Effects of medium components in a glycerol-based medium on vitamin K (menaquinone-7) production by Bacillus subtilis natto in biofilm reactors

Scaling up biofilm bioreactors for enhanced menaquinone-7 production

The health benefits of menaquinone-7 (MK-7) are well-established, and its production through fermentation techniques is widespread. Our team developed an innovative biofilm reactor utilizing Bacillus subtilis natto cells to foster biofilm growth on plastic composite supports to produce MK-7. The scalability of this biofilm reactor from a 2-L benchtop scale in our laboratory and its potential for commercial applications pose significant unresolved questions. Therefore, the current research was aimed to scale up the biofilm reactor from bench scale (2-L) to the pilot scale (30-L) bioreactor. Three strategies were evaluated to understand their impact on MK-7 biosynthesis during bioreactor volume expansion: volumetric oxygen mass transfer coefficient (kLa), agitation power input per unit volume (P/V), and impeller tip velocity (Vtip). While kLa was successfully maintained during scaling, P/V and Vtip varied and were assessed for their influence on MK-7 production. After investigating these methods, it was found that the volumetric oxygen mass transfer coefficient (kLa) constant method proved to be the most effective one. The optimum MK-7 concentration achieved was 21.0 ± 1.0 mg/L, comparable to the highest MK-7 concentration of 20.6 ± 1.0 attained at the 2-L scale. This showcases the scalability of biofilm bioreactor technology and its promising potential for commercial production of MK-7. Furthermore, we explored the potential of fed-batch glucose addition to the base media in the biofilm reactor to enhance MK-7 concentration at the 30-L scale. Remarkably, results demonstrated that fed-batch strategy significantly increased MK-7 concentrations to 28.7 ± 0.3 mg/L, which made it almost 2.3-fold higher than levels produced in suspended-cell bioreactors. This finding highlights the potential of biofilm reactors as a promising replacement to the current static fermentation strategies for commercial production of MK-7.

Enhancing menaquinone-7 biosynthesis by optimized fermentation strategies and fed-batch cultivation of food-derived Bacillus subtilis

BACKGROUND

Menaquinone-7 (MK-7), a type of vitamin K2 (VK2), is considered to be a health-promoting functional ingredient in the current recommended dietary supply. However, it is a challenge to isolate high-yield MK-7-producing strains with reasonable safety from natural food, which further limits their use as starter culture.

RESULTS

In this study, an MK-7 production strain derived from commercial natto with a yield of 2.33 ± 0.06 mg L-1, Bacillus subtilis 4-b4, was screened using a selective medium containing rotenone combined with a VK2 enzyme-linked immunosorbent assay kit, and high-performance liquid chromatography. This strain exhibited excellent safety with no hemolysis, excellent antioxidant activity, and sensitivity to antibiotics. Furthermore, its fermentation strategies (fermentation condition and the supply of key precursor substances) were optimized to improve MK-7 biosynthesis. As a result, the yield increased 3.31-fold, reaching 7.70 ± 0.24 mg L-1 at shake flask fermentation level. After scaling up through fed-batch fermentation, the yield further increased to 23.43 ± 0.41 mg L-1 in a 5 L bioreactor.

CONCLUSION

The current study developed a strain with good safety and antibiotic sensitivity for producing MK-7, and improved its biosynthesis through optimized fermentation strategies and scaling up the process, laying the foundation for the availability of biologically active MK-7 fermented food in the food industry. © 2025 Society of Chemical Industry.

Effects of Monascus pilosus SWM 008-Fermented Red Mold Rice and Its Functional Components on Gut Microbiota and Metabolic Health in Rats

Red mold rice, fermented by Monascus spp., has been reported to modulate gut microbiota composition and improve metabolic health. Previous studies indicate that red mold rice can reduce cholesterol, inhibit hepatic lipid accumulation, and enhance bile acid excretion, while also altering gut microbiota under high-fat dietary conditions. However, it remains unclear whether these effects are directly due to Monascus-derived products modulating gut microbiota or are a consequence of improved metabolic health conditions, which indirectly influence gut microbiota. This study aimed to evaluate the effects of Monascus pilosus SWM 008 fermented red mold rice and its components-monascin, monascinol, ankaflavin, and polysaccharides-on gut microbiota and metabolic health in rats fed a normal diet. Over eight weeks, physiological, biochemical, and gut microbiota parameters were assessed. Results showed no significant changes in body weight or liver/kidney function, confirming safety. Gut microbiota analysis revealed that red mold rice, monascin, monascinol, and polysaccharides significantly altered gut microbiota composition by increasing the relative abundance of beneficial bacteria, such as Akkermansia muciniphila, Ligilactobacillus murinus, and Duncaniella dubosii. Functional predictions indicated enhanced vitamin K2 biosynthesis, nucleotide metabolism, and other metabolic pathways linked to improved gut health. In conclusion, Monascus pilosus SWM 008 fermented red mold rice demonstrated safety and beneficial effects, suggesting its potential as a functional food to maintain gut microbiota balance under normal dietary conditions.

Exploring the potential of soapstock over a glycerol in vitamin K2 production by Bacillus subtilis natto: a comparative analysis

BACKGROUND

Vitamin K2 is an essential nutrient for blood coagulation and cardiovascular health and mainly produced by bacteria strain like B. subtilis. researchers have explored producing strain improvement, cultivation mode, environmental optimization, increased secretion, and using cheaper carbon and nitrogen sources in order to increase vitamin K2 productivity. This study examines the impact of varioius concentration of soapstock, which is a by-product of vegetable oil refining, as an alternative carbon source with lower pirce, in the fermentation medium instead of glycerol on the microbial synthesis of vitamin K2 using B. subtilis natto ATCC 23857.

RESULTS

The results demonstrate that when the glycerol in fermentation medium was substituted with soapstock, by 75% concentartion, the fermentation process produced a yield of 158.16 mg/L of vitamin K2 after 72 h; This was 3.8 times more than the control medium containing glycerol. When the entire culture medium was replaced with wastewater, the vitamin K2 concentration reached 21.18 mg/L, 52% of the control medium's concentration. If the carbon sources in the fermentation medium consisted of 20% soapstock and 47.4 g/L glycerol (maintaining the same final glycerol concentration as the control medium), the vitamin K2 concentration reached 35.7 mg/L or 85.8% of the control medium. The analysis of soapstock fermentation medium characteristics reveals that after fermentation with B. subtilis, the COD of soapstock fermentation medium was dramatically reduced from 259,500 mg/L to 57,830 mg/L.

CONCLUSIONS

Using soapstock as an alternative carbon source for fermentation did not negatively impact the bioprocess and increased vitamin K2 production. Therefore, this research introduces an alternative carbon resource for vitamin K2 production and paves the way for the biorefinement of soapstock.

Microbial biofilms as a platform for diverse biocatalytic applications

Microbial biofilms have gained significant traction in commercial wastewater treatment due to their inherent resilience, well-organized structure, and potential for collaborative metabolic processes. As our understanding of their physiology deepens, these living catalysts are finding exciting applications beyond wastewater treatment, including the production of bulk and fine chemicals, bioelectricity generation, and enzyme immobilization. While the biological applications of biofilms in different biocatalytic systems have been extensively summarized, the applications of artificially engineered biofilms were rarely discussed. This review aims to bridge this gap by highlighting the untapped potential of engineered microbial biofilms in diverse biocatalytic applications, with a focus on strategies for biofilms engineering. Strategies for engineering biofilm-based systems will be explored, including genetic modification, synthetic biology approaches, and targeted manipulation of biofilm formation processes. Finally, the review will address key challenges and future directions in developing robust biofilm-based biocatalytic platforms for large-scale production of chemicals, pharmaceuticals, and biofuels.

Colorimetric screening model for identification of menaquinone-7 (MK-7) producing strains

In this study, a novel colorimetric screening method for identifying menaquinone-7 (MK-7) producing strains was established using potassium permanganate. To our knowledge, this method represents the first direct screening methodology for the identification of MK-7 producing strains. Utilizing this screening method, a new MK-7 producing strain, Bacillus subtilis GSA-184, was identified from the soil of the Tibetan Plateau. Under the optimized fermentation medium (50 g/L glycerol, 30 g/L yeast extract powder, 100 g/L soybean peptone, 1 g/L KH2PO4, and 1 g/L MnSO4), the production of MK-7 was increased to 25.7 mg/L. Additionally, the maximum production of MK-7 reached 36.46 mg/L after 48 h in a 5-L fermenter.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-04097-1.

Sustainable menaquinone-7 production through continuous fermentation in biofilm bioreactors

Menaquinone-7 (MK-7), a vital vitamin with numerous health benefits, is synthesized and secreted extracellularly by the formation of biofilm, dominantly in Bacillus strains. Our team developed an innovative biofilm reactor utilizing Bacillus subtilis natto cells to foster biofilm growth on plastic composite supports to produce MK-7. Continuous fermentation in biofilm reactors offers a promising strategy for achieving sustainable and efficient production of Menaquinone-7 (MK-7). Unlike conventional batch fermentation, continuous biofilm reactors maintain a steady state of operation, which reduces resource consumption and waste generation, contributing to sustainability. By optimizing fermentation conditions, MK-7 production was significantly enhanced in this study, demonstrating the potential for sustainable industrial-scale production. To determine the optimal operational parameters, various dilution rates were tested. These rates were selected based on their potential to enhance nutrient supply and biofilm stability, thereby improving MK-7 production. By carefully considering the fermentation conditions and systematically varying the dilution rates, MK-7 production was significantly enhanced during continuous fermentation. The MK-7 productivity was found to increase from 0.12 mg/L/h to 0.33 mg/L/h with a dilution rate increment from 0.007 to 0.042 h-1). This range was chosen to explore the impact of various nutrient supply rates on MK-7 production and to identify the optimal conditions for maximizing productivity. However, a further increase in the dilution rate to 0.084 h-1 led to reduced productivity at approximately 0.16 mg/L/h, likely due to insufficient retention time for effective biofilm formation. Consequently, a dilution rate of 0.042 h-1 exhibited the highest productivity of 0.33 mg/L/h, outperforming all investigated dilution rates and demonstrating the critical balance between nutrient supply and retention time in continuous fermentation. These findings validate the feasibility of operating continuous fermentation at a 0.084 h-1 dilution rate, corresponding to a 48 h retention time, to achieve the highest MK-7 productivity compared to conventional batch fermentation. The significant advancements achieved in enhancing Menaquinone-7 (MK-7) productivity through continuous fermentation at optimal dilution rates in the present work indicate promising prospects for even greater efficiency and sustainability in MK-7 production through future developments.

Comparative genomics analysis and transposon mutagenesis provides new insights into high menaquinone-7 biosynthetic potential of Bacillus subtilis natto

This research combined Whole-Genome sequencing, intraspecific comparative genomics and transposon mutagenesis to investigate the menaquinone-7 (MK-7) synthesis potential in Bacillus subtilis natto. First, Whole-Genome sequencing showed that Bacillus subtilis natto BN-P15-11-1 contains one single circular chromosome in size of 3,982,436 bp with a GC content of 43.85 %, harboring 4,053 predicted coding genes. Next, the comparative genomics analysis among strain BN-P15-11-1 with model Bacillus subtilis 168 and four typical Bacillus subtilis natto strains proves that the closer evolutionary relationship Bacillus subtilis natto BN-P15-11-1 and Bacillus subtilis 168 both exhibit strong biosynthetic potential. To further dig for MK-7 biosynthesis latent capacity of BN-P15-11-1, we constructed a mutant library using transposons and a high throughput screening method using microplates. We obtained a YqgQ deficient high MK-7 yield strain F4 with a yield 3.02 times that of the parent strain. Experiments also showed that the high yield mutants had defects in different transcription and translation regulatory factor genes, indicating that regulatory factor defects may affect the biosynthesis and accumulation of MK-7 by altering the overall metabolic level. The findings of this study will provide more novel insights on the precise identification and rational utilization of the Bacillus subtilis subspecies for biosynthesis latent capacity.

Brij-58 supplementation enhances menaquinone-7 biosynthesis and secretion in Bacillus natto

Menaquinone-7 is a form of vitamin K2 that has been shown to have numerous healthy benefits. In this study, several surfactants were investigated to enhance the production of menaquinone-7 in Bacillus natto. Results showed that Brij-58 supplementation influenced the cell membrane via adsorption, and changed the interfacial tension of fermentation broth, while the changes in the state and the composition of the cell membrane enhanced the secretion and biosynthesis of menaquinone-7. The total production and secretion rate of menaquinone-7 increased by 48.0% and 56.2% respectively. During fermentation, the integrity of the cell membrane decreased by 82.9% while the permeability increased by 158% when the maximum secretory rate was reached. Furthermore, Brij-58 supplementation induced the stress response in bacteria, resulting in hyperpolarization of the membrane, and increased membrane ATPase activity. Finally, changes in fatty acid composition increased membrane fluidity by 30.1%. This study provided an effective strategy to enhance menaquinone-7 yield in Bacillus natto and revealed the mechanism of Brij-58 supplementation in menaquinone-7 production. KEY POINTS: • MK-7 yield in Bacillus natto was significantly increased by Brij-58 supplementation. • Brij-58 could be adsorbed on cell surface and change fermentation environment. • Brij-58 supplementation could affect the state and composition of the cell membrane.

The Effect of Iron Oxide Nanoparticles on the Menaquinone-7 Isomer Composition and Synthesis of the Biologically Significant All-Trans Isomer

Menaquinone-7 (MK-7) is the most therapeutically valuable K vitamin owing to its excellent bioavailability. MK-7 occurs as geometric isomers, and only all-trans MK-7 is bioactive. The fermentation-based synthesis of MK-7 entails various challenges, primarily the low fermentation yield and numerous downstream processing steps. This raises the cost of production and translates to an expensive final product that is not widely accessible. Iron oxide nanoparticles (IONPs) can potentially overcome these obstacles due to their ability to enhance fermentation productivity and enable process intensification. Nevertheless, utilisation of IONPs in this regard is only beneficial if the biologically active isomer is achieved in the greatest proportion, the investigation of which constituted the objective of this study. IONPs (Fe₃O₄) with an average size of 11 nm were synthesised and characterised using different analytical techniques, and their effect on isomer production and bacterial growth was assessed. The optimum IONP concentration (300 μg/mL) improved the process output and resulted in a 1.6-fold increase in the all-trans isomer yield compared to the control. This investigation was the first to evaluate the role of IONPs in the synthesis of MK-7 isomers, and its outcomes will assist the development of an efficient fermentation system that favours the production of bioactive MK-7.

Optimisation of the fermentation media to enhance the production of the bioactive isomer of vitamin menaquinone-7

Menaquinone-7 (MK-7) offers significant health benefits; however, only the all-trans form is biologically active. MK-7 produced through fermentation can occur as all-trans and cis isomers, and the therapeutic value of the resulting MK-7 is exclusively determined by the quantity of the all-trans isomer. Therefore, this study aimed to investigate the effect of the media composition on the isomer profile obtained from fermentation and determine the optimum media combination to increase the concentration of the all-trans isomer and diminish the production of cis MK-7. For this purpose, design of experiments (DOE) was used to screen the most effective nutrients, and a central composite face-centred design (CCF) was employed to optimise the media components. The optimum media consisted of 1% (w/v) glucose, 2% (w/v) yeast extract, 2% (w/v) soy peptone, 2% (w/v) tryptone, and 0.1% (w/v) CaCl2. This composition resulted in an average all-trans and cis isomer concentration of 36.366 mg/L and 1.225 mg/L, respectively. In addition, the optimised media enabled an all-trans isomer concentration 12.2-fold greater and a cis isomer concentration 2.9-fold less than the unoptimised media. This study was the first to consider the development of an optimised fermentation media to enhance the production of the bioactive isomer of MK-7 and minimise the concentration of the inactive isomer. Furthermore, this media is commercially promising, as it will improve the process productivity and reduce the costs associated with the industrial fermentation of the vitamin.

Effects of Alkali Stress on the Growth and Menaquinone-7 Metabolism of Bacillus subtilis natto

Menaquinone-7 (MK-7) is an important vitamin K₂, synthesized from the menaquinone parent ring and seven isoprene side chains. Presently, the synthesis of MK-7 stimulated by environmental stress primarily focuses on oxygen stress, while the effect of alkali stress is rarely studied. Therefore, this study researched the effects of alkali stress on the fermentation performance and gene expression of Bacillus subtilis natto. The organism’s growth characteristics, biomass, sporogenesis, MK-7 biosynthesis, and gene expression were analyzed. After a pH 8.5 stress adaptation treatment for 0.5 h and subsequent fermentation at pH 8.5, which promoted the growth of the strain and inhibited the spore formation rate. In addition, biomass was significantly increased (P < 0.05). The conversion rate of glycerol to MK-7 was 1.68 times higher than that of the control group, and the yield of MK-7 increased to 2.10 times. Transcriptomic analysis showed that the MK-7 high-yielding strain had enhanced carbon source utilization, increased glycerol and pyruvate metabolism, enhanced the Embden-Meyerhof pathway (EMP), tricarboxylic acid (TCA) circulation flux, and terpenoid biosynthesis pathway, and promoted the accumulation of acetyl-CoA, the side-chain precursor of isoprene. At the same time, the up-regulation of transketolase increased the metabolic flux of the pentose phosphate (HMP) pathway, which was conducive to the accumulation of D-erythrose 4-phosphate, the precursor of the menadione parent ring. This study’s results contribute to a better understanding of the effects of environmental stress on MK-7 fermentation by Bacillus subtilis natto and the molecular regulatory mechanism of MK-7 biosynthesis.

Production of Vitamin K by Wild-Type and Engineered Microorganisms

Vitamin K is a fat-soluble vitamin that mainly exists as phylloquinone or menaquinone in nature. Vitamin K plays an important role in blood clotting and bone health in humans. For use as a nutraceutical, vitamin K is produced by natural extraction, chemical synthesis, and microbial fermentation. Natural extraction and chemical synthesis methods for vitamin K production have limitations, such as low yield of products and environmental concerns. Microbial fermentation is a more sustainable process for industrial production of natural vitamin K than two other methods. Recent advanced genetic technology facilitates industrial production of vitamin K by increasing the yield and productivity of microbial host strains. This review covers (i) general information about vitamin K and microbial host, (ii) current titers of vitamin K produced by wild-type microorganisms, and (iii) vitamin K production by engineered microorganisms, including the details of strain engineering strategies. Finally, current limitations and future directions for microbial production of vitamin K are also discussed.

Advances in Enhanced Menaquinone-7 Production From Bacillus subtilis

The production of nutraceutical compounds through biosynthetic approaches has received considerable attention in recent years. For example, Menaquinone-7 (MK-7), a sub-type of Vitamin K2, biosynthesized from Bacillus subtilis (B. subtilis), proved to be more efficiently produced than the conventional chemical synthesis techniques. This is possible due to the development of B. subtilis as a chassis cell during the biosynthesis stages. Hence, it is imperative to provide insights on the B. subtilis membrane permeability modifications, biofilm reactors, and fermentation optimization as advanced techniques relevant to MK-7 production. Although the traditional gene-editing method of homologous recombination improves the biosynthetic pathway, CRISPR-Cas9 could potentially resolve the drawbacks of traditional genome editing techniques. For these reasons, future studies should explore the applications of CRISPRi (CRISPR interference) and CRISPRa (CRISPR activation) system gene-editing tools in the MK-7 anabolism pathway.

Combinatorial Methylerythritol Phosphate Pathway Engineering and Process Optimization for Increased Menaquinone-7 Synthesis in Bacillus subtilis

Vitamin K2 (menaquinone) is an essential vitamin existing in the daily diet, and menaquinone-7 (MK-7) is an important form of it. In a recent work, we engineered the synthesis modules of MK-7 in Bacillus subtilis, and the strain BS20 could produce 360 mg/l MK-7 in shake flasks, while the methylerythritol phosphate (MEP) pathway, which provides the precursor isopentenyl diphosphate for MK-7 synthesis, was not engineered. In this study, we overexpressed five genes of the MEP pathway in BS20 and finally obtained a strain (BS20DFHG) with MK-7 titer of 415 mg/l in shake flasks. Next, we optimized the fermentation process parameters (initial pH, temperature and aeration) in an 8-unit parallel bioreactor system consisting of 300-ml glass vessels. Based on this, we scaled up the MK-7 production by the strain BS20DFHG in a 50-l bioreactor, and the highest MK-7 titer reached 242 mg/l. Here, we show that the engineered strain BS20DFHG may be used for the industrial production of MK-7 in the future.

Economical production of vitamin K2 using crude glycerol from the by-product of biodiesel

Industrial waste, such as crude glycerol, was used for vitamin K₂ by B. subtilis Z-15. Crude glycerol could be used instead of pure glycerin for vitamin K₂ production. The combination of soybean peptone and yeast extract was more conducive to the synthesis of vitamin K₂. The optimal composition of medium was obtained by response surface methodology. The results indicated that the optimal medium was as follows: 6.3% crude glycerol, 3.0% soybean peptone concentration and 5.1 g/L yeast extract. Under the optimal culture medium, vitamin K₂ production was increased to 45.11 ± 0.62 mg/L. The fermentor test further proved that the use of crude glycerol affected neither the synthesis of vitamin K₂ nor the growth of B. subtilis. These investigations could lay a foundation for reducing the pollution of crude glycerol, exploring a late model for vitamin K₂ cleaner production.

Screening of pectinase-producing bacteria from farmlands and optimization of enzyme production from selected strain by RSM

Pectinolytic enzymes that catalyze the breakdown of substrates containing pectin are widespread. Pectinases have potential applications in various industries, including food, animal feed, textile, paper, and fuel. In this study, one hundred bacterial isolates were collected from Marand city farmlands (Azarbaijan-E-Sharqi, Iran) and screened by MP medium on the base of pectinase activity considering the significance of pectinases. The results depicted that three isolates showed the most pectinase activity (more massive halo). The biochemical and molecular test results showed that the three screened bacteria were Enterobacter and named Enterobacter sp. MF41, Enterobacter sp. MF84, and Enterobacter sp. MF90. Enterobacter sp. MF84 had the largest halo, so this strain was selected for the study of its produced pectinase. The results exhibited that the produced enzyme has optimum temperature and pH for activity at 30 °C and in 9, respectively. Finally, the enzyme production by Enterobacter sp. MF84 is optimized using response surface methodology (RSM) considering four factors (NH₄Cl, K₂HPO₄, pectin, and incubation time) as variables. The results showed that the optimization procedure increased the enzyme production up to 12 times (from 1.16 to 14.16 U/mg). The Pareto analysis revealed that ammonium chloride has a significant role in decreasing the enzyme production, probably by inducing the nitrification pathway enzymes in the presence of organic nitrogen in Enterobacter sp. MF84.

Cis and trans isomers of the vitamin menaquinone-7: which one is biologically significant?

Recently, several studies have indicated that an adequate intake of menaquinone-7 (MK-7) offers numerous health benefits. However, the low availability of MK-7 in the diet necessitates the development of dietary supplements or functional food products to complement natural food sources and meet the daily intake requirements. Like most biological molecules, MK-7 can exist as geometric isomers that can occur in the cis, trans, and cis/trans forms; however, only the all-trans form is biologically significant. MK-7 is traditionally produced through bacterial fermentation, but various synthetic preparations have lately become available. The isomer composition in the final product is influenced by numerous factors, including the methods of production and purification, as well as particular environmental and storage conditions. The MK-7 profile obtained from the various production methods has not yet been elucidated, and the ideal method for the synthesis of the all-trans form of the vitamin is also debatable. Consequently, the quantification of the MK-7 profile of various products is necessary to develop an understanding of the factors that influence the proportion of isomers that are obtained in different preparations. Several possible methods exist for the quantification of MK-7 isomers, and of these, liquid chromatography in conjunction with mass spectrometry techniques appears to be the most promising. Evaluation of the isomer composition is an important consideration, as only the all-trans form sustains biological activity. Furthermore, knowledge of the prominent factors that influence the MK-7 composition may also enable their manipulation to obtain a more favorable MK-7 profile in the final product.

Microbial production of vitamin K2: current status and future prospects

Vitamin K2, also called menaquinone, is an essential lipid-soluble vitamin that plays a critical role in blood clotting and prevention of osteoporosis. It has become a focus of research in recent years and has been widely used in the food and pharmaceutical industries. This review will briefly introduce the functions and applications of vitamin K2 first, after which the biosynthesis pathways and enzymes will be analyzed in-depth to highlight the bottlenecks facing the microbial vitamin K2 production on the industrial scale. Then, various strategies, including strain mutagenesis and genetic modification, different cultivation modes, fermentation and separation processes, will be summarized and discussed. The future prospects and perspectives of microbial menaquinone production will also be discussed finally.

Improvement of menaquinone-7 production by Bacillus subtilis natto in a novel residue-free medium by increasing the redox potential

Bacillus subtilis natto is a GRAS bacterium. Nattokinase, with fibrinolytic and antithrombotic activities, is one of the major products of this organism. It is being gradually recognized that B. subtilis natto can also be used as a biosynthetic strain for vitamin K2, which has phenomenal benefits, such as effects in the prevention of cardiovascular diseases and osteoporosis along with antitumor effects. Knocking out of the aprN gene by homologous recombination could improve the redox potential and slightly increase the concentration of MK-7. By detecting the change in redox potential during the growth of B. subtilis natto, a good oxygen supply and state of the cell membrane were found to be beneficial to vitamin K2 synthesis. A two-step RSM was used to optimize the operation parameters and substrate concentration in the new residue-free fermentation culture. The optimal conditions for the residue-free medium and control were determined. The optimum concentrations of soybean flour, corn flour, and peptone were 78.9, 72.4, and 24.8 g/L, respectively. The optimum rotational speed and volume of the culture medium using a shaking flask were 117 rpm and 10%, respectively. The state and composition of the cell membranes were more stable when engineered bacteria were cultured in this residue-free fermentation medium. Finally, the concentration of MK-7 increased by 37% to 18.9 mg/L, and the fermentation time was shortened by 24 h.

Biofilm reactors as a promising method for vitamin K (menaquinone-7) production

Menaquinone-7 (MK-7) is the most potent subtype of vitamin K with extraordinarily high half-life in the circulatory system. Therefore, MK-7 plays a critical role in promoting human wellbeing today. Studies on MK-7 every year show more and more magnificent benefits of it in preventing cardiovascular diseases and osteoporosis to battling cancer cells, Alzheimer's and Parkinson's diseases. Thus, it needs to be supplemented to daily diet for accumulative and long-term benefits. Chemical synthesis of MK-7 produces a significant cis-isomer form of it, which has no biological activity. Fortunately, due to its key role in electron transfer in bacteria, trans-MK-7 is biosynthesized by especially Gram-positive strains mainly Bacillus genus. Concordantly, MK-7 could be produced via solid or liquid state fermentation strategies. In either regime, when static fermentation is applied in the absence of agitation and aeration, operational issues arise such as heat and mass transfer inefficiencies. Thus, scaling up the process becomes a challenge. On the other hand, studies have indicated that biofilm and pellicle formation that occur in static fermentations are key characteristics for extracellular MK-7 secretion. Therefore, this review covers the most recent discoveries of the therapeutic properties of MK-7 and optimization attempts at increasing its biosynthesis in different media compositions and effective growth parameters as well as the cutting-edge use of biofilm reactors where B. subtilis cells have the infrastructures to form mature biofilm formations on plastic composite supports. Biofilm reactors therefore can provide robust extracellular MK-7 secretion while simultaneously enduring high agitation and aeration rates, which then address the scale-up and operational issues associated with static fermentation strategies.