revealed that heparosan from strain CADuet-DB was similar to Escherichia coli K5 heparosan. These results suggested that dual promoter expression system is a promising alternative to polycistronic expression system to produce heparosan in B. megaterium.

Production and characterization of low molecular weight heparosan in Bacillus megaterium using Escherichia coli K5 glycosyltransferases.

Low molecular weight heparosan is an un-sulfated polysaccharide primarily used as a precursor for heparin synthesis that has recently been used in drug delivery applications. Heparosan synthesis from recombinant bacterial systems provides a safer alternative to naturally producing pathogenic bacterial systems. In this study, we engineered a functional heparosan synthesis pathway in Bacillus megaterium by the expression of E. coli K5 kfiC and kfiA glycosyltransferase genes. Upregulation of individual UDP-sugar precursor pathway genes enhanced the heparosan production, indicating that UDP-precursor sugar concentrations were limiting the biosynthesis. The engineered B. megaterium yielded a maximum heparosan concentration of 394 mg/L in batch bioreactor. The heparosan titer was further increased to 1.32 g/L in fed-batch fermentation. Nuclear magnetic resonance analysis revealed that the chemical structure of B. megaterium derived heparosan was identical to E. coli K5 heparosan. The heparosan molecular weight varied from 31 to 60 kDa, indicating its potential as a precursor for chemoenzymatic heparin biosynthesis. This study provides an efficient process to produce heparosan from non-pathogenic B. megaterium.

Bio-transformation of Glycerol to 3-Hydroxypropionic Acid Using Resting Cells of Lactobacillus reuteri.

Lactobacillus reuteri grown in MRS broth containing 20 mM glycerol exhibits 3.7-fold up-regulation of 3-hydroxypropionic acid (3-HP) pathway genes during the stationary phase. Concomitantly, the resting cells prepared from stationary phase show enhancement in bio-conversion of glycerol, and the maximum specific productivity (q p) is found to be 0.17 g 3-HP per g CDW per hour. The regulatory elements such as catabolite repression site in the up-stream of 3-HP pathway genes are presumed for the augmentation of glycerol bio-conversion selectively in stationary phase. However, in the repression mutant, the maximum q p of 3-HP persisted in the stationary phase-derived resting cells indicating the role of further regulatory features. In the production stage, the external 3-HP concentration of 35 mM inhibits 3-HP synthesis. In addition, it has also moderated 1,3-propanediol formation, as it is a redox bio-catalysis involving NAD(+)/NADH ratio of 6.5. Repeated batch bio-transformation has been used to overcome product inhibition, and the total yield (Ypx) of 3-HP from the stationary phase-derived biomass is 3.3 times higher than that from the non-repeated mode. With the use of appropriate gene expression condition and repeated transfer of biomass, 3-HP produced in this study can be used for low-volume, high-value applications.