Functional membrane microdomains (FMMs) that are mainly composed of scaffold proteins and polyisoprenoids play important roles in diverse cellular physiological processes in bacteria. The aim of this study was to identify the correlation between MK-7 and FMMs and then regulate the MK-7 biosynthesis through FMMs. Firstly, the relationship between FMMs and MK-7 on the cell membrane was determined by fluorescent labeling. Secondly, we demonstrated that MK-7 is a key polyisoprenoid component of FMMs by analyzing the changes in the content of MK-7 on cell membrane and the changes in the membrane order before and after destroying the integrity of FMMs. Subsequently, the subcellular localization of some key enzymes in MK-7 synthesis was explored by visual analysis, and the intracellular free pathway enzymes Fni, IspA, HepT and YuxO were localized to FMMs through FloA to achieve the compartmentalization of MK-7 synthesis pathway. Finally, a high MK-7 production strain BS3AT was successfully obtained. The production of MK-7 reached 300.3 mg/L in shake flask and 464.2 mg/L in 3 L fermenter.
Bacillus subtilis/metabolism* ; Vitamin K 2/metabolism* ; Bioreactors/microbiology* ; Membrane Microdomains/metabolism*

Bacillus subtilis is recognized as a generally-regarded-as-safe strain, and has been widely used in the biosynthesis of high value-added products, including N-acetylneuraminic acid (NeuAc) which is widely used as a nutraceutical and a pharmaceutical intermediate. Biosensors responding to target products are widely used in dynamic regulation and high-throughput screening in metabolic engineering to improve the efficiency of biosynthesis. However, B. subtilis lacks biosensors that can efficiently respond to NeuAc. This study first tested and optimized the transport capacity of NeuAc transporters, and obtained a series of strains with different transport capacities for testing NeuAc-responsive biosensors. Subsequently, the binding site sequence of Bbr_NanR responding to NeuAc was inserted into different sites of the constitutive promoter of B. subtilis, and active hybrid promoters were obtained. Next, by introducing and optimizing the expression of Bbr_NanR in B. subtilis with NeuAc transport capacity, we obtained an NeuAc-responsive biosensor with wide dynamic range and higher activation fold. Among them, P535-N2 can sensitively respond to changes in intracellular NeuAc concentration, with the largest dynamic range (180-20 245) AU/OD. P566-N2 shows a 122-fold of activation, which is 2 times of the reported NeuAc-responsive biosensor in B. subtilis. The NeuAc-responsive biosensor developed in this study can be used to screen enzyme mutants and B. subtilis strains with high NeuAc production efficiency, providing an efficient and sensitive analysis and regulation tool for biosynthesis of NeuAc in B. subtilis.
N-Acetylneuraminic Acid/metabolism* ; Bacillus subtilis/metabolism* ; Promoter Regions, Genetic/genetics* ; Binding Sites ; Biosensing Techniques

Engineered probiotics can serve as therapeutics based on their ability of produce recombinant immune-stimulating properties. In this study, we built the recombinant Bacillus subtilis WB800 expressing antimicrobial peptide KR32 (WB800-KR32) using genetic engineering methods and investigated its protective effects of nuclear factor-E2-related factor 2 (Nrf2)‍-Kelch-like ECH-associated protein 1 (Keap1) pathway activation in intestinal oxidative disturbance induced by enterotoxigenic Escherichia coli (ETEC) K88 in weaned piglets. Twenty-eight weaned piglets were randomly distributed into four treatment groups with seven replicates fed with a basal diet. The feed of the control group (CON) was infused with normal sterilized saline; meanwhile, the ETEC, ETEC+WB800, and ETEC+WB800-KR32 groups were orally administered normal sterilized saline, 5×10¹⁰ CFU (CFU: colony forming units) WB800, and 5×10¹⁰ CFU WB800-KR32, respectively, on Days 1‍‒‍14 and all infused with ETEC K88 1×10¹⁰ CFU on Days 15‍‒‍17. The results showed that pretreatment with WB800-KR32 attenuated ETEC-induced intestinal disturbance, improved the mucosal activity of antioxidant enzyme (catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx)) and decreased the content of malondialdehyde (MDA). More importantly, WB800-KR32 downregulated genes involved in antioxidant defense (GPx and SOD1). Interestingly, WB800-KR32 upregulated the protein expression of Nrf2 and downregulated the protein expression of Keap1 in the ileum. WB800-KR32 markedly changed the richness estimators (Ace and Chao) of gut microbiota and increased the abundance of Eubacterium_rectale_ATCC_33656 in the feces. The results suggested that WB800-KR32 may alleviate ETEC-induced intestinal oxidative injury through the Nrf2-Keap1 pathway, providing a new perspective for WB800-KR32 as potential therapeutics to regulate intestinal oxidative disturbance in ETEC K88 infection.
Animals ; Swine ; Enterotoxigenic Escherichia coli ; Kelch-Like ECH-Associated Protein 1 ; Bacillus subtilis ; NF-E2-Related Factor 2 ; Antioxidants ; Oxidative Stress

L-asparaginase (L-ASN) is widely applied in the treatment of malignant tumor and low-acrylamide food production, however, the low expression level hampers its application. Heterologous expression is an effective strategy to increase the expression level of target enzymes, and Bacillus is generally used as the host for efficient production of enzymes. In this study, the expression level of L-asparaginase in Bacillus was enhanced through optimization of expression element and host. Firstly, five signal peptides (SP_SacC, SP_AmyL, SP_AprE, SP_YwbN and SP_WapA) were screened, among which SP_SacC showed the best performance, reaching an activity of 157.61 U/mL. Subsequently, four strong promoters (P43, P_ykzA-P43, P_Ubay and P_bacA) from Bacillus were screened, and tandem promoter P_ykzA-P43 showed the highest yield of L-asparaginase, which was 52.94% higher than that of control strain. Finally, three Bacillus expression hosts (B. licheniformis Δ0F3 and BL10, B. subtilis WB800) were investigated, and the maximum L-asparaginase activity, 438.3 U/mL, was reached by B. licheniformis BL10, which was an 81.83% increase compared with that of the control. This is also the highest level of L-asparaginase in shake flask reported to date. Taken together, this study constructed a B. licheniformis strain BL10/P_ykzA-P43-SP_SacC-ansZ capable of efficiently producing L-asparaginase, which laid the foundation for industrial production of L-asparaginase.
Bacillus licheniformis/metabolism* ; Asparaginase/genetics* ; Bacillus/genetics* ; Protein Sorting Signals ; Promoter Regions, Genetic/genetics* ; Bacillus subtilis/genetics* ; Bacterial Proteins

In summer in 2020, Pinellia ternata in many planting areas in Hubei suffered from serious southern blight, as manifested by the yellowing and wilted leaves and rotten tubers. This study aims to identify the pathogen, clarify the biological characteristics of the pathogen, and screen fungicides. To be specific, the pathogen was isolated, purified, and identified, and the pathogenicity was detected according to the Koch's postulates. Moreover, the biological characteristics of the pathogen were analyzed. Furthermore, PDA plates and seedlings were used to determine the most effective fungicides. The results showed that the mycelia of the pathogen were white and villous with silk luster, which produced a large number of white to black brown sclerotia. The pathogen was identified as Athelia rolfsii by morphological observation and molecular identification based on LSU and TEF gene sequences. The optimum growth conditions for A. rolfsii were 30 ℃ and pH 5-8, and the optimum conditions for the germination of sclerotia were 25 ℃ and pH 7-9. Bacillus subtilis, difenoconazole, and flusilazole were identified as effective fungicides with PDA, and their half maximal effective concentration(EC_(50)) was all less than 5 mg·L~(-1). The effective fungicides screened with the seedlings were hymexazol and difenoconazole. Based on the screening experiments, difenoconazole can be used as the main agent for the prevention and treatment of southern blight.
Pinellia/genetics* ; Fungicides, Industrial/pharmacology* ; Seedlings ; Bacillus subtilis ; Mycelium

Bacillus spp. are probiotics and can secrete a variety of natural antimicrobiol active substances, of which lipopeptides are an important class. Up to now, about 90 lipopeptides have been identified, and most of them are cyclic lipopeptides. surfactin, iturin, fengycin, bacillomycin and polymyxins are widely studied, and the first three have huge potential for application due to their properties of surfactants and anti-fungal, anti-bacterial, anti-viral, anti-tumor and anti-inflammatory functions. In this paper, the research progress in the structure, function, synthesis regulation, separation, purification and production of surfactin, iturin and fengycin was reviewed. Synthetic biology is a vital means to increase the yield of lipopeptides, and in the future, lipopeptides can be used in crop cultivation, animal farming, food, medicine and petroleum industries as well as environmental protection. Future research should be strengthened on the discovery of new lipopeptides, synthesis of high-activity lipopeptides, economical production of lipopeptides on a large scale and their safety evaluation.
Anti-Bacterial Agents ; Anti-Infective Agents/pharmacology* ; Bacillus ; Bacillus subtilis ; Lipopeptides/pharmacology* ; Peptides, Cyclic/pharmacology*

Aims: Palm kernel cake (PKC) is a high-protein, high-energy food that is widely utilized in the animal feed business. However, the high fibre and limited amino acid content of untreated PKC were the main issues for it to be used as animal feed, particularly in non-ruminants. To improve the quality of PKC, this study combined the use of solid-state fermentation (SSF) and consortia of fungi and bacteria to treat the PKC. Methodology and results: Two fungi, Emericella nidulans (4DP5) and Cladosporium herbarum (7DF12) and three strains of bacteria, Bacillus subtilis, which were active mannanase producers, were used in different combinations to reduce the hemicellulose content and improve the crude protein content of PKC in a lab-scale solid-state fermentation. PKC inoculated separately with five types of mixed culture treatments were allowed to ferment. The fermentation conditions were 20% inoculum (w/v), 85-92% humidity, pH 7.0 and PKC particle size 0.8 mm. PKC treatments with two fungi, E. nidulans (4DP5) and C. herbarum (7DF12), as well as a fungus-bacterium combination, E. nidulans (4DP5) and B. subtilis, outperformed the other three treatments. The crude protein levels were increased by 3.34% and 1.86%, respectively, due to these treatments. Furthermore, the level of aflatoxins produced increased marginally but remained within the permissible limits. Conclusion, significance and impact of study The treated PKC has more sugar and crude protein and less than 20 parts per billion (ppb) of aflatoxin, making it appropriate for animal consumption. The SSF technique of combining fungi and Bacilli enhanced the nutritional and market value of PKC substantially, which can be upscaled.
Aspergillus nidulans ; Cladosporium ; Bacillus subtilis ; Palm Oil ; Fermentation

L-asparaginase hydrolyzes L-asparagine to produce L-aspartic acid and ammonia. It is widely distributed in microorganisms, plants and serum of some rodents, and has important applications in the pharmaceutical and food industries. However, the poor thermal stability, low catalytic efficiency and low yield hampered the further application of L-asparaginase. In this paper, rational design and 5' untranslated region (5'UTR) design strategies were used to increase the specific enzyme activity and protein expression of L-asparaginase derived from Rhizomucor miehei (RmAsnase). The results showed that among the six mutants constructed through homology modeling combined with sequence alignment, the specific enzyme activity of the mutant A344E was 1.5 times higher than the wild type. Subsequently, a food-safe strain Bacillus subtilis 168/pMA5-A344E was constructed, and the UTR strategy was used for the construction of recombinant strain B. subtilis 168/pMA5 UTR-A344E. The enzyme activity of B. subtilis 168/pMA5 UTR-A344E was 7.2 times higher than that of B. subtilis 168/pMA5-A344E. The recombinant strain B. subtilis 168/pMA5 UTR-A344E was scaled up in 5 L fermenter, and the final yield of L-asparaginase was 489.1 U/mL, showing great potential for industrial application.
Asparaginase/genetics* ; Bacillus subtilis/genetics* ; Industrial Microbiology ; Protein Engineering ; Rhizomucor/enzymology* ; Sequence Alignment

D-allulose-3-epimerase (DPEase) is the key enzyme for isomerization of D-fructose to D-allulose. In order to improve its thermal stability, short amphiphilic peptides (SAP) were fused to the N-terminal of DPEase. SDS-PAGE analysis showed that the heterologously expressed DPEase folded correctly in Bacillus subtilis, and the protein size was 33 kDa. After incubation at 40 °C for 48 h, the residual enzyme activity of SAP1-DSDPEase was 58%. To make the recombinant B. subtilis strain reusable, cells were immobilized with a composite carrier of sodium alginate (SA) and titanium dioxide (TiO2). The results showed that 2% SA, 2% CaCl2, 0.03% glutaraldehyde solution and a ratio of TiO2 to SA of 1:4 were optimal for immobilization. Under these conditions, up to 82% of the activity of immobilized cells could be retained. Compared with free cells, the optimal reaction temperature of immobilized cells remained unchanged at 80 °C but the thermal stability improved. After 10 consecutive cycles, the mechanical strength remained unchanged, while 58% of the enzyme activity could be retained, with a conversion rate of 28.8% achieved. This study demonstrated a simple approach for using SAPs to improve the thermal stability of recombinant enzymes. Moreover, addition of TiO2 into SA during immobilization was demonstrated to increase the mechanical strength and reduce cell leakage.
Bacillus subtilis/metabolism* ; Carbohydrate Epimerases/genetics* ; Enzyme Stability ; Enzymes, Immobilized/metabolism* ; Fructose ; Hydrogen-Ion Concentration ; Racemases and Epimerases ; Temperature

Biosynthesis of nanomaterials has attracted much attention for its excellent characteristics such as low energy consumption, high safety, and environmental friendliness. As we all know, the toxic selenite can be transformed into higher-value nanomaterials by using bacteria. In this study, nano-selenium was synthesized by halophilic Bacillus subtilis subspecies stercoris strain XP in LB medium supplemented with selenite (electron acceptor). The physicochemical characteristics of nano-selenium were analyzed by scanning electron microscope (SEM), X-ray energy dispersive spectral analysis (EDAX), X-ray diffraction (XRD), and fourier transform infrared spectroscopy (FTIR). Meanwhile, the antifungal activity of nano-selenium to strawberry pathogens (fusarium wilt, erythema, and purple spot fungi) was determined. The products from reduction of selenite by strain XP was amorphous spherical selenium nanoparticles (SeNPs) with a diameter range of 135-165 nm. The production of SeNPs was positively correlated with time (0-48 h) and no changes were observed on cell morphology. Selenium was dominant in the surface of SeNPs where the organic elements (C, O, N, and S) existed at the same time. SeNPs were coated with biomolecules containing functional groups (such as -OH, C=O, N-H, and C-H) which were associated with the stability and bioactivity of particles. Although the highest concentration of SeNPs had significant (P<0.05) inhibitory effects on three strains of strawberry pathogens, antifungal activity to erythema and fusarium wilt pathogenic fungi was higher than that to purple spot pathogenic fungi from strawberry. In conclusion, strain XP not only has strong tolerance to high salt stress, but can be also used to synthesize biological SeNPs with good stability and biological activity. Thus, the strain XP has bright perspectives and great potential advantage in pathogens control and green selenium-rich strawberry planting as well as other fields.
Bacillus subtilis ; Fragaria ; Nanoparticles ; Selenious Acid ; Selenium