Development of menaquinone-7 enriched nutraceutical: inside into medium engineering and process modeling

A bioprocess optimization study to enhance the production of Menaquinone-7 using Bacillus subtilis MM26

BACKGROUND

Menaquinone-7 (MK-7) has a vital significance in promoting human health and tackling several global health concerns which makes its production extremely important. MK-7 is not easily accessible at a reasonable cost due to the poor fermentation yields and the existence of several laborious downstream unit processes. Efficient manufacturing methods are essential to meet the global requirements due to the increasing demand in the pharmaceutical and nutraceutical industries. This research study focuses on the enhanced production of MK-7 from Bacillus subtilis MM26 isolated from fermented home-made wine.

RESULTS

A suitable MK-7 production medium for Bacillus subtilis MM26 was determined and the yield was found to be 67 ± 0.6 mg/L. The one factor at a time (OFAT) results showed that medium containing lactose, glycine, with a pH 7, a temperature of 37 °C, and an inoculum size of 2.5% (2 × 10⁶ CFU/mL) was optimal synthesis of MK-7. RSM indicated that incubation time, carbon and nitrogen sources were the factors significantly affecting the MK-7 yield. RSM predicted optimal conditions, which yielded a maximum concentration of 442 ± 2.08 mg/L of MK-7.

CONCLUSIONS

The outcomes of this study demonstrated the potential of Bacillus subtilis MM26 in large-scale industrial production of MK-7. The yield of MK-7 was amplified efficiently by integration of OFAT and RSM, paving the way for cost-efficient industrial production.

A Novel Fast HPLC-UV Method for Menaquinone-7 Determination in Fermentation Broth

Menaquinone-7 (MK-7) plays a key role in bone and cardiovascular health, and it is often included in multivitamin supplements and functional foods. The aim of this study is the development and validation, according to ICH guidelines, of a fast, highly sensitive, and reliable reverse-phase HPLC-UV quantification of vitamin K2 as MK-7 in a common biological matrix sample, such as fermentation broth medium from Bacillus subtilis, with the advantage of single-step extraction and short analysis time. MK-7 was successfully isolated from the fermentation broth and its interfering residues by thermo-acidic extraction using 5% H2SO4 and ethanol, without derivatization, and was retained using a C8 column. The isocratic elution and UV detection at 268 nm within a 3-min run time allowed quantification over a wide accuracy range of 0.10-18.00 μg/mL, with an LOQ value of 0.10 μg/mL and an LOD value of 0.03 μg/mL. The method was found to be precise, accurate, and reliable, with RSD% lower than 5% and recoveries varying between 96.0% and 108.9%. The proposed method unlocks the opportunity to be suitable for routine analysis in the screening of bacterial strains producing MK-7, as well as to be successfully employed in manufacturing processes in the nutraceutical and food industries where complex matrices are involved.

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.

The Impact of Amine-Functionalised Iron Oxide Nanoparticles on the Menaquinone-7 Isomer Profile and Production of the Bioactive Isomer

The K family of vitamins includes a collection of molecules with different pharmacokinetic characteristics. Menaquinone-7 (MK-7) has the finest properties and is the most therapeutically beneficial due to its long plasma half-life and outstanding extrahepatic bioavailability. MK-7 exhibits cis-trans isomerism, and merely the all-trans form is biologically efficacious. Therefore, the remedial value of MK-7 end products is exclusively governed by the quantity of all-trans MK-7. Consumers favour fermentation for the production of MK-7; however, it involves several challenges. The low MK-7 yield and extensive downstream processing requirements increase production costs, resulting in an expensive final product that is not universally available. Bacterial cell immobilisation with iron oxide nanoparticles (IONs) can potentially address the limitations of MK-7 fermentation. Uncoated IONs tend to have low stability and can adversely affect cell viability; thus, amine-functionalised IONs, owing to their increased physicochemical stability and biocompatibility, are a favourable alternative. Nonetheless, employing biocompatible IONs for this purpose is only advantageous if the bioactive MK-7 isomer is obtained in the most significant fraction, exploring which formed the aim of this investigation. Two amine-functionalised IONs, namely 3-aminopropyltriethoxysilane (APTES)-coated IONs (IONs@APTES) and L-Lysine (L-Lys)-coated IONs (L-Lys@IONs), were synthesised and characterised, and their impact on various parameters was evaluated. IONs@APTES were superior, and the optimal concentration (300 μ g/mL) increased all-trans MK-7 production and improved its yield relative to the untreated cells by 2.3- and 3.1-fold, respectively. The outcomes of this study present an opportunity to develop an innovative and effective fermentation method that enhances the production of bioactive MK-7.

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.

Fermented soybean foods: A review of their functional components, mechanism of action and factors influencing their health benefits

After thousands of years of evolution and development, traditional fermented soybean foods, with their unique charm, have gained a stable place in the global market. With the explosive development of modern biological technologies, some traditional fermented soybean foods that possess health-promoting benefits are gradually appearing. Physiologically active substances in fermented soybean foods have received extensive attention in recent decades. This review addresses the potential health benefits of several representative fermented soybean foods, as well as the action mechanism and influencing factors of their functional components. Phenolic compounds, low-molecular-weight peptides, melanoidins, furanones and 3-hydroxyanthranilic acid are the antioxidative components predominantly found in fermented soybean foods. Angiotensin I-converting enzyme inhibitory peptides and γ-aminobutyric acid isolated from fermented soy foods provide potential selectivity for hypertension therapy. The potential anti-inflammatory bioactive components in fermented soybean foods include γ-linolenic acid, butyric acid, soy sauce polysaccharides, 2S albumin and isoflavone glycones. Deoxynojirimycin, genistein, and betaine possess high activity against α-glucosidase. Additionally, fermented soybean foods contain neuroprotective constituents, including indole alkaloids, nattokinase, arbutin, and isoflavone vitamin B12. The anticancer activities of fermented soybean foods are associated with surfactin, isolavone, furanones, trypsin inhibitors, and 3-hydroxyanthranilic acid. Nattokinase is highly correlated with antioxidant activity. And a high level of menaquinones-7 is linked to protection against neurodegenerative diseases. Sufficiently recognizing and exploiting the health benefits and functional components of traditional fermented soybean foods could provide a new strategy in the development of the food fermentation industry.

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.

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.

Modern Methods of Pre-Treatment of Plant Material for the Extraction of Bioactive Compounds

In this review, recent advances in the methods of pre-treatment of plant material for the extraction of secondary metabolites with high biological activity are presented. The correct preparation of the material for extraction is as important as the selection of the extraction method. This step should prevent the degradation of bioactive compounds as well as the development of fungi and bacteria. Currently, the methods of preparation are expected to modify the particles of the plant material in such a way that will contribute to the release of bioactive compounds loosely bonded to cell wall polymers. This review presents a wide range of methods of preparing plant material, including drying, freeze-drying, convection drying, microwave vacuum drying, enzymatic processes, and fermentation. The influence of the particular methods on the structure of plant material particles, the level of preserved bioactive compounds, and the possibility of their release during the extraction were highlighted. The plant material pre-treatment techniques used were discussed with respect to the amount of compounds released during extraction as well their application in various industries interested in products with a high content of biologically active compounds, such as the pharmaceutical, cosmetics, and food industries.

Highly Efficient Production of Menaquinone-7 from Glucose by Metabolically Engineered Escherichia coli

Menaquinone-7 (MK-7) possesses wide health and medical value, and the market demand for MK-7 has increased. Metabolic engineering for MK-7 production in Escherichia coli still remains challenging due to the characteristics of the competing quinone synthesis, and cells mainly synthesized menaquinones under anaerobic conditions. To increase the production of MK-7 in engineered E. coli strains under aerobic conditions, we divided the whole MK-7 biosynthetic pathway into three modules (MVA pathway, DHNA pathway, and MK-7 pathway) and systematically optimized each of them. First, by screening and enhancing Idi expression, the amounts of MK-7/DMK-7 increased significantly. Then, in the MK-7 pathway, by combinatorial overexpression of endogenous MenA and exogenous UbiE, and fine-tuning the expression of HepPPS, MenA, and UbiE, 70 μM MK-7 was achieved. Third, the DHNA synthetic pathway was enhanced, and 157 μM MK-7 was achieved. By the combinational metabolic engineering strategies and membrane engineering, an efficient metabolic engineered E. coli strain for MK-7 synthesis was developed, and 200 μM (129 mg/L) MK-7 was obtained in shake flask experiment, representing a 306-fold increase compared to the starting strain. In the scale-up fermentation, 2074 μM (1350 mg/L) MK-7 was achieved after 52 h fermentation with a productivity of 26 mg/L/h. This is the highest titer of MK-7 ever reported. This study offers an alternative method for MK-7 production from biorenewable feedstock (glucose) by engineered E. coli. The high titer of our process should make it a promising cost-effective resource for MK-7.

Tetramethylpyrazine from adlay (Coix lacryma-jobi) biotransformation by Bacillus subtilis and its quality characteristics

Adlay, as a traditional Chinese medicine, has been used in nourishing foods, which are rich in a variety of nutrients (special biological compounds). The study was designed to optimize the fermentation parameters of dehulled, polished and broken adlay fermented by Bacillus subtilis BJ3-2 with regard to tetramethylpyrazine (TMP) yield and fibrinolytic enzyme activity. Then the proximate and bioactive components of B. subtilis-fermented adlay were evaluated. Box-Behnken design results showed that the TMP yield was 6.93 mg/g DW (dried weight) of B. subtilis-fermented polished adlay, which was about 136 times higher than that of B. subtilis-fermented soybean (BSB). The fibrinolytic enzyme activity was 2236.17 U/g in B. subtilis-fermented dehulled adlay, and slightly less than in BSB. B. subtilis-fermented adlay contained higher fat, free amino acids and fatty acids contents but lower protein and starch contents than raw adlay. Except for coixol and coixan, the levels of γ-aminobutyric acid, triterpenes, phenolics, flavonoids and coixenolide in B. subtilis-fermented adlay increased by 14.05, 2.02, 2.31 and 1.36 times, respectively. The contents of phenolic acids including caffeic, gallic, catechinic and chlonogenic acids in the free phenolic extracts significantly increased (p < 0.05). The results demonstrated that the biotransformation of high-yield TMP, fibrinolytic enzyme and other bioactive components of B. subtilis-fermented adlay products was realized. B. subtilis-fermented adlay could be a promising value-added food, and that is more suitable for human consumption.

Microbiome and Functional Analysis of a Traditional Food Process: Isolation of a Novel Species (Vibrio hibernica) With Industrial Potential

Traditional food preservation processes are vital for the food industry. They not only preserve a high-quality protein and nutrient source but can also provide important value-added organoleptic properties. The Wiltshire process is a traditional food curing method applied to meat, and special recognition is given to the maintenance of a live rich microflora within the curing brine. We have previously analyzed a curing brine from this traditional meat process and characterized a unique microbial core signature. The characteristic microbial community is actively maintained and includes the genera, Marinilactibacillus, Carnobacterium, Leuconostoc, and Vibrio. The bacteria present are vital for Wiltshire curing compliance. However, the exact function of this microflora is largely unknown. A microbiome profiling of three curing brines was conducted and investigated for functional traits by the robust bioinformatic tool, Tax4Fun. The key objective was to uncover putative metabolic functions associated with the live brine and to identify changes over time. The functional bioinformatic analysis revealed metabolic enrichments over time, with many of the pathways identified as being involved in organoleptic development. The core bacteria present in the brine are Lactic Acid Bacteria (LAB), with the exception of the Vibrio genus. LAB are known for their positive contribution to food processing, however, little work has been conducted on the use of Vibrio species for beneficial processes. The Vibrio genome was sequenced by Illumina MiSeq technologies and annotated in RAST. A phylogenetic reconstruction was completed using both the 16S rRNA gene and housekeeping genes, gapA, ftsZ, mreB, topA, gyrB, pyrH, recA, and rpoA. The isolated Vibrio species was defined as a unique novel species, named Vibrio hibernica strain B1.19. Metabolic profiling revealed that the bacterium has a unique substrate scope in comparison to other closely related Vibrio species tested. The possible function and industrial potential of the strain was investigated using carbohydrate metabolizing profiling under food processing relevant conditions. Vibrio hibernica is capable of metabolizing a unique carbohydrate profile at low temperatures. This characteristic provides new application options for use in the industrial food sector, as well as highlighting the key role of this bacterium in the Wiltshire curing process.

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.

Vitamin K as a Diet Supplement with Impact in Human Health: Current Evidence in Age-Related Diseases

Vitamin K health benefits have been recently widely shown to extend beyond blood homeostasis and implicated in chronic low-grade inflammatory diseases such as cardiovascular disease, osteoarthritis, dementia, cognitive impairment, mobility disability, and frailty. Novel and more efficient nutritional and therapeutic options are urgently needed to lower the burden and the associated health care costs of these age-related diseases. Naturally occurring vitamin K comprise the phylloquinone (vitamin K1), and a series of menaquinones broadly designated as vitamin K2 that differ in source, absorption rates, tissue distribution, bioavailability, and target activity. Although vitamin K1 and K2 sources are mainly dietary, consumer preference for diet supplements is growing, especially when derived from marine resources. The aim of this review is to update the reader regarding the specific contribution and effect of each K1 and K2 vitamers in human health, identify potential methods for its sustainable and cost-efficient production, and novel natural sources of vitamin K and formulations to improve absorption and bioavailability. This new information will contribute to foster the use of vitamin K as a health-promoting supplement, which meets the increasing consumer demand. Simultaneously, relevant information on the clinical context and direct health consequences of vitamin K deficiency focusing in aging and age-related diseases will be discussed.

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.

Engineering a Bifunctional Phr60-Rap60-Spo0A Quorum-Sensing Molecular Switch for Dynamic Fine-Tuning of Menaquinone-7 Synthesis in Bacillus subtilis

Quorum sensing (QS)-based dynamic regulation has been widely used as basic tool for fine-tuning gene expression in response to cell density changes without adding expensive inducers. However, most reported QS systems primarily relied on down-regulation rather than up-regulation of gene expression, significantly limiting its potential as a molecular switch to control metabolic flux. To solve this challenge, we developed a bifunctional and modular Phr60-Rap60-Spo0A QS system, based on two native promoters, P_abrB (down-regulation by Spo0A-P) and P_spoiiA (up-regulation by Spo0A-P). We constructed a library of promoters with different capacities to implement down-regulation and up-regulation by changing the location, number, and sequences of the binding sites for Spo0A-P. The QS system can dynamically balance the relationship between efficient synthesis of the target product and cell growth. Finally, we validated the usefulness of this strategy by dynamic control of menaquinone-7 (MK-7) synthesis in Bacillus subtilis 168, a model Gram-positive bacterium, with the bifunctional Phr60-Rap60-Spo0A quorum sensing system. Our dynamic pathway regulation led to a 40-fold improvement of MK-7 production from 9 to 360 mg/L in shake flasks and 200 mg/L in 15-L bioreactor. Taken together, our bilayer QS system has been successfully integrated with biocatalytic functions to achieve dynamic pathway regulation in B. subtilis 168, which may be extended for use in other microbes to fine-tune gene expression and improve metabolites production.

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.

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

Menaquinone-7 (MK-7) as the most important form of Vitamin K has been reported to have miraculous benefits such as preventing cardiovascular diseases and osteoporosis along with antitumor effects. Therefore, there have been numerous studies in the past decades to improve MK-7 production via microbial fermentation. Unfortunately, both solid and liquid state fermentation strategies that are utilized for MK-7 production, face fundamental operational and scale-up issues as well as intense heat and mass transfer problems during fermentation. In this regard, biofilm reactors seem to be a practical solution to overcome these issues and enhance the production in agitated liquid fermentation. Therefore, this study was undertaken to utilize biofilm reactors in investigating and optimizing different media components in a glycerol-based medium. Using response surface methodology, the effects of glycerol, yeast extract, and soytone were studied in the fermentation medium on MK-7 production in biofilm reactor. With a composition of 48.2 g/L of glycerol, 8.1 g/L of yeast extracts, 13.6 g/L of soytone and 0.06 g/L of K₂HPO₄, MK-7 concentrations could reach 14.7 ± 1.4 mg/L in biofilm reactors, which was 57% higher compared to the MK-7 concentration achieved in suspended-cell reactors under similar conditions, while glycerol was depleted by the end of the fifth day in biofilm reactors, but glycerol was never depleted in suspended-cell reactors. Evidently, biofilm reactors present a reliable strategy to address the operational issues that occur during MK-7 biosynthesis on an industrial scale production.

Implementation of fed-batch strategies for vitamin K (menaquinone-7) production by Bacillus subtilis natto in biofilm reactors

Recent studies show the essential health benefits associated with vitamin K, especially menaquinone-7 (MK-7). These benefits include reducing risks of cardiovascular diseases, osteoporosis, and even cancer. However, MK-7 production on an industrial level is only possible through bacterial fermentation and also current static fermentation strategies are not potent enough with difficulties to scale up. Biofilm reactors, however, may be a practical alternative. Biofilm reactors provide a controlled environment for the microorganisms to form mature and robust biofilms that enable them to produce value-added products with enhanced efficiencies. In this study, fed-batch addition of glucose and glycerol were investigated to the base media in biofilm reactors, as carbon source addition seemed crucial in batch fermentations. Results indicated that fed-batch strategies can be significantly effective in glucose-based medium, increasing the end-product concentrations to 28.7 ± 0.3 mg/L of MK-7 which was 2.3 fold higher than the level produced in suspended-cell bioreactors and renders the biofilm reactors as a potential replacement for static fermentation strategies. Moreover, morphological changes of B. subtilis were tracked during the 12-day long fermentation runs and finally, SEM investigations confirmed significant biofilm and extracellular matrices formed on the plastic composite support (PCS) in the biofilm reactors. In conclusion, biofilm reactors especially with fed-batch fermentation regimes seem to be an effective tool for MK-7 production at industrial scales.

Optimization of Bacillus subtilis natto growth parameters in glycerol-based medium for vitamin K (Menaquinone-7) production in biofilm reactors

Menaquinone-7 (MK-7) is the key form of vitamin K used as a dietary supplement and its production revolves around Bacillus subtilis natto. Current fermentation strategies, which suggest static fermentations without aeration and agitation, can be problematic for large scale MK-7 production due to biofilm formation. The use of biofilm reactors, therefore, is proposed in the present study, which could utilize both agitation and aeration without interrupting MK-7 secretion. In this study, biofilm reactors were constructed using the selected plastic composite support (PCS) and B. subtilis natto strain for MK-7 production. Using response surface methodology (RSM), optimum growth parameters including temperature, pH, and agitation were determined in a glycerol-based medium. Results were presented in a statistical model (R ² = 0.90), leading to optimum growth conditions of temperature (35 °C), agitation (200 rpm) and pH (6.58). Model-predicted MK-7 concentration was validated and MK-7 concentration of 12.09 mg/L was produced in the biofilm reactor. The obtained concentration was 58% higher as compared to the suspended-cell culture (7.67 mg/L). The results of this study will provide a critical step towards improved industrial scale production of MK-7.