Biosynthesis of low-molecular-weight mannan using metabolically engineered Bacillus subtilis 168

Enhanced antioxidant activity of low-molecular-weight hyaluronan-based coatings amended with EGCG for Torreya grandis kernels preservation

Polysaccharide coating protection technology has always been a research hotspot in the field of food preservation. In this study, hyaluronic acid (HA), the widely used green polysaccharide was optimized by a free radical mediated method for covalent grafting high antioxidant epigallocatechin gallate (EGCG) to prepare copolymers (HA-EGCG) and applied to the preservation of Torreya grandis kernels. The physicochemical properties, antioxidant activities and application effect of HA-EGCG were investigated. The results found that low-molecular-weight HA (LHA) could obtain a higher grafting rate than high-molecular-weight HA (HHA), reaching 93.5 %. For structural character, the LHA-EGCG showed good stablility, which improved the surface roughness of the edible coating and the addition of EGCG significantly enhanced the antioxidant activities (p < 0.01). For application effect, LHA-EGCG coating significantly inhibit the change of appearance color, and increase of malonaldehyde, acid value, and peroxide value during long-term storage of T. grandis kernels, and could maintain its flavor to prolong quality retention. Collectively, the edible coating of HA grafted EGCG significantly prolong the quality of the kernel and has broad application potential in the field of food preservation.

Efficient production, structural characterization and bioactivity of an extracellular polysaccharide from Grifola frondosa endophytic Burkholderia sp

Endophytic bacteria Burkholderia sp. (GFB) was firstly identified and isolated from Grifola frondosa. An exopolysaccharide (GFB-MP) of GFB strain was obtained following fermentation optimization, resulting in a maximum yield of 11.36 g/L in 5 L fed-batch fermentation. GFB-MP (MW 432.05 kDa) comprised mainly galactose, glucose, and mannose with a ratio of 39.52:14.22:46.26, indicating a mannose-enriched polysaccharide. Methylation and NMR analysis revealed that GFB-MP consisted of the main chain that was repeat units →4)-α-D-Glcp-(1 → bonded →6)-β-D-Galp-1 → repeat units and three O-6-linked branched chains. Antibacterial activity suggested that GFB-MP can effectively inhibit food pathogen bacteria Listeria and Escherichia coli with inhibition ratios of 73.4 % and 81.6 %, respectively. In addition, GFB-MP exhibited remarkable growth-promoting activity on probiotics with >50 % increments of cell growth. This study demonstrates that GFB-MP has the potential for health-beneficial food. Knowledge of endophyte polysaccharides in G. frondosa is important to understand their physiological activities and symbiotic interactions.

Structural characteristics, biotechnological production and applications of exopolysaccharides from Bacillus sp.: A comprehensive review

Exopolysaccharides (EPS) produced by Bacillus species display various biological activities and characteristics such as anti-oxidant, immunomodulatory, anti-bacterial, and bioadhesive effects. These attributes confer Bacillus species broad potential applications in diverse fields such as food, medicine, environment, and agriculture. Moreover, Bacillus-derived EPS are easier to produce and yield higher quantities than plant-derived polysaccharides. Despite these advantages, Bacillus-derived EPS still encounter numerous obstacles in industrial production and commercial applications, including elevated costs, the absence of mature fermentation tank production procedures, and the lack of systematic in vivo and in vitro activity and metabolic evaluation. Therefore, it is essential to gain insight into the current status of structure, production, and applications of Bacillus-derived EPS for facilitating their future broader application. This paper provides a comprehensive overview of the current research on the production, separation, characteristics and applications of these related biological products. Furthermore, this paper summarizes the current challenges impeding industrial production of Bacillus-derived EPS, along with potential solutions, and their prospective applications in enhancing the attributes of beneficial biofilms, laying a solid scientific foundation for the applications of Bacillus-derived EPS in industry and agriculture.

De novo engineering riboflavin production Bacillus subtilis by overexpressing the downstream genes in the purine biosynthesis pathway

BACKGROUND

Bacillus subtilis is widely used in industrial-scale riboflavin production. Previous studies have shown that targeted mutagenesis of the ribulose 5-phosphate 3-epimerase in B. subtilis can significantly enhance riboflavin production. This modification also leads to an increase in purine intermediate concentrations in the medium. Interestingly, B. subtilis exhibits remarkable efficiency in purine nucleoside synthesis, often exceeding riboflavin yields. These observations highlight the importance of the conversion steps from inosine-5'-monophosphate (IMP) to 2,5-diamino-6-ribosylamino-4(3 H)-pyrimidinone-5'-phosphate (DARPP) in riboflavin production by B. subtilis. However, research elucidating the specific impact of these reactions on riboflavin production remains limited.

RESULT

We expressed the genes encoding enzymes involved in these reactions (guaB, guaA, gmk, ndk, ribA) using a synthetic operon. Introduction of the plasmid carrying this synthetic operon led to a 3.09-fold increase in riboflavin production compared to the control strain. Exclusion of gmk from the synthetic operon resulted in a 36% decrease in riboflavin production, which was further reduced when guaB and guaA were not co-expressed. By integrating the synthetic operon into the genome and employing additional engineering strategies, we achieved riboflavin production levels of 2702 mg/L. Medium optimization further increased production to 3477 mg/L, with a yield of 0.0869 g riboflavin per g of sucrose.

CONCLUSION

The conversion steps from IMP to DARPP play a critical role in riboflavin production by B. subtilis. Our overexpression strategies have demonstrated their effectiveness in overcoming these limiting factors and enhancing riboflavin production.

Structural characterization and high-efficiency prebiotic activity of the polysaccharide from Tremella aurantialba endophytic bacteria

Herein, the low-molecular-weight heteropolysaccharide (designated as TABP), with a weight-average Mw of 5408 Da, was produced by the endophytic bacterium Bacillus sp. TAB, which was initially isolated from the fruiting bodies of the wild Tremella aurantialba. A relatively high TABP accumulation was obtained and enhanced to 6.94 g/L in 5 L fed-batch fermentation by high-density cultivation. Monosaccharide composition analysis showed that the TABP comprised arabinose, glucosamine, galactose, glucose, and mannose with a molar ratio of 0.073: 0.145: 0.406: 0.182: 0.195, respectively. Methylation and NMR analyses indicated that TABP contained 1,4-linked β-d-Galp and 1,4-linked β-d-Manp pyranosyl backbone, extensively substituted at the side chains to form a complex structure. Prebiotic potential analysis exhibited significant growth-promoting effects for various lactic acid bacteria by more than 90 %. Overall, this study initially provides valuable insights into the endophytic exopolysaccharides from T. aurantialba and their biological activity, which provides prospective sources of prebiotics for functional foods and aids in understanding the endophytes symbiosis mechanism in edible mushrooms.

Advanced strategies for metabolic engineering of Bacillus to produce extracellular polymeric substances

Extracellular polymeric substances are mainly synthesized via a variety of biosynthetic pathways in bacteria. Bacilli-sourced extracellular polymeric substances, such as exopolysaccharides (EPS) and poly-γ-glutamic acid (γ-PGA), can serve as active ingredients and hydrogels, and have other important industrial applications. However, the functional diversity and widespread applications of these extracellular polymeric substances, are hampered by their low yields and high costs. Biosynthesis of extracellular polymeric substances is very complex in Bacillus, and there is no detailed elucidation of the reactions and regulations among various metabolic pathways. Therefore, a better understanding of the metabolic mechanisms is required to broaden the functions and increase the yield of extracellular polymeric substances. This review systematically summarizes the biosynthesis and metabolic mechanisms of extracellular polymeric substances in Bacillus, providing an in-depth understanding of the relationships between EPS and γ-PGA synthesis. This review provides a better clarification of Bacillus metabolic mechanisms during extracellular polymeric substance secretion and thus benefits their application and commercialization.

A Poly-D-Mannose Synthesized by a One-Pot Method Exhibits Anti-Biofilm, Antioxidant, and Anti-Inflammatory Properties In Vitro

In this study, D-mannose was used to synthesize poly-D-mannose using a one-pot method. The molecular weight, degree of branching, monosaccharide composition, total sugar content, and infrared spectrum were determined. In addition, we evaluated the safety and bioactivity of poly-D-mannose including anti-pathogen biofilm, antioxidant, and anti-inflammatory activity. The results showed that poly-D-mannose was a mixture of four components with different molecular weights. The molecular weight of the first three components was larger than 410,000 Da, and that of the fourth was 3884 Da. The branching degree of poly-D-mannose was 0.53. The total sugar content was 97.70%, and the monosaccharide was composed only of mannose. The infrared spectra showed that poly-D-mannose possessed characteristic groups of polysaccharides. Poly-D-mannose showed no cytotoxicity or hemolytic activity at the concentration range from 0.125 mg/mL to 8 mg/mL. In addition, poly-D-mannose had the best inhibition effect on Salmonella typhimurium at the concentration of 2 mg/mL (68.0% ± 3.9%). The inhibition effect on Escherichia coli O157:H7 was not obvious, and the biofilm was reduced by 37.6% ± 2.9% at 2 mg/mL. For Staphylococcus aureus and Bacillus cereus, poly-D-mannose had no effect on biofilms at low concentration; however, 2 mg/mL of poly-D-mannose showed inhibition rates of 33.7% ± 6.4% and 47.5% ± 4%, respectively. Poly-D-mannose showed different scavenging ability on free radicals. It showed the best scavenging effect on DPPH, with the highest scavenging rate of 74.0% ± 2.8%, followed by hydroxyl radicals, with the scavenging rate of 36.5% ± 1.6%; the scavenging rates of superoxide anion radicals and ABTS radicals were the lowest, at only 10.1% ± 2.1% and 16.3% ± 0.9%, respectively. In lipopolysaccharide (LPS)-stimulated macrophages, poly-D-mannose decreased the secretion of nitric oxide (NO) and reactive oxygen species (ROS), and down-regulated the expression of tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6). Therefore, it can be concluded that poly-D-mannose prepared in this research is safe and has certain biological activity. Meanwhile, it provides a new idea for the development of novel prebiotics for food and feed industries or active ingredients used for pharmaceutical production in the future.

Screening and identification of genes involved in β-alanine biosynthesis in Bacillus subtilis

β-alanine is the only naturally occurring β-amino acid, which is widely used in medicine, food, and feed fields, and generally produced through synthetic biological methods based on engineered strains of Escherichia coli or Corynebacterium glutamicum. However, the β-alanine biosynthesis in Bacillus subtilis, a traditional industrial model microorganism of food safety grade, has not been thoroughly explored. In this study, the native l-aspartate-α-decarboxylase was overexpressed in B. subtilis 168 to obtain an increase of 842% in β-alanine production. A total of 16 single-gene knockout strains were constructed to block the competitive consumption pathways to identify a total of 6 genes (i.e., ptsG, fbp, ydaP, yhfS, mmgA, and pckA) involved in β-alanine synthesis, while the multigene knockout of these 6 genes obtained an increased β-alanine production by 40.1%. Ten single-gene suppression strains with the competitive metabolic pathways inhibited revealed that the inhibited expressions of genes glmS, accB, and accA enhanced the β-alanine production. The introduction of heterologous phosphoenolpyruvate carboxylase increased the β-alanine production by 81.7%, which was 17-fold higher than that of the original strain. This was the first study using multiple molecular strategies to investigate the biosynthetic pathway of β-alanine in B. subtilis and to identify the genetic factors limiting the excessive synthesis of β-alanine by microorganisms.

Combinatorial metabolic engineering enables high yield production of α-arbutin from sucrose by biocatalysis

α-Arbutin has been widely used as a skin-whitening ingredient. Previously, we successfully produced α-arbutin via whole-cell biocatalysis and found that the conversion rate of sucrose to α-arbutin was low (~45%). To overcome this issue, herein, we knocked out the genes of enzymes related to the sucrose hydrolysis, including sacB, sacC, levB, and sacA. The sucrose consumption was reduced by 17.4% in 24 h, and the sucrose conversion rate was increased to 51.5%. Furthermore, we developed an inducible protein degradation system with Lon protease isolated from Mesoplasma florum (MfLon) and proteolytic tag to control the PfkA activity, so that more fructose-6-phosphate (F6P) can be converted into glucose-1-phosphate (Glc1P) for α-arbutin synthesis, which can reduce the addition of sucrose and increase the sucrose conversion efficiency. Finally, the pathway of F6P to Glc1P was enhanced by integrating another copy of glucose 6-phosphate isomerase (Pgi) and phosphoglucomutase (PgcA); a high α-arbutin titer (~120 g/L) was obtained. The sucrose conversion rate was increased to 60.4% (mol/mol). In this study, the substrate utilization rate was boosted due to the attenuation of its hydrolysis and the assistance of the intracellular enzymes that converted the side product back into the substrate for α-arbutin synthesis. This strategy provides a new idea for the whole-cell biocatalytic synthesis of other products using sucrose as substrate, especially valuable glycosides.Key points The genes of sucrose metabolic pathway were knocked out to reduce the sucrose consumption. The by-product fructose was reused to synthesize α-arbutin. The optimized whole-cell system improved sucrose conversion by 15.3%.

Bacillales: From Taxonomy to Biotechnological and Industrial Perspectives

For a long time, the genus Bacillus has been known and considered among the most applicable genera in several fields. Recent taxonomical developments resulted in the identification of more species in Bacillus-related genera, particularly in the order Bacillales (earlier heterotypic synonym: Caryophanales), with potential application for biotechnological and industrial purposes such as biofuels, bioactive agents, biopolymers, and enzymes. Therefore, a thorough understanding of the taxonomy, growth requirements and physiology, genomics, and metabolic pathways in the highly diverse bacterial order, Bacillales, will facilitate a more robust designing and sustainable production of strain lines relevant to a circular economy. This paper is focused principally on less-known genera and their potential in the order Bacillales for promising applications in the industry and addresses the taxonomical complexities of this order. Moreover, it emphasizes the biotechnological usage of some engineered strains of the order Bacillales. The elucidation of novel taxa, their metabolic pathways, and growth conditions would make it possible to drive industrial processes toward an upgraded functionality based on the microbial nature.

Glucomannan in Dendrobium catenatum: Bioactivities, Biosynthesis and Perspective

Dendrobium catenatum is a classical and precious dual-use plant for both medicine and food in China. It was first recorded in Shen Nong's Herbal Classic, and has the traditional functions of nourishing yin, antipyresis, tonifying the stomach, and promoting fluid production. The stem is its medicinal part and is rich in active polysaccharide glucomannan. As an excellent dietary fiber, glucomannan has been experimentally confirmed to be involved in anti-cancer, enhancing immunity, lowering blood sugar and blood lipids, etc. Here, the status quo of the D. catenatum industry, the structure, bioactivities, biosynthesis pathway and key genes of glucomannan are systematically described to provide a crucial foundation and theoretical basis for understanding the value of D. catenatum and the potential application of glucomannan in crop biofortification.

Purification, characterization and immunostimulatory activity of a novel exopolysaccharide from Bacillus sp. H5

Crude exopolysaccharides from extracellular polymeric substances produced by the marine bacterium Bacillus sp. H5 were fractionated using DEAE-Sepharose FF and Sephadex G-75 chromatography. The high molecular weight fraction (89.0 kD) from the neutral fraction was designated EPS5SH; it contained mannose, glucosamine, glucose, and galactose in a molar ratio of 1.00: 0.02: 0.07: 0.02. Infra-red, gas chromatography-mass spectrometry, electrospray ionisation-tandem mass spectrometry analysis and nuclear magnetic resonance revealed EPS5SH was a mannan with α-(1 → 4)-Manp, α-(1 → 2)-Manp, α-(1 → 4, 6)-Manp and β-terminal-Manp. Preliminary in vitro experiments revealed that EPS5SH significantly upregulated nitric oxide synthesis and release of pro-inflammatory factors in murine macrophage RAW264.7 cells. Western blot experiments verified the immunostimulatory effects of EPS5SH through the modulation of the NF-κB and MAPK signalling pathways. In conclusion, EPS5SH was a novel immunostimulatory mannan.