Enhanced production of recombinant nattokinase in Bacillus subtilis by the elimination of limiting factors

Microbial nattokinase: from synthesis to potential application

Nattokinase (NK) is an alkaline serine protease with strong thrombolytic activity produced by Bacillus spp. or Pseudomonas spp. It is a potential therapeutic agent for thrombotic diseases because of its safety, economy, and lack of side effects. Herein, a comprehensive summary and analysis of the reports surrounding NK were presented, and the physical-chemical properties and producers of NK were first described. The process and mechanism of NK synthesis were summarized, but these are vague and not specific enough. Further results may be achieved if detection techniques such as multi-omics are used to explore the process of NK synthesis. The purification of NK has problems such as a complicated operation and low recovery rate, which were found when summarizing the techniques to improve the quality of finished products. If multiple simple and efficient precipitation methods and purification materials are combined to purify NK, it may be possible to solve the current challenges. Additionally, the application potential of NK in biomedicine was reviewed, but functional foods with NK are challenging for acceptance in daily life due to their unpleasant odor. Accordingly, multi-strain combination fermentation or food flavoring agents can improve the odor of fermented foods and increase people's acceptance of them. Finally, the possible future directions focused on NK studies were proposed and provided suggestions for subsequent researchers.

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.

Heterologous expression of nattokinase from B. subtilis natto using Pichia pastoris GS115 and assessment of its thrombolytic activity

Background

Nattokinase is a fibrinolytic enzyme that has huge market value as a nutritional supplement for health promotion. In order to increase nattokinase yields, fermentation conditions, strains, cultivation media, and feeding strategies have been optimized. Nattokinase has been expressed using several heterologous expression systems. Pichia pastoris heterologous expression system was the alternative.

Results

This report aimed to express high levels of nattokinase from B. subtilis natto (NK-Bs) using a Pichia pastoris heterologous expression system and assess its fibrinolytic activity in vivo. Multicopy expression strains bearing 1–7 copies of the aprN gene were constructed. The expression level of the target protein reached a maximum at five copies of the target gene. However, multicopy expression strains were not stable in shake-flask or high-density fermentation, causing significant differences in the yield of the target protein among batches. Therefore, P. pastoris bearing a single copy of aprN was used in shake-flask and high-density fermentation. Target protein yield was 320 mg/L in shake-flask fermentation and approximately 9.5 g/L in high-density fermentation. The recombinant nattokinase showed high thermo- and pH-stability. The present study also demonstrated that recombinant NK-Bs had obvious thrombolytic activity.

Conclusions

This study suggests that the P. pastoris expression system is an ideal platform for the large-scale, low-cost preparation of nattokinase.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12896-021-00708-4.

Study on the mechanism of production of γ-PGA and nattokinase in Bacillus subtilis natto based on RNA-seq analysis

Poly-γ-glutamic acid (γ-PGA) and nattokinase (NK) are the main substances produced by Bacillus subtilis natto in solid-state fermentation and have wide application prospects. We found that our strains had higher activity of nattokinase when soybeans were used as substrate to increase the yield of γ-PGA. Commercial production of γ-PGA and nattokinase requires an understanding of the mechanism of co-production. Here, we obtained the maximum γ-PGA yield (358.5 g/kg, w/w) and highest activity of NK during fermentation and analyzed the transcriptome of Bacillus subtilis natto during co-production of γ-PGA and NK. By comparing changes in expression of genes encoding key enzymes and the metabolic pathways associated with the products in genetic engineering, the mechanism of co-production of γ-PGA and nattokinase can be summarized based on RNA-seq analysis. This study firstly provides new insights into the mechanism of co-production of γ-PGA and nattokinase by Bacillus subtilis natto and reveals potential molecular targets to promote the co-production of γ-PGA and nattokinase.

Non-sterile Submerged Fermentation of Fibrinolytic Enzyme by Marine Bacillus subtilis Harboring Antibacterial Activity With Starvation Strategy

Microbial fibrinolytic enzyme is a promising candidate for thrombolytic therapy. Non-sterile production of fibrinolytic enzyme by marine Bacillus subtilis D21-8 under submerged fermentation was realized at a mild temperature of 34°C, using a unique combination of starvation strategy and self-production of antibacterial agents. A medium composed of 18.5 g/L glucose, 6.3 g/L yeast extract, 7.9 g/L tryptone, and 5 g/L NaCl was achieved by conventional and statistical methods. Results showed efficient synthesis of fibrinolytic enzyme and antibacterial compounds required the presence of both yeast extract and tryptone in the medium. At shake-flask level, the non-sterile optimized medium resulted in higher productivity of fibrinolytic enzyme than the sterile one, with an enhanced yield of 3,129 U/mL and a production cost reduced by 24%. This is the first report dealing with non-sterile submerged fermentation of fibrinolytic enzyme, which may facilitate the development of feasible techniques for non-sterile production of raw materials for the preparation of potential drugs with low operation cost.

Enhancement of a high efficient autoinducible expression system in Bacillus subtilis by promoter engineering

Quorum-sensing related promoter srfA (PsrfA) was used to construct autoinducible expression system for production of recombinant proteins in Bacillus subtilis. PsrfA was prominent in the unique property of inducer-free activity that is closely correlated with cell density. Here, using green fluorescent protein (GFP) as the reporter protein, PsrfA was optimized by shortening its sequences and changing the nucleotides at the conserved regions of -35 -15 and -10 regions, obtaining a library of PsrfA derivatives varied in the strength of GFP production. Among all the promoter mutants, the strongest promoter P10 was selected and the strength in GFP expression was 150% higher than that of PsrfA. Heterologous protein of aminopeptidase and nattokinase could be overexpressed by P10, the activities of which were 360% and 50% higher than that of PsrfA, respectively. These results suggested that the enhanced promoter P10 could be used to develop autoinducible expression system for overexpression of heterologous proteins in B. subtilis.

Cloning and enhancing production of a detergent- and organic-solvent-resistant nattokinase from Bacillus subtilis VTCC-DVN-12-01 by using an eight-protease-gene-deficient Bacillus subtilis WB800

Background

Nattokinases/Subtilisins (EC 3.4.21.62) belong to the second large family of serine proteases, which gain significant attention and play important role in many biotechnology processes. Thus, a number of nattokinases/subtilisins from various Bacillus species, especially from B. subtilis strains, extensively have been investigated to understand their biochemical and physical properties as well as to improve the production for industrial application. The purpose of this study was to clone a nattokinase gene from Bacillus subtilis strain VTCC-DVN-12-01, enhance its production in B. subtilis WB800, which is deficient in eight extracellular proteases and characterize its physicochemical properties for potential application in organic synthesis and detergent production.

Results

A gene coding for the nattokinase (Nk) from B. subtilis strain VTCC-DVN-12-01 consisted of an ORF of 1146 nucleotides, encoding a pre-pro-protein enzyme (30-aa pre-signal peptide, 76-aa pro-peptide and 275-aa mature protein with a predicted molecular mass of 27.7 kDa and pI 6.6). The nattokinase showed 98-99% identity with other nattokinases/subtilisins from B. subtilis strains in GenBank. Nk was expressed in B. subtilis WB800 under the control of acoA promoter at a high level of 600 mg protein per liter culture medium which is highest yield of proteins expressed in any extracellular-protease-deficient B. subtilis system till date. Nk was purified to homogeneity with 3.25 fold purification, a specific activity of 12.7 U/mg, and a recovery of 54.17%. The purified Nk was identified by MALDI-TOF mass spectrometry through three peptides, which showed 100% identity to corresponding peptides of the B. subtilis nattokinase (CAC41625). An optimal activity for Nk was observed at 65°C and pH 9. The nattokinase was stable at temperature up to 50°C and in pH range of 5–11 and retained more than 85% of its initial activity after incubation for 1 h. Mg²⁺ activated Nk up to 162% of its activity. The addition of Triton X-100, Tween 20, and Tween 80 showed an activation of Nk up to 141% of its initial activity but SDS strongly inhibited. The enzyme was highly resistant to organic solvents.

Conclusions

Our findings demonstrated that an eight-protease-gene-deficient Bacillus subtilis WB800 could overproduce the nattokinase from B. subtilis VTCC-DVN-12-01. Due to high resistance to detergents and organic solvents of this nattokinase, it could be potentially applied in organic synthesis and detergent production.

Production of nattokinase by batch and fed-batch culture of Bacillus subtilis

Nattokinase was produced by batch and fed-batch culture of Bacillus subtilis in flask and fermentor. Effect of supplementing complex media (peptone, yeast extract, or tryptone) was investigated on the production of nattokinase. In flask culture, the highest cell growth and nattokinase activity were obtained with 50 g/L of peptone supplementation. In this condition, nattokinase activity was 630 unit/ml at 12 h. In batch culture of B. subtilis in fermentor, the highest nattokinase activity of 3400 unit/ml was obtained at 10h with 50 g/L of peptone supplementation. From the batch kinetics data, it was shown that nattokinase production was growth-associated and culture should be harvested before stationary phase for maximum nattokinase production. In fed-batch culture of B. subtilis using pH-stat feeding strategy, cell growth (optical density monitored at 600 nm) increased to ca. 100 at 22 h, which was 2.5 times higher than that in batch culture. The highest nattokinase activity was 7100 unit/ml at 19 h, which was also 2.1 times higher than that in batch culture.