Purification and Characterization of a Novel Cold Shock Protein-Like Bacteriocin Synthesized by Bacillus thuringiensis

Impacts of UV radiation on Bacillus biocontrol agents and their resistance mechanisms

Bacillus biocontrol agent(s) BCA(s) such as Bacillus cereus, Bacillus thuringiensis and Bacillus subtilis have been widely applied to control insects' pests of plants and pathogenic microbes, improve plant growth, and facilitate their resistance to environmental stresses. In the last decade, researchers have shown that, the application of Bacillus biocontrol agent(s) BCA(s) optimized agricultural production yield, and reduced disease risks in some crops. However, these bacteria encountered various abiotic stresses, among which ultraviolet (UV) radiation severely decrease their efficiency. Researchers have identified several strategies by which Bacillus biocontrol agents resist the negative effects of UV radiation, including transcriptional response, UV mutagenesis, biochemical and artificial means (addition of protective agents). These strategies are governed by distinct pathways, triggered by UV radiation. Herein, the impact of UV radiation on Bacillus biocontrol agent(s) BCA(s) and their mechanisms of resistance were discussed.

Striving for sustainable biosynthesis: discovery, diversification, and production of antimicrobial drugs in Escherichia coli

New antimicrobials need to be discovered to fight the advance of multidrug-resistant pathogens. A promising approach is the screening for antimicrobial agents naturally produced by living organisms. As an alternative to studying the native producer, it is possible to use genetically tractable microbes as heterologous hosts to aid the discovery process, facilitate product diversification through genetic engineering, and ultimately enable environmentally friendly production. In this mini-review, we summarize the literature from 2017 to 2022 on the application of Escherichia coli and E. coli-based platforms as versatile and powerful systems for the discovery, characterization, and sustainable production of antimicrobials. We highlight recent developments in high-throughput screening methods and genetic engineering approaches that build on the strengths of E. coli as an expression host and that led to the production of antimicrobial compounds. In the last section, we briefly discuss new techniques that have not been applied to discover or engineer antimicrobials yet, but that may be useful for this application in the future.

Three novel leaderless bacteriocins have antimicrobial activity against gram-positive bacteria to serve as promising food biopreservative

BACKGROUND

Due to the detrimental effects of chemical preservatives, there has been an increasing demand for safer, healthier and natural bio-preservatives. Bacteriocins have attracted increasing interest because of their potential as natural bio-preservatives.

RESULTS

We screened a large number of Bacillus thuringiensis strains and isolated one strain (B. thuringiensis P86) with antimicrobial activity against several foodborne pathogens. Three novel leaderless bacteriocins, including thucin A1, thucin A2 and thucin A3, were purified and identified from the culture supernatant of B. thuringiensis P86, whose molecular masses were 5552.02, 5578.07 and 5609.06 Da, respectively. Thucin A1 was then selected as a representative to be tested, and it exhibited potent inhibitory activity against all tested gram-positive bacteria. More importantly, thucin A1 showed stronger antimicrobial activity than nisin A against two important foodborne pathogens Bacillus cereus and Listeria monocytogenes. In addition, thucin A1 exhibited strong acid-base adaptability (pH 2-11), high endurance to heat, good stability to trypsin and pepsin, no hemolysis activity and cytotoxicity, and could effectively inhibit or eliminate Bacillus cereus and Listeria monocytogenes in skim milk.

CONCLUSIONS

Our findings indicate that these novel leaderless bacteriocins are potentially promising food biopreservatives.

Osteoarthritis Can Also Start in the Gut: The Gut-Joint Axis

Background

Osteoarthritis is a common cause of pain and disability with an increasing prevalence among the global population (Hunter and Bierma-Zeinstra in Lancet 393(10182):1745-1759, 2019; Zhang and Jordan in Clinics in Geriatric Medicine 26(3):355-369, 2010). Altered immune responses and low-grade systemic inflammation driven by gut dysbiosis are being increasingly recognized as contributing factors to the pathophysiology of OA (Tan et al. in International Journal of Rheumatic Diseases. https://doi.org/10.1111/1756-185X.14123, 2021; Binvignat et al. in Joint, Bone, Spine 88(5):105203, 2021; Ramasamy et al. in Nutrients 13(4):1272, 2021), which increased the interest in the so-called "gut-joint axis". The various microbiota in the gastrointestinal tract is commonly referred to as the gut microbiome. The gut microbiome is affected by age, sex, and immune system activity as well as medications, environment, and diet (Arumugam in Nature. https://doi.org/10.1038/nature09944, 2011). The microbiome is pivotal to maintain host health and contributes to nutrition, host defense, and immune development (Nishida et al. in Clinical Journal of Gastroenterology 11:1-10, 2018). Alterations in this microbiome can induce dysbiosis, which is associated with many human disease states including allergies, autoimmune disease, diabetes, and cancer (Lin and Zhang in BMC Immunology 18(1):2, 2017). A gut-joint axis is proposed as a link involving the gastrointestinal microbiome, the immune response that it induces, and joint health.

Results

Emerging evidence has shown that there are specific changes in the microbiome that are associated with osteoarthritis, including increased Firmicutes/Bacteroides ratio, Streptococcus spp. prevalence, and local inflammation (Collins in Osteoarthritis and Cartilage. https://doi.org/10.1016/j.joca.2015.03.014, 2015; Rios in Science and Reports. https://doi.org/10.1038/s41598-019-40601-x, 2019; Schott in JCI insight. https://doi.org/10.1172/jci.insight.95997, 2018; Boer et al. in Nature Communications 10:4881, 2019). Both the innate and adaptive immune systems are affected by the gut microbiome and can become dysregulated in dysbiosis which ultimately triggers events associated with joint OA.

Conclusions

The gut is an intriguing and novel target for OA therapy. Dietary modification or supplementation with fiber, probiotics, or prebiotics could provide a positive impact on the gut joint axis.

Biostimulation of Bacteria in Liquid Culture for Identification of New Antimicrobial Compounds

We hypothesized that environmental microbiomes contain a wide range of bacteria that produce yet uncharacterized antimicrobial compounds (AMCs) that can potentially be used to control pathogens. Over 600 bacterial strains were isolated from soil and food compost samples, and 68 biocontrol bacteria with antimicrobial activity were chosen for further studies based on inhibition assays against a wide range of food and plant pathogens. For further characterization of the bioactive compounds, a new method was established that used living pathogens in a liquid culture to stimulate bacteria to produce high amounts of AMCs in bacterial supernatants. A peptide gel electrophoresis microbial inhibition assay was used to concurrently achieve size separation of the antimicrobial peptides. Fifteen potential bioactive peptides were then further characterized by tandem MS, revealing cold-shock proteins and 50S ribosomal proteins. To identify non-peptidic AMCs, bacterial supernatants were analyzed by HPLC followed by GC/MS. Among the 14 identified bioactive compounds, 3-isobutylhexahydropyrrolo[1,2-a]pyrazine-1,4-dione and 2-acetyl-3-methyl-octahydropyrrolo[1,2-a]piperazine-1,4-dione were identified as new AMCs. Our work suggests that antimicrobial compound production in microbes is enhanced when faced with a threat from other microorganisms, and that this approach can rapidly lead to the development of new antimicrobials with the potential for upscaling.

Cationic Clitoria ternatea Seed Peptide as a Potential Novel Bioactive Molecule

BACKGROUND

While several biologics have been reported from different parts of Clitoria ternatea, a herbaceous climber of the family Fabaceae, specific production of cationic peptides other than cyclotides (<3.7 kDa) has barely been investigated or their bioactive potential looked into.

OBJECTIVE

To uncover potential bioactivities and characteristics of novel cationic peptides from C. ternatea seeds.

METHODS

C. ternatea seed cationic peptide purified by simple and cost-effective procedures was analyzed by electrophoresis and mass spectrometry. Antimicrobial efficacy was evaluated against bacterial and fungal pathogens. Antioxidant potential was quantified by in vitro antioxidant assays. Physicochemical characterization and Tandem mass spectrometry were performed.

RESULTS

An 8.5 kDa cationic peptide purified from C. ternatea seeds was active against Candida albicans, Staphylococcus aureus, Aeromonas hydrophila and Escherichia coli at a minimum inhibitory concentration in the range of 8-32 μg/ml. This activity was totally uncompromised at pH 5-8 or after 1 h of heat treatment at 70-80 ºC, but was sensitive to protease treatment. Concentration-dependent free-radical scavenging activity and ferric-reducing capacity demonstrated the antioxidant potential of the peptide. Tandem MS analysis of trypsin-digested peptide based on shotgun proteomics detected matching peptide sequences with one or two cysteine residues but had low sequence coverage (≤17%) to known sequences in the C. ternatea protein database. Taken together, the distinct characteristics of this novel 8.5 kDa peptide clearly distinguishes it from known cyclotides of C. ternatea.

CONCLUSIONS

Insights have been obtained into the functional characteristics of what appears to be a novel cationic peptide from C. ternatea seeds, exhibiting significant antimicrobial and antioxidant activities.

Plant Polysaccharides Modulate Biofilm Formation and Insecticidal Activities of Bacillus thuringiensis Strains

After the biological pesticide Bacillus thuringiensis (Bt) is applied to the field, it has to remain on the surface of plants to have the insecticidal activities against insect pests. Bt can form biofilms on the surface of vegetable leaves, which were rich in polysaccharides. However, the relationship between polysaccharides of the leaves and the biofilm formation as well as the insecticidal activities of Bt is still unknown. Herein, this study focused on the effects of plant polysaccharides pectin and xylan on biofilm formation and the insecticidal activities of Bt strains. By adding pectin, there were 88 Bt strains with strong biofilm formation, 69 strains with weak biofilm formation, and 13 strains without biofilm formation. When xylan was added, 13 Bt strains formed strong biofilms, 98 strains formed weak biofilms, and 59 strains did not form biofilms. This indicated that two plant polysaccharides, especially pectin, modulate the biofilm formation of Bt strains. The ability of pectin to induce biofilm formation was not related to Bt serotypes. Pectin promoted the biofilms formed by Bt cells in the logarithmic growth phase and lysis phase at the air–liquid interface, while it inhibited the biofilms formed by Bt cells in the sporangial phase at the air–liquid interface. The dosage of pectin was positively correlated with the yield of biofilms formed by Bt cells in the logarithmic growth phase or lysis phase at the solid–liquid interfaces. Pectin did not change the free-living growth and the cell motility of Bt strains. Pectin can improve the biocontrol activities of the spore–insecticidal crystal protein mixture of Bt and BtK commercial insecticides, as well as the biofilms formed by the logarithmic growth phase or lysis phase of Bt cells. Our findings confirmed that plant polysaccharides modulate biofilm formation and insecticidal activities of Bt strains and built a foundation for the construction of biofilm-type Bt biopesticides.

Emerging Applications of Bacteriocins as Antimicrobials, Anticancer Drugs, and Modulators of The Gastrointestinal Microbiota

The use of bacteriocins holds great promise in different areas such as health, food, nutrition, veterinary, nanotechnology, among others. Many research groups worldwide continue to advance the knowledge to unravel a novel range of therapeutic agents and food preservatives. This review addresses the advances of bacteriocins and their producer organisms as biocontrol agents for applications in the medical industry and agriculture. Furthermore, the bacteriocin mechanism of action and structural characteristics will be reviewed. Finally, the potential role of bacteriocins to modulate the signaling in host-associated microbial communities will be discussed.

Bacillus sp. Bacteriocins: Natural Weapons against Bacterial Enemies

BACKGROUND

Currently, antibiotic-resistant pathogenic bacteria are emerging as an important health problem worldwide. The search for new compounds with antibiotic characteristics is the most promising alternative. Bacteriocins are natural compounds that are inhibitory against pathogens, and Bacillus species are the major producers of these compounds, which have shown antimicrobial activity against clinically important bacteria. These peptides not only have potential in the pharmaceutical industry but also in food and agricultural sectors.

OBJECTIVE

We provide an overview of the recent bacteriocins isolated from different species of Bacillus including their applications and the older bacteriocins.

RESULTS

In this review, we have revised some works about the improvements carried out in the production of bacteriocins.

CONCLUSION

These applications make bacteriocins very promising compounds that need to study for industrial production.

Biomanufacturing process for the production of bacteriocins from Bacillaceae family

Members of Bacillaceae family are of major interest in medical industry due to vast antimicrobial peptides they produce as therapeutic agents. For decades, synthetic and natural occurring antibiotics have been used to treat infectious diseases, but heavy dependence on these drugs has led to significant drawbacks which propel continuous development of new antibiotics generation. Recent findings have shown several bacteriocins of Bacillaceae as promising alternatives to the conventional drugs to combat the emergence of new drug-resistant pathogens. In this present review, Bacillaceae bacteriocins’ classification such as lantibiotics and thiazole/oxazole-modified microcins as well as their biochemical characterization such as sensitivity to enzymes, temperature, pH and chemicals are described. This article enlightens on the medical application of several Bacillaceae bacteriocins emphasizing those that underwent and on-going preclinical trials. This review also discusses the development of Bacillaceae bacteriocins production, focusing strains selection and fermentation factors such as inocula size, medium (carbon, nitrogen, minerals sources), temperature, pH, agitation and aeration rate, dissolved oxygen tension (DOT), fermentation time, inducers and mode of operation via various statistical methods for their optimization. It also highlights recent advance in the production of bioengineered and recombinant bacteriocins in bioreactors system which are rarely disclosed in literature.

Mesenchymal stem cell-gut microbiota interaction in the repair of inflammatory bowel disease: an enhanced therapeutic effect

BACKGROUND

Several investigations affirm that, patients with inflammatory bowel disease (IBD) exhibit dysbiosis characterized by restricted biodiversity and imbalanced bacterial composition intertwined with immune dysregulation. The interaction between stem cells and gut microbiota is a novel and highly promising field that could add up to a better understanding of the gut physiology, as well as therapeutic improvement towards diseases like IBD. Through direct contact or release of products and/or metabolites, gut bacteria regulate gut homeostasis, damage repair, regeneration and differentiation of stem cells. In the same way, mesenchymal stem cells (MSCs) produce similar effects including restoration of gut-microbiome composition. BODY: We reviewed the anti-inflammatory, antimicrobial, pathogenic bacterial clearance, proliferation and tissue remodeling effects of mesenchymal stem cells (MSCs) and fecal microbiota transplantation (FMT) as separate transplants in IBD, and the outcome of the interaction between MSCs and gut microbiota.

CONCLUSION

The two therapies share several points of connection in therapeutics with enhanced functionalities in their interaction with each other. Focused investigations of MSC-gut bacteria interactions could lead to a novel discovery in therapeutics. We also anticipate an improved clinical remission rate in a combined FMT-MSC transplantation approach in IBD than the current single FMT or MSC approach.

Identification and partial purification of thuricin 4AJ1 produced by Bacillus thuringiensis

Thuricin 4AJ1, produced by Bacillus thuringiensis strain 4AJ1, showed inhibition activity against Bacillus cereus 0938 and ATCC 10987. It began to appear in the stationary phase and reached its maximum activity level of 209.958 U at 18 h against B. cereus 0938 and 285.689 U at 24 h against B. cereus ATCC 10987. Tricine-SDS-PAGE results showed that the partly purified thuricin 4AJ1 was about 6.5 kDa. The molecular weights of the known B. thuringiensis bacteriocins and the ones obtained by the two mainstream websites for predicting bacteriocins were inconsistent with the size of the thuricin 4AJ1, indicating that the bacteriocin obtained in this study may have a novel structure. Based on the biochemical properties, the thuricin 4AJ1 activities increased after treatment with proteinase K and lipase II, and were not affected by a-amylase, catalase, α-chymotrypsin VII and α-chymotrypsin II. It was heat tolerant, being active up to 90º C. In the pH 3-10 range, it maintained most of its activity. Finally, the sensitivity of the strain 4AJ1 to commonly used antibiotics was tested. In view of its stability and antibacterial activity, thuricin 4AJ1 may be applied as a food biopreservative.

Structure and mode of action of a novel antibacterial peptide from the blood of Andrias davidianus

Andrias davidianus is widely recognized in traditional medicine as a cure-all to treat a plethora of ailments. In a previous study, a novel antibacterial peptide named andricin B was isolated from A. davidianus blood. In this study, we investigated andricin B structure and its mode of action. Circular dichroism spectra suggested that andricin B adopts a random coil state in aqueous solution and a more rigid conformation in the presence of bacteria. Moreover propidium iodide/fluorescein diacetate double staining indicated that bacteria treated with andricin B were not immediately eliminated. Rather, there is a gradual bacterial death, followed by a sublethal stage. Scanning electronic microscope imaging indicates that andricin B might form pores on cell membranes, leading to the release of cytoplasmic contents. These results were consistent with flow cytometry analysis. Furthermore, Fourier transform infrared spectroscopy suggests that andricin B induces changes in the chemical properties in the areas surrounding these "pores" on the cell membranes. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this study suggested the new perspectives about the mode of action of antimicrobial peptide (AMP) active against sensitive bacteria. The AMP was able to be in a random coiled state in aqueous solution but to change to a more rigid one in the presence of sensitive bacteria. Exposure to AMP might not lead to immediate death of treated bacteria, rather bacteria concentration decreased gradually flattening at a sublethal stage. These findings will help people to understand better how the AMPs activate against sensitive bacteria.

Heterologous expression and purification of BtCspB, a novel cold-shock protein-like bacteriocin from Bacillus thuringiensis BRC-ZYR2

A novel Bacillus thuringiensis (Bt) bacteriocin BtCspB, active against a food-borne pathogen Bacillus cereus, was identified and purified by a traditional four-step chromatographic process with low yield (44.5 µg/L) in our lab previously. The aim of this study was to dramatically increase its yield by heterologous expression of BtCspB. The BtCspB gene from Bt BRC-ZYR2 was successfully heterologously expressed in Escherichia coli BL21 (DE3). Affinity chromatography was used to obtain the pure BtCspB up to 20 mg/L. The purified BtCspB showed a MIC value of 12.5 µg/mL and a MBC value of 50.0 µg/mL against Bacillus cereus ATCC 10987. The bacteriocin activity of BtCspB against B. cereus ATCC 10987 was further directly detected in a gel-overlay assay. The anti-B. cereus activity, however, was lower than the bacteriocin purified by the traditional four-step chromatographic process probably because of structural modifications. Compared with the traditional method, the yield of the bacteriocin by heterologous expression increased by 449 times, and the purification step was dramatically simplified, which laying a foundation for the industrial production of this novel cold-shock protein-like bacteriocin BtCspB active against B. cereus.

Antibacterial Activity, Cytotoxicity, and the Mechanism of Action of Bacteriocin from Bacillus subtilis GAS101

OBJECTIVE

The aim of this study was to purify and characterize bacteriocin from the soil isolate Bacillus subtilis GAS101, and to determine its antimicrobial as well as antibiofilm potential. The purified bacteriocin was further analyzed and evaluated for mammalian cell cytotoxicity and the possible mode of action.

MATERIAL AND METHODS

Bacteriocin from B. subtilis GAS101 (an animal husbandry soil isolate) was partially purified and checked for antimicrobial and antibiofilm activity against gram-positive and gram-negative bacteria. The molecular weight of bacteriocin was determined using tricine SDS-PAGE gel. The stability of bacteriocin was investigated at various temperatures and pH levels, and its sensitivity towards 8 enzymes and 6 chemicals was determined. Cytotoxicity analysis was performed on a Vero cell line by a tetrazolium dye-based assay. Scanning electron microscopy (SEM) of bacteriocin-treated bacteria was carried out to determine the possible mode of action.

RESULTS

Bacteriocin from B. subtilis GAS101 was a potential inhibitor of both the indicator organisms (Staphylococcus epidermidis and Escherichia coli), and had a molecular weight of approximately 6.5 kDa. An in situ gel assay showed a zone of inhibition corresponding to the estimated protein band size. Bacteriocin was stable and showed antibacterial activity in broad ranges of temperature (30-121°C) and pH (2-12). It was sensitive to 4 proteolytic enzymes, which indicated its proteinaceous nature. Bacteriocin showed > 70% cell viability on the mammalian Vero cell line. SEM depicted that the bacteriocin was able to disrupt the bacterial cell membrane as its probable mode of action.

CONCLUSION

Thermostable and pH-tolerant bacteriocin from B. subtilis GAS101, of about 6.5 kDa, showed broad-spectrum antimicrobial and antibiofilm activity.

Gut microbiota in the pathogenesis of inflammatory bowel disease

Inflammatory bowel disease (IBD), including ulcerative colitis and Crohn's disease, is a chronic and relapsing inflammatory disorder of the intestine. Although its incidence is increasing globally, the precise etiology remains unclear and a cure for IBD has yet to be discovered. The most accepted hypothesis of IBD pathogenesis is that complex interactions between genetics, environmental factors, and the host immune system lead to aberrant immune responses and chronic intestinal inflammation. The human gut harbors a complex and abundant aggregation of microbes, collectively referred to as the gut microbiota. The gut microbiota has physiological functions associated with nutrition, the immune system, and defense of the host. Recent advances in next-generation sequencing technology have identified alteration of the composition and function of the gut microbiota, which is referred to as dysbiosis, in IBD. Clinical and experimental data suggest dysbiosis may play a pivotal role in the pathogenesis of IBD. This review is focused on the physiological function of the gut microbiota and the association between the gut microbiota and pathogenesis in IBD. In addition, we review the therapeutic options for manipulating the altered gut microbiota, such as probiotics and fecal microbiota transplantation.

The adsorption features between insecticidal crystal protein and nano-Mg(OH)2

Nano-Mg(OH)₂, with low biological toxicity, is an ideal nano-carrier for insecticidal protein to improve the bioactivity. In this work, the adsorption features of insecticidal protein by nano-Mg(OH)₂ have been studied. The adsorption capacity could reach as high as 136 mg g^-1, and the adsorption isotherm had been fitted with Langmuir and Freundlich models. Moreover, the adsorption kinetics followed a pseudo-first or -second order rate model, and the adsorption was spontaneous and an exothermic process. However, high temperatures are not suitable for adsorption, which implies that the temperature would be a critical factor during the adsorption process. In addition, FT-IR confirmed that the protein was adsorbed on the nano-Mg(OH)₂, zeta potential analysis suggested that insecticidal protein was loaded onto the nano-Mg(OH)₂ not by electrostatic adsorption but maybe by intermolecular forces, and circular dichroism spectroscopy of Cry11Aa protein before and after loading with nano-Mg(OH)₂ was changed. The study applied the adsorption information between Cry11Aa and nano-Mg(OH)₂, which would be useful in the practical application of nano-Mg(OH)₂ as a nano-carrier.