Natural products from Bacillus subtilis with antimicrobial properties

Combinative effect of pulsed-light irradiation and solid-state fermentation on ginkgolic acids, ginkgols, ginkgolides, bilobalide, flavonoids, product quality and sensory assessment of Ginkgo biloba dark tea

Pulsed light (PL) is a prospective non-thermal technology that can improve the degradation of ginkgolic acid (GA) and retain the main bioactive compounds in Ginkgo biloba leaves (GBL). However, only using PL hasn't yet achieved the ideal effect of reducing GA. Fermentation of GBL to make ginkgo dark tea (GDT) could decrease GA. Because different microbial strains are used for fermentation, their metabolites and product quality might differ. However, there is no research on the combinative effect of PL irradiation fixation and microbial strain fermentation on main bioactive compounds and sensory assessment of GDT. In this research, first, Bacillus subtilis and Saccharomyces cerevisiae were selected as fermentation strains that can reduce GA from the five microbial strains. Next, the fresh GBL was irradiated by PL for 200 s (fluences of 0.52 J/cm2), followed by B. subtilis, S. cerevisiae, or natural fermentation to make GDT. The results showed that compared with the control (unirradiated and unfermented GBL) and the only PL irradiated GBL, the GA in GDT using PL + B. subtilis fermentation was the lowest, decreasing by 29.74%; PL + natural fermentation reduced by 24.53%. The total flavonoid content increased by 14.64% in GDT using PL + B. subtilis fermentation, whose phenolic and antioxidant levels also increased significantly. Sensory evaluation showed that the color, aroma, and taste of the tea infusion of PL + B. subtilis fermentation had the highest scores. In conclusion, the combined PL irradiation and solid-state fermentation using B. subtilis can effectively reduce GA and increase the main bioactive compounds, thus providing a new technological approach for GDT with lower GA.

Bioactive compounds from food-grade Bacillus

Bacillus species have attracted significant attention in recent years due to their potential for producing various bioactive compounds with diverse functional properties. This review highlights bioactive substances from food-grade Bacillus strains and their applications in functional foods and nutraceuticals. The metabolic capacities of Bacillus species have allowed them to generate a wide range of bioactive substances, including vitamins, enzymes, anti-microbial peptides, and other non-ribosomal peptides. These substances have a variety of positive effects, including potential cholesterol-lowering and immune-modulatory qualities in addition to anti-oxidant and anti-bacterial actions. The uses and mechanisms of action of these bioactive chemicals can be used to improve the functional qualities and nutritional profile of food products. Examples include the use of anti-microbial peptides to increase safety and shelf life, as well as the use of Bacillus-derived enzymes in food processing to improve digestibility and sensory qualities. The exploitation of bioactive compounds from food-grade Bacillus strains presents a promising frontier in the development of functional foods and nutraceuticals with enhanced health benefits. Due to their wide range of activity and applications, they are considered as important resources for the development of novel medications, agricultural biocontrol agents, and industrial enzymes. Ongoing research into the biosynthetic pathways, functional properties, and applications of these compounds is essential to fully realize their potential in the food industry. This review underscores the significance of various bioactive compounds generated from Bacillus in tackling global issues like environmental sustainability, sustainable agriculture, and antibiotic resistance. Future developments in microbiology and biotechnology will enable us to fully utilize the potential of these amazing microbes, resulting in novel approaches to industry, agriculture, and health. © 2024 Society of Chemical Industry.

The evaluation of next-generation probiotics on broiler growth performance, gut morphology, gut microbiome, nutrient digestibility, in addition to enzyme production of Bacillus spp. in vitro

Considerable research has been conducted into the efficacy of individual probiotics in broiler production, however information on the most effective combinations of synergistic Bacillus probiotic is lacking. This study investigated the impact of different Bacillus strain combinations in broiler chickens, as well as in vitro enzyme production. In experiment one, a total of 576 Ross 308 broilers at 1 d old were grown for 21 d across 6 treatments of maize-soybean diets (n = 12 pens per treatment) to compare three different strain combinations (formulation 1 [F1]: 3 strains Bacillus amyloliquefaciens; F2: Bacillus coagulans and 2 strains B. amyloliquefaciens; F3: B. coagulans, Bacillus licheniformis and 2 strains B. amyloliquefaciens; F5: Bacillus subtilis, B. licheniformis and 2 strains B. amyloliquefaciens), positive control (PC), and a negative control antibiotic treatment group (NC). In Exp. 2, a total of 360 one-day-old ROSS308 broilers were used to test five treatments (n = 9) including PC, NC, F1 and F5 (selected from Exp. 1), and F4 (Bacillus pumilis and 2 strains B. amyloliquefaciens) in a maize-soybean diet. B. amyloliquefaciens F1 demonstrated a significant improvement in feed conversion ratio (FCR) compared to F2 at d 14 (1.49 vs 2.10; P = 0.038) and the body weight (BW) at d 21 (847.0 g vs 787.4 g) compared to other combinations (P = 0.027). The FCR at d 21 tended to be lower in birds fed F1 (1.46 vs 1.66) compared to the control (P = 0.068). Probiotic treatments had significantly improved nutrient digestibility compared to the PC and NC. Also, probiotic treatments supported the growth of Streptococcus, a common commensal genus and reduced the abundance of genera that correlated with low weight gain such as Akkermansia. Experiment two revealed that F4 improved FCR (P < 0.001) and BW at 28 d (P = 0.014). In vitro testing showed a high production of protease and amylase by Bacillus. Thus, the addition of Bacillus probiotics, particularly containing B. amyloliquefaciens strains and Bacillus pumilus, into the diet of broiler chickens improves production performance, nutrient digestibility, and allows the proliferation of beneficial gut microbiota.

Agro Active Potential of Bacillus subtilis PE7 against Didymella bryoniae (Auersw.), the Causal Agent of Gummy Stem Blight of Cucumis melo

Microbial agents such as the Bacillus species are recognized for their role as biocontrol agents against various phytopathogens through the production of diverse bioactive compounds. This study evaluates the effectiveness of Bacillus subtilis PE7 in inhibiting the growth of Didymella bryoniae, the pathogen responsible for gummy stem blight (GSB) in cucurbits. Dual culture assays demonstrate significant antifungal activity of strain PE7 against D. bryoniae. Volatile organic compounds (VOCs) produced by strain PE7 effectively impede mycelial formation in D. bryoniae, resulting in a high inhibition rate. Light microscopy revealed that D. bryoniae hyphae exposed to VOCs exhibited abnormal morphology, including swelling and excessive branching. Supplementing a potato dextrose agar (PDA) medium with a 30% B. subtilis PE7 culture filtrate significantly decreased mycelial growth. Moreover, combining a 30% culture filtrate with half the recommended concentration of a chemical fungicide yielded a more potent antifungal effect than using the full fungicide concentration alone, inducing dense mycelial formation and irregular hyphal morphology in D. bryoniae. Strain PE7 was highly resilient and was able to survive in fungicide solutions. Additionally, B. subtilis PE7 enhanced the nutrient content, growth, and development of melon plants while mitigating the severity of GSB compared to fungicide and fertilizer treatments. These findings highlight B. subtilis PE7 as a promising biocontrol candidate for integrated disease management in crop production.

Characterization and genome mining of Bacillus subtilis BDSA1 isolated from river water in Bangladesh: A promising bacterium with diverse biotechnological applications

The metabolic versatility of Bacillus subtilis makes it useful for a wide range of applications in biotechnology, from bioremediation to industrially important metabolite production. Understanding the molecular attributes of the biocontrol characteristics of B. subtilis is necessary for its tailored use in the environment and industry. Therefore, the present study aimed to conduct phenotypic characterization and whole genome analysis of the B. subtilis BDSA1 isolated from polluted river water from Dhaka, Bangladesh to explore its biotechnological potential. The chromium reduction capacity at 100 ppm Cr (VI) showed that B. subtilis BDSA1 reduced 40 % of Cr (VI) within 24hrs at 37 °C. Exposure of this bacterium to 200 ppm cadmium resulted in 43 % adsorption following one week of incubation at 37 °C. Molecular detection of chrA and czcC gene confirmed chromium and cadmium resistance characteristics of BDSA1. The size of the genome of the B. subtilis BDSA1 was 4.2 Mb with 43.4 % GC content. Genome annotation detected the presence of numerous genes involved in the degradation of xenobiotics, resistance to abiotic stress, production of lytic enzymes, siderophore formation, and plant growth promotion. The assembled genome also carried chromium, cadmium, copper, and arsenic resistance-related genes, notably cadA, czcD, czrA, arsB etc. Genome mining revealed six biosynthetic gene clusters for bacillaene, bacillibacin, bacilysin, subtilosin, fengycin and surfactin. Importantly, BDSA1 was predicted to be non-pathogenic to humans and had only two acquired antimicrobial resistance genes. The pan-genome analysis showed the openness of the B. subtilis pan-genome. Our findings suggested that B. subtilis BDSA1 might be a promising candidate for diverse biotechnological uses.

Total synthesis of antifungal lipopeptide iturin A analogues and evaluation of their bioactivity against F. graminearum

The pursuit of novel antifungal agents is imperative to tackle the threat of antifungal resistance, which poses major risks to both human health and to food security. Iturin A is a cyclic lipopeptide, produced by Bacillus sp., with pronounced antifungal properties against several pathogens. Its challenging synthesis, mainly due to the laborious synthesis of the β-amino fatty acid present in its structure, has hindered the study of its mode of action and the development of more potent analogues. In this work, a facile synthesis of bioactive iturin A analogues containing an alkylated cysteine residue is presented. Two analogues with opposite configurations of the alkylated cysteine residue were synthesized, to evaluate the role of the stereochemistry of the newly introduced amino acid on the bioactivity. Antifungal assays, conducted against F. graminearum, showed that the novel analogues are bioactive and can be used as a synthetic model for the design of new analogues and in structure-activity relationship studies. The assays also highlight the importance of the β-amino acid in the natural structure and the role of the stereochemistry of the amino fatty acid, as the analogue with the D configuration showed stronger antifungal properties than the one with the L configuration.

Bacterial Lipopeptides Are Effective against Pear Fire Blight

Fire blight, a devastating disease caused by Erwinia amylovora, poses a significant threat to pear and apple trees in Xinjiang province, China. In an effort to combat this pathogen, we isolated 10 bacteria from various components of apple and crabapple trees and conducted screenings to assess their ability to inhibit E. amylovora in vitro. Through biochemical tests and partial 16S rRNA gene sequencing, we identified two promising strains, Priestia megaterium strain H1 and Bacillus subtilis strain I2. These strains were then evaluated for their efficacy in biocontrol under controlled laboratory conditions, focusing on immature fruits and leaves. Remarkably, all selected antagonists exhibited the capability to reduce the severity of the disease on both fruit and leaves. P. megaterium strain H1 and B. subtilis strain I2 exhibited significant reductions in disease incidence on both immature fruits and leaves compared to the control. Specifically, on immature fruits, they achieved reductions of 53.39% and 44.76%, respectively, while on leaves, they demonstrated reductions of 59.55% and 55.53%, respectively. Furthermore, during the study, we detected the presence of lipopeptides, including surfactin, iturins, bacillomycin D, and fengycins, in the methanol extract obtained from these two antagonistic bacteria using thin-layer chromatography (TLC). Based on the results obtained, B. subtilis strain I2 and P. megaterium strain H1 exhibit considerable potential for controlling fire blight. However, further evaluation of their efficacy under natural field conditions is essential to validate their practicality as a biocontrol method.

Biocontrol mechanisms of Bacillus: Improving the efficiency of green agriculture

Species of the genus Bacillus have been widely used for the biocontrol of plant diseases in the demand for sustainable agricultural development. New mechanisms underlying Bacillus biocontrol activity have been revealed with the development of microbiome and microbe-plant interaction research. In this review, we first briefly introduce the typical Bacillus biocontrol mechanisms, such as the production of antimicrobial compounds, competition for niches/nutrients, and induction of systemic resistance. Then, we discussed in detail the new mechanisms of pathogen quorum sensing interference and reshaping of the soil microbiota. The "cry for help" mechanism was also introduced, in which plants can release specific signals under pathogen attack to recruit biocontrol Bacillus for root colonization against invasion. Finally, two emerging strategies for enhancing the biocontrol efficacy of Bacillus agents, including the construction of synthetic microbial consortia and the application of rhizosphere-derived prebiotics, were proposed.

Bacillus subtilis RBT-7/32 and Bacillus licheniformis RBT-11/17 as New Promising Strains for Use in Probiotic Feed Additives

The normal functioning of a gastrointestinal microflora in poultry and livestock is of significant importance, since its imbalance negatively influences an organism's functions. In this study, the UV mutagenesis and selection were used to obtain two Bacillus strains possessing antagonistic activity towards Escherichia coli and Staphylococcus aureus, and their potential as a probiotic feed additive was evaluated. Compared to the parental strains, the ability of B. subtilis RBT-7/32 and B. licheniformis RBT-11/17 strains to suppress E. coli increased by 77 and 63%, respectively; the corresponding ability of these strains to suppress S. aureus increased by 80 and 79%, respectively. RBT-11/17 could not utilize microcrystalline cellulose and carboxymethyl cellulose, whereas cellulolytic activity of RBT-7/32 was doubled compared to the initial strain. The amylolytic activity of new strains was increased by 40%. Cultivation of strains on media containing soybean, pea, and corn meal did not provide any difference in the biomass production compared to the control. The heating of a water suspension of a dried biomass of the strains for 10-20 min at 80 and 100 °C or incubation in water solutions of citric, ascorbic, acetic, and formic acids (pH 3.0) for 3 and 24 h at 40 °C did not provide any negative influence on the spore survivability. Both strains were evaluated for their resistance to a number of veterinary antibiotics. Thus, RBT-7/32 and RBT-11/17 strains have good prospects for use in feed additives.

Modeling and optimization of antibacterial effect of lichen-associated bacteria, Bacillus subtilis KSRLAB3 strain against marine fouling bacteria, Vibrio alginolyticus

One of the most commonly occurring bacteria, Bacillus subtilis, can produce a wide variety of secondary metabolites. In this study, the antimicrobial effect of B. subtilis KSRLAB3 against Vibrio alginolyticus was optimized using the Plackett-Burman design (PBD) method, response surface methodology (RSM), and genetic algorithm (GA). Initially, the effects of carbon source, nitrogen source, NaCl concentration, pH, temperature, and incubation time on antimicrobial effects were studied. Among the carbon and nitrogen sources investigated, mannose and peptone elicited maximum antimicrobial effect. Using PBD, the most significant variables that influence the antimicrobial effect were identified, including incubation time, peptone concentration, and temperature. The optimum conditions required for attaining maximum antimicrobial effect was identified using the RSM-GA hybrid method, and the optimum condition includes 49.999 h of incubation time, 4.39 g/L of peptone concentration, and 27.629°C of incubation temperature. The confirmatory experiments performed around the optimum condition showed a zone of inhibition of 35 ± 0.52 mm. Methanolic extract also proved the presence of antibacterial lipopeptide surfactin. Therefore, the RSM-GA hybrid method was successfully used in this study to model the antimicrobial effect of B. subtilis KSRLAB3 against V. alginolyticus. The effective inhibition of V. alginolyticus can be investigated further for the development of antifouling coatings.

Protective Effects of Bacillus subtilis HH2 against Oral Enterotoxigenic Escherichia coli in Beagles

This study evaluated the protective effect of Bacillus subtilis HH2 on beagles orally challenged with enterotoxigenic Escherichia coli (ETEC). We assessed the physiological parameters and the severity of diarrhea, as well as the changes in three serum immunoglobulins (IgG, IgA, and IgM), plasma diamine oxidase (DAO), D-lactate (D-LA), and the fecal microbiome. Feeding B. subtilis HH2 significantly reduced the severity of diarrhea after the ETEC challenge (p < 0.05) and increased serum levels of IgG, IgA, and IgM (p < 0.01). B. subtilis HH2 administration also reduced serum levels of DAO at 48 h after the ETEC challenge (p < 0.05), but no significant changes were observed in D-LA (p > 0.05). Oral ETEC challenge significantly reduced the richness and diversity of gut microbiota in beagles not pre-fed with B. subtilis HH2 (p < 0.05), while B. subtilis HH2 feeding and oral ETEC challenge significantly altered the gut microbiota structure of beagles (p < 0.01). Moreover, 14 days of B. subtilis HH2 feeding reduced the relative abundance of Deinococcus-Thermus in feces. This study reveals that B. subtilis HH2 alleviates diarrhea caused by ETEC, enhances non-specific immunity, reduces ETEC-induced damage to the intestinal mucosa, and regulates gut microbiota composition.

Classification and Multifaceted Potential of Secondary Metabolites Produced by Bacillus subtilis Group: A Comprehensive Review

Despite their remarkable biosynthetic potential, Bacillus subtilis have been widely overlooked. However, their capability to withstand harsh conditions (extreme temperature, Ultraviolet (UV) and γ-radiation, and dehydration) and the promiscuous metabolites they synthesize have created increased commercial interest in them as a therapeutic agent, a food preservative, and a plant-pathogen control agent. Nevertheless, the commercial-scale availability of these metabolites is constrained due to challenges in their accessibility via synthesis and low fermentation yields. In the context of this rising in interest, we comprehensively visualized the antimicrobial peptides produced by B. subtilis and highlighted their prospective applications in various industries. Moreover, we proposed and classified these metabolites produced by the B. subtilis group based on their biosynthetic pathways and chemical structures. The biosynthetic pathway, bioactivity, and chemical structure are discussed in detail for each class. We believe that this review will spark a renewed interest in the often disregarded B. subtilis and its remarkable biosynthetic capabilities.

Determination of Taxonomic Affiliation and Assessment of Biotechnological Potential of an Indigenous Strain of Gram-Positive Spore-Forming Bacteria

The search for new effective strains-producers of enzymes and biologically active substances for the development of new environmentally friendly plant protection products against phytopathogens is a very urgent task for the greening of agriculture. In our work, we used active strains of gram-positive spore-forming bacteria isolated from soil near the roadside zone of the Belgorod region to assess their antagonistic activity to phytopathogens and biotechnological potential. In the course of molecular genetic studies of the 16S rRNA gene of the isolated native strain, a complete similarity of the target with Bacillus subtilis was revealed. When studying morphological and cultural characteristics, it was determined that the cells of the target strain are rod-shaped, arranged singly or in pairs.The conditions of cultivation of the bacterium were revealed, which shows high growth in the composition of the medium containing 3% peptone for 20 hours, the specific increase in biomass exceeded 96%. When evaluating the antagonistic activity, it was revealed that the isolated strain suppresses the growth of cultures of Escherichia coli O157:H7, Aspergillus unguis VKM F-1754 and bacteria of the genus Ralstonia.

Cell-Free Supernatants (CFSs) from the Culture of Bacillus subtilis Inhibit Pseudomonas sp. Biofilm Formation

Biofilm inhibition has been identified as a novel drug target for the development of broad-spectrum antibiotics to combat infections caused by drug-resistant bacteria. Although several plant-based compounds have been reported to have anti-biofilm properties, research on the anti-biofilm properties of bacterial bioactive compounds has been sparse. In this study, the efficacy of compounds from a cell-free supernatant of Bacillus subtilis against a biofilm formation of Pseudomonas sp. was studied through in vitro, in vivo and in silico studies. Here, in well diffusion method, Bacillus subtilis demonstrated antibacterial activity, and more than 50% biofilm inhibition activity against Pseudomonas sp. was exhibited through in vitro studies. Moreover, molecular docking and molecular dynamics (MD) simulation gave insights into the possible mode of action of the bacterial volatile compounds identified through GC-MS to inhibit the biofilm-formation protein (PDB ID: 7M1M) of Pseudomonas sp. The binding energy revealed from docking studies ranged from -2.3 to -7.0 kcal mol-1. Moreover, 1-(9H-Fluoren-2-yl)-2-(1-phenyl-1H-ttetrazole5-ylsulfanyl)-ethanone was found to be the best-docked compound through ADMET and pharmacokinetic properties. Furthermore, MD simulations further supported the in vitro studies and formed a stable complex with the tested protein. Thus, this study gives an insight into the development of new antibiotics to combat multi-drug-resistant bacteria.

Efficacy of Bacillus subtilis (Ehrenberg1835) Cohn1872, in suppressing Fusarium oxysporum Schlecht. emend. Snyder & Hansen, the causal agent of root rot of date palm offshoots (Phoenix dactylifera L.) in Iraq

Date palm root rot disease is one of the most important diseases of date palms and offshoots. It is caused by many soil-borne pathogenic fungi. Pathogenicity assays of the isolated fungi showed that the major causative agents of root rot disease in date palm plantlets were Fusarium oxysporum Schlecht. emend. Snyder & Hansen, F. proliferatum (Matsush.) Nirenberg ex Gerlach & Nirenberg S1, F. proliferatum S2, Gibberella fujikuroi (Sawada) Wollenw., and Rhizoctonia solani J.G. Kühn. The most virulent fungus was F. oxysporum with a severity index of 82.16 % of root rot, while R. solani was the least harmful with a disease severity rate of 12.42 %. In laboratory tests, Bacillus subtilis reduced the radial mycelial growth of F. oxysporum on PDA medium by 86.6 %. The application of B. subtilis in combination with F. oxysporum substantially inhibited the severity of root rot disease relative to plantlets treated with only F. oxysporum. In addition, B. subtilis application in the presence or absence of F. oxysporum improved the plant physiology of plantlets, including total chlorophyll, total carotenoid, antioxidant enzyme levels (catalase and peroxidase), and total proline content.

Bacillus for Plant Growth Promotion and Stress Resilience: What Have We Learned?

The rhizosphere is a thin film of soil that surrounds plant roots and the primary location of nutrient uptake, and is where important physiological, chemical, and biological activities are occurring. Many microbes invade the rhizosphere and have the capacity to promote plant growth and health. Bacillus spp. is the most prominent plant growth promoting rhizobacteria due to its ability to form long-lived, stress-tolerant spores. Bacillus-plant interactions are driven by chemical languages constructed by a wide spectrum of metabolites and lead to enhanced plant growth and defenses. Thus, this review is a synthesis and a critical assessment of the current literature on the application of Bacillus spp. in agriculture, highlighting gaps that remain to be explored to improve and expand on the Bacillus-based biostimulants. Furthermore, we suggest that omics sciences, with a focus on metabolomics, offer unique opportunities to illuminate the chemical intercommunications between Bacillus and plants, to elucidate biochemical and molecular details on modes of action of Bacillus-based formulations, to generate more actionable insights on cellular and molecular events that explain the Bacillus-induced growth promotion and stress resilience in plants.

Rhizospheric microorganisms: The gateway to a sustainable plant health

Plant health is essential for food security, and constitutes a major predictor to safe and sustainable food systems. Over 40% of the global crops' productions are lost to pests, insects, diseases, and weeds, while the routinely used chemical-based pesticides to manage the menace also have detrimental effects on the microbial communities and ecosystem functioning. The rhizosphere serves as the microbial seed bank where microorganisms transform organic and inorganic substances in the rhizosphere into accessible plant nutrients as plants harbor diverse microorganisms such as fungi, bacteria, nematodes, viruses, and protists among others. Although, the pathogenic microbes initiate diseases by infiltrating the protective microbial barrier and plants' natural defense systems in the rhizosphere. Whereas, the process is often circumvented by the beneficial microorganisms which antagonize the pathogens to instill disease resistance. The management of plant health through approaches focused on disease prevention is instrumental to attaining sustainable food security, and safety. Therefore, an in-depth understanding of the evolving and succession of root microbiomes in response to crop development as discussed in this review opens up new-fangled possibilities for reaping the profit of beneficial root–microbiomes' interactions toward attaining sustainable plant health.

Biocontrol of Wheat Crown Rot Using Bacillus halotolerans QTH8

Fusarium pseudograminearum causes crown rot in wheat. This study aimed to assess the effects of the bacterial strain QTH8 isolated from Cotinus coggygria rhizosphere soil against F. pseudograminearum. Bacterial strain QTH8 was identified as Bacillus halotolerans in accordance with the phenotypic traits and the phylogenetic analysis of 16S rDNA and gyrB gene sequence. Culture filtrates of bacterial strain QTH8 inhibited the mycelial growth of F. pseudograminearum and resulted in mycelial malformation such as tumor formation, protoplast condensation, and mycelial fracture. In addition, bacterial strain QTH8 also inhibited the mycelial growth of Hainesia lythri, Pestalotiopsis sp., Botrytis cinerea, Curvularia lunata, Phyllosticta theaefolia, Fusarium graminearum, Phytophthora nicotianae, and Sclerotinia sclerotiorum. The active compounds produced by bacterial strain QTH8 were resistant to pH, ultraviolet irradiation, and low temperature, and were relatively sensitive to high temperature. After 4 h exposure, culture filtrates of bacterial strain QTH8—when applied at 5%, 10%, 15%, 20%, 25%, and 30%—significantly reduced conidial germination of F. pseudograminearum. The coleoptile infection assay proved that bacterial strain QTH8 reduced the disease index of wheat crown rot. In vivo application of QTH8 to wheat seedlings decreased the disease index of wheat crown rot and increased root length, plant height, and fresh weight. Iturin, surfactin, and fengycin were detected in the culture extract of bacterial strain QTH8 by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Bacterial strain QTH8 was identified for the presence of the ituC, bacA, bmyB, spaS, srfAB, fend, and srfAA genes using the specific polymerase chain reaction primers. B. halotolerans QTH8 has a vital potential for the sustainable biocontrol of wheat crown rot.

Quantitative High-Throughput Screening Methods Designed for Identification of Bacterial Biocontrol Strains with Antifungal Properties

Large screens of bacterial strain collections to identify potential biocontrol agents often are time-consuming and costly and fail to provide quantitative results. In this study, we present two quantitative and high-throughput methods to assess the inhibitory capacity of bacterial biocontrol candidates against fungal phytopathogens. One method measures the inhibitory effect of bacterial culture supernatant components on the fungal growth, while the other accounts for direct interaction between growing bacteria and the fungus by cocultivating the two organisms. The antagonistic supernatant method quantifies the culture components' antifungal activity by calculating the cumulative impact of supernatant addition relative to the growth of a nontreated fungal control, while the antagonistic cocultivation method identifies the minimal bacterial cell concentration required to inhibit fungal growth by coinoculating fungal spores with bacterial culture dilution series. Thereby, both methods provide quantitative measures of biocontrol efficiency and allow prominent fungal inhibitors to be distinguished from less effective strains. The combination of the two methods sheds light on the types of inhibition mechanisms and provides the basis for further mode-of-action studies. We demonstrate the efficacy of the methods using Bacillus spp. with different levels of antifungal activities as model antagonists and quantify their inhibitory potencies against classic plant pathogens. IMPORTANCE Fungal phytopathogens are responsible for tremendous agricultural losses on an annual basis. While microbial biocontrol agents represent a promising solution to the problem, there is a growing need for high-throughput methods to evaluate and quantify inhibitory properties of new potential biocontrol agents for agricultural application. In this study, we present two high-throughput and quantitative fungal inhibition methods that are suitable for commercial biocontrol screening.

Bacillus symbiont drives alterations in intestinal microbiota and circulating metabolites of lepidopteran host

The symbiotic association between bacterial symbionts and insect hosts is a complicated process that is not completely understood. Herein, we used a silkworm model to study the association between symbiotic Bacillus and lepidopteran insect by investigating the changes in intestinal microbiota and hemolymph circulating metabolites of silkworm after symbiotic Bacillus subtilis treatment. Results showed that B. subtilis can generate a variety of primary and secondary metabolites, such as B vitamins and antimicrobial compounds, to provide micronutrients and enhance the pathogen resistance of their insect host. Shifts in the relative abundance of Enterococcus, Brevibacterium, Buttiauxella, Pseudomonas, Brevundimonas, and Limnobacter had significant correlations with the concentrations of differential metabolites (e.g., phospholipids and certain amino acids) in insect hemolymph. The antimicrobial compounds secreted by B. subtilis were the primary driving force for the reconstruction of intestinal microbiota. Meanwhile, the altered levels of circulating metabolites in multiple metabolic pathways were potential an adaptive mechanism of insect hosts in response to the shifts of intestinal microbiota. Our findings provided concrete evidence that bacterial intestinal symbiont can alter the physiological state of insects and highlighted the importance of the compositional alterations of intestinal microbiota as a source of variation in circulating metabolites of insect hosts. This article is protected by copyright. All rights reserved.

Analysis of Biosynthetic Gene Clusters, Secretory, and Antimicrobial Peptides Reveals Environmental Suitability of Exiguobacterium profundum PHM11

Halotolerant bacteria produce a wide range of bioactive compounds with important applications in agriculture for abiotic stress amelioration and plant growth promotion. In the present study, 17 biosynthetic gene clusters (BGCs) were identified in Exiguobacterium profundum PHM11 belonging to saccharides, desmotamide, pseudaminic acid, dipeptide aldehydes, and terpene biosynthetic pathways representing approximately one-sixth of genomes. The terpene biosynthetic pathway was conserved in Exiguobacterium spp. while the E. profundum PHM11 genome confirms the presence of the 1-deoxy-d-xylulose 5-phosphate (DXP) pathway for the isopentenyl diphosphate (IPP) synthesis. Further, 2,877 signal peptides (SPs) were identified using the PrediSi server, out of which 592 proteins were prophesied for the secretion having a transmembrane helix (TMH). In addition, antimicrobial peptides (AMPs) were also identified using BAGEL4. The transcriptome analysis of PHM11 under salt stress reveals the differential expression of putative secretion and transporter genes having SPs and TMH. Priming of the rice, wheat and maize seeds with PHM11 under salt stress led to improvement in the root length, root diameters, surface area, number of links and forks, and shoot length. The study shows that the presence of BGCs, SPs, and secretion proteins constituting TMH and AMPs provides superior competitiveness in the environment and make E. profundum PHM11 a suitable candidate for plant growth promotion under salt stress.

Screening of antibacterial activities of Bacillus spp. isolated from the Parangkusumo coastal sand dunes, Indonesia

Background: The emergence of multidrug-resistant bacteria because of poor understanding of the issue and the misuse of antibiotics has become global health concern. Therefore, the discovery of novel antibacterial drugs is urgently needed. New antibacterial compounds may be found in the Bacillus species, which are abundant in sand dune ecosystems. Herein, we examined samples from the Parangkusumo coastal sand dunes in Indonesia.Methods: Samples were collected from three areas in the sand dunes (the area closest to the sea, the core area of sand dunes, and the area farthest from the sea). The samples were inoculated on Luria Bertani agar. Morphological and molecular identification was performed on the basis of 16S rRNA. The samples’ antimicrobial activity was evaluated with the disc diffusion method and compared with that of opportunistic pathogenic bacteria.Results: Five species of Bacillus were successfully isolated from the Parangkusumo coastal sand dunes. To our knowledge, this is the first report of the isolation of Bacillus aryabhattai in Indonesia. All samples showed antimicrobial activity against pathogenic bacteria. B. velezensis and B. subtilis showed antibacterial activity against Gram-positive bacteria, whereas B. aryabhattai and B. megaterium showed antibacterial activity against Gram-negative bacteria, and B. spizizenii showed antibacterial activity toward Gram-positive and Gram-negative bacteria.Conclusion: Five Bacillus species were successfully isolated from the Parangkusumo coastal sand dunes, Indonesia, and all samples showed antimicrobial activity toward opportunistic pathogenic bacteria. The crude antimicrobial compounds from B. megaterium, B. aryabhattai, B. subtilis, and B. spizizenii showed the highest growth-inhibition activity against E. coli, P. aeruginosa, B. cereus, and S. aureus, respectively.

Bacillibactin class of siderophore antibiotics from a marine symbiotic Bacillus as promising antibacterial agents

Preliminary antibacterial metabolite production screening unveiled that B. amyloliquefaciens MTCC 12,713 associated with the intertidal red alga Kappaphycus alverezii exhibited potential inhibitory effects against drug-resistant pathogens methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis, Pseudomonas aeruginosa, and Klebsiella pneumoniae. Four homologous siderophore types of bacillibactins were isolated from a heterotrophic marine bacterium through bioactivity-guided purification. All detectable natural product gene clusters in B. amyloliquefaciens MTCC 12,713 were analyzed by sequencing the complete genome of the bacterium. The studied compounds displayed broad spectrum bactericidal activity against multidrug-resistant strains with a range of minimum inhibitory concentration values from 1.56 to 6.25 µg/mL, whereas standard antibiotic chloramphenicol was active at 6.25 to 12.5 µg/mL. Structure-bioactivity relationship assessment showed that higher electronic values were responsible for antibacterial properties against the nosocomial pathogens. The 2, 3-dihydroxybenzoate (dhb)-assisted biosynthetic pathway of catecholate-enclosed bacillibactins was proposed through the bacillibactin synthase multienzyme complex catalysis followed by dimerization of dhbACEBF operons with 16 genes (~ 12 kb bacterial genome). The present findings recognized an undescribed 4-methoxy-11'-pentanoyloxy-bacillibactin C as a source of potential antibacterial agent for use against drug-resistant pathogens for pharmaceutical applications. KEY POINTS: • Bacillus amyloliquefaciens in association with Kappaphycus alverezii was isolated • Four antibacterial bacillibactin analogs were identified from symbiotic bacterium • 4-Methoxy-11'-pentanoyloxy-bacillibactin C showed potential antibacterial activity.

Ultrasonic and enzymatic pretreatments of Monascus fermentation byproduct for a sustainable production of Bacillus subtilis

BACKGROUND

Monascus fermentation byproduct (MFB) is a biowaste generated after food colorants are extracted. Using MFB to produce probiotics (Bacillus subtilis) is a sustainable way for the entire production to be used as food or animal feed additives. However, due to the rigidity of the Monascus mycelium cell wall, B. subtilis cannot sufficiently utilize the nutrients in MFB, leading to low biomass production efficiency. We studied the effects of ultrasonic treatment, papain, β-glucanase, and chitosanase, and their combinations on improving the levels of soluble components from MFB. The effects of these treatments on mycelium cell walls were visualized using scanning electron microscopy, and their influence on B. subtilis production was analyzed.

RESULTS

Ultrasonic treatment increased the soluble components by 210 g kg^-1 , including 50 g kg^-1 protein and 120 g kg^-1 carbohydrates. An enzyme mixture increased the soluble components by 160 g kg^-1 , including 30 g kg^-1 protein and 90 g kg^-1 carbohydrates. The combination of the two methods achieved the highest increase of soluble components (up to 400 g kg^-1 ) leading to a maximum B. subtilis production of 1 × 10¹¹ colony-forming unit mL^-1 . This yield was about 20 times greater than that using untreated MFB and about eight times greater than treatments using only ultrasonic or enzymatic methods.

CONCLUSION

The productivity of B. subtilis production using MFB as the sole medium can be greatly improved by ultrasound or enzymes, which cause the release of intercellular components or cell wall components. © 2020 Society of Chemical Industry.

Xylan Decomposition in Plant Cell Walls as an Inducer of Surfactin Synthesis by Bacillus subtilis

Hemicellulose is the second most abundant plant heterogenous biopolymer. Among products obtained from a wide range of agro-residues, biosurfactants, e.g., surfactin (SU), are gaining increasing interest. Our previous studies have shown that a Bacillus subtilis strain can successfully produce a significant amount of SU using a rapeseed cake. This work aimed to investigate plant hemicellulose components as substrates promoting SU's efficient production by B. subtilis 87Y. Analyses of SU production, enzymatic activity and cell wall composition of hulled oat caryopses suggest that the main ingredients of plant hemicellulose, in particular xylan and its derivatives, may be responsible for an increased biosurfactant yield.

Molecular Aspects of Plant Growth Promotion and Protection by Bacillus subtilis

Bacillus subtilis is one of the most widely studied plant growth-promoting rhizobacteria. It is able to promote plant growth as well as control plant pathogens through diverse mechanisms, including the improvement of nutrient availability and alteration of phytohormone homeostasis as well as the production of antimicrobials and triggering induced systemic resistance, respectively. Even though its benefits for crop production have been recognized and studied extensively under laboratory conditions, the success of its application in fields varies immensely. It is widely accepted that agricultural application of B. subtilis often fails because the bacteria are not able to persist in the rhizosphere. Bacterial colonization of plant roots is a crucial step in the interaction between microbe and plant and seems, therefore, to be of great importance for its growth promotion and biocontrol effects. A successful root colonization depends thereby on both bacterial traits, motility and biofilm formation, as well as on a signal interplay with the plant. This review addresses current knowledge about plant-microbial interactions of the B. subtilis species, including the various mechanisms for supporting plant growth as well as the necessity for the establishment of the relationship.[Formula: see text] The author(s) have dedicated the work to the public domain under the Creative Commons CC0 "No Rights Reserved" license by waiving all of his or her rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.

Insights into the Current Trends in the Utilization of Bacteria for Microbially Induced Calcium Carbonate Precipitation

Nowadays, microbially induced calcium carbonate precipitation (MICP) has received great attention for its potential in construction and geotechnical applications. This technique has been used in biocementation of sand, consolidation of soil, production of self-healing concrete or mortar, and removal of heavy metal ions from water. The products of MICP often have enhanced strength, durability, and self-healing ability. Utilization of the MICP technique can also increase sustainability, especially in the construction industry where a huge portion of the materials used is not sustainable. The presence of bacteria is essential for MICP to occur. Bacteria promote the conversion of suitable compounds into carbonate ions, change the microenvironment to favor precipitation of calcium carbonate, and act as precipitation sites for calcium carbonate crystals. Many bacteria have been discovered and tested for MICP potential. This paper reviews the bacteria used for MICP in some of the most recent studies. Bacteria that can cause MICP include ureolytic bacteria, non-ureolytic bacteria, cyanobacteria, nitrate reducing bacteria, and sulfate reducing bacteria. The most studied bacterium for MICP over the years is Sporosarcina pasteurii. Other bacteria from Bacillus species are also frequently investigated. Several factors that affect MICP performance are bacterial strain, bacterial concentration, nutrient concentration, calcium source concentration, addition of other substances, and methods to distribute bacteria. Several suggestions for future studies such as CO₂ sequestration through MICP, cost reduction by using plant or animal wastes as media, and genetic modification of bacteria to enhance MICP have been put forward.

Induced resistance in nectarine fruit by Bacillus licheniformis W10 for the control of brown rot caused by Monilinia fructicola

Brown rot caused by Monilinia fructicola has led to considerable preharvest and postharvest losses in all major nectarine fruit-growing areas. In our previous study, we successfully identified a biocontrol strain of bacteria, Bacillus licheniformis W10, that can be used to control brown rot. However, the possible mechanism of the control of brown rot by B. licheniformis W10 is still unclear. Therefore, the objectives of this study were to determine whether B. licheniformis W10 induces resistance by activating defense-related enzymes including antioxidant enzymes in nectarine. Treatment of nectarine fruit with B. licheniformis W10 reduced both M. fructicola-induced oxidative damage and reactive oxygen species (ROS) production. Furthermore, application of B. licheniformis to nectarine fruit resulted in a significant increase in the activity of antioxidant and defense-related enzymes and increase in the expression of the corresponding genes. Overall, our results verified the proposed mechanism of B. licheniformis W10 in controlling M. fructicola via regulation of ROS levels and activation of antioxidant and defense-related enzymes.

CRISPR-dCas9 Mediated Cytosine Deaminase Base Editing in Bacillus subtilis

Base editing technology based on clustered regularly interspaced short palindromic repeats/associated protein 9 (CRISPR/Cas9) is a recent addition to the family of CRISPR technologies. Compared with the traditional CRISPR/Cas9 technology, it does not rely on DNA double strand break and homologous recombination, and can realize gene inactivation and point mutation more quickly and simply. Herein, we first developed a base editing method for genome editing in Bacillus subtilis utilizing CRISPR/dCas9 (a fully nuclease-deficient mutant of Cas9 from S. pyogenes) and activation-induced cytidine deaminase (AID). This method achieved three and four loci simultaneous editing with editing efficiency up to 100% and 50%, respectively. Our base editing system in B. subtilis has a 5 nt editing window, which is similar to previously reported base editing in other microorganisms. We demonstrated that the plasmid curing rate is almost 100%, which is advantageous for multiple rounds of genome engineering in B. subtilis. Finally, we applied multiplex genome editing to generate a B. subtilis 168 mutant strain with eight inactive extracellular protease genes in just two rounds of base editing and plasmid curing, suggesting that it is a powerful tool for gene manipulation in B. subtilis and industrial applications in the future.

The Significance of Bacillus spp. in Disease Suppression and Growth Promotion of Field and Vegetable Crops

Bacillus spp. produce a variety of compounds involved in the biocontrol of plant pathogens and promotion of plant growth, which makes them potential candidates for most agricultural and biotechnological applications. Bacilli exhibit antagonistic activity by excreting extracellular metabolites such as antibiotics, cell wall hydrolases, and siderophores. Additionally, Bacillus spp. improve plant response to pathogen attack by triggering induced systemic resistance (ISR). Besides being the most promising biocontrol agents, Bacillus spp. promote plant growth via nitrogen fixation, phosphate solubilization, and phytohormone production. Antagonistic and plant growth-promoting strains of Bacillus spp. might be useful in formulating new preparations. Numerous studies of a wide range of plant species revealed a steady increase in the number of Bacillus spp. identified as potential biocontrol agents and plant growth promoters. Among different mechanisms of action, it remains unclear which individual or combined traits could be used as predictors in the selection of the best strains for crop productivity improvement. Due to numerous factors that influence the successful application of Bacillus spp., it is necessary to understand how different strains function in biological control and plant growth promotion, and distinctly define the factors that contribute to their more efficient use in the field.

Optimization of laboratory cultivation conditions for the synthesis of antifungal metabolites by bacillus subtilis strains

In order to achieve the optimal number of colony forming units and a high level of antifungal metabolites synthesis, we carried out the periodic cultivation of the Bacillus subtilis BZR 336 g and Bacillus subtilis BZR 517 strains at various pH and temperature levels. In the experiment for determining the optimal temperature, the maximum titer of B. subtilis BZR 336 g bacterium (1.6-1.7 × 109 CFU/ml) was recorded at a cultivation temperature of 20-25 °C. For B. subtilis BZR 517 strain, the temperature turned out to be optimal at 30 °C: the titer was 8.9 × 108 CFU/ml. The maximum antifungal activity of B. subtilis BZR 336 g strain against the test culture of Fusarium oxysporum var. orthoceras was observed at a cultivation temperature of 20-25 °C; for B. subtilis BZR 517 strain, 25-30 °C. When determining the optimal pH level, it was found that a high titer of B. subtilis BZR 336 g strain cells was determined at pH 8.0 (2.7 × 109 CFU/ml), for B. subtilis BZR 517 strain it was at pH 6.0-8.0 (1.0 × 109 CFU/ml). The maximum antifungal activity was noted with the same indicators. Chromatographic and bioautographic analyses suggest that the synthesized antifungal metabolites belong to surfactin and iturin A. The data obtained in this research can be used in the development of the technology for the production of effective biofungicides to protect crops against Fusarium pathogens.

Secondary screening of strains of antagonists to a Phoma pathogen on sunflower

There are presented data of the first stage of the secondary screening of antagonist strains from a collection of the biological methods laboratory of V.S. Pustovoit All-Russian Research Institute of Oil Crops to the aggressive isolate of Phoma macdonaldii Boerema infecting sunflower. We used methods of ‘agar blocks’ and ‘perforated Petri dishes’. As a result of a screening of 55 antagonist strains to Phoma macdonaldii pathogen we selected 17 promising strains-producers of microbiological preparations having biological efficiency exceeding 40.0 %. In control variant without seed treatment sunflower seedlings infection was up to 76.2 %, and maximal biological efficiency of laboratory samples from fungi-producers were determined for a strain M-24 Penicillium sp. (73.8 %); from bacteria of a genus Bacillus – for a strain D-10 Bacillus sp. (74.2%); from bacteria of a genus Pseudomonas – for a strain Sgc-1 Pseudomonas sp. (73.8 %). Maximal colonizing activity were noted for fungi-producers M-24 Penicillium sp. (85.7 %) and Xk-1 Ch. olivaceum (71.4 %), as well as for bacteria of a genus Bacillus – 5B-1 B. subtilis (71.4 %) and a genus Pseudomonas – Oif 2-1 Pseudomonas sp. and 14-3 P. chlororaphis (71.4 %) against Phoma infection in control of 70.0 %.

Short peptides secreted by Bacillus subtilis inhibit the growth of mold on fresh-cut pumpkin (Cucurbita pepo)

BACKGROUND

This study investigates the efficacy of short peptides secreted by Bacillus subtilis for fungal inhibition in fresh-cut pumpkin and for maintaining its shelf life.

RESULTS

Low-molecular-weight filtrate (LC < 1000 Da) of B. subtilis culture (BC) significantly lowered the total number of molds on fresh-cut pumpkin compared with the untreated control and a BC group after storage. Low-molecular-weight filtrate prevented the deterioration of sensory quality in a pumpkin incision, and reduced pectinase activity. It also inhibited the growth of Phytophthora capsici and Penicillium chrysogenum, and the activity of β-1,3-glucan synthase (GS) secreted by both molds. Fifty-seven GS-inhibiting peptides were screened from 95 LC peptides with two to five amino acid residues. The two most potent peptides, AWYW and HWWY, had strongly suppressive effects on the growth of P. capsici and P. chrysogenum.

CONCLUSION

Our study demonstrated that short peptides present in B. subtilis culture can play an important role in the maintenance of fresh-cut pumpkin by suppressing fungal growth. © 2019 Society of Chemical Industry.

Oxygenated elansolid-type of polyketide spanned macrolides from a marine heterotrophic Bacillus as prospective antimicrobial agents against multidrug-resistant pathogens

Three homologous oxygenated elansolid-type of polyketide spanned macrolides were isolated from a heterotrophic marine bacterium, Bacillus amyloliquefaciens MTCC 12716, associated with an intertidal red alga Hypnea valentiae. The complete genome of the bacterium was sequenced and all detectable natural product gene clusters were analysed. The B. amyloliquefaciens MTCC 12716 genome features polyketide synthase (pks) systems of every known formally classified family, nonribosomal peptide synthetases and hybrid clusters. Comprehensive spectroscopic studies revealed the compounds to possess isobenzofuranyl benzoate and 1H-furopyrano[2,3-c]oxacyclononadecine-6-carboxylate moieties. The identified compounds displayed broad-spectrum bactericidal activity against methicillin-resistant Staphylococcus aureus, vancomycin-resistant Enterococcus faecalis, and drug-resistant strains of Pseudomonas aeruginosa and Klebsiella pneumoniae with minimum inhibitory concentrations (MICs) of ≤1.0 µg/mL, whereas the standard antibiotics ampicillin and chloramphenicol were active only at concentrations of ≥6.25 µg/mL. The plausible mechanism of elansolid-type macrolide biosynthesis by trans-AT polyketide synthases through the pks starter unit para-hydroxybenzoic acid was hypothesised, and the structures were correlated with the gene organisation, with the predicted gene cluster comprising 16 genes (~81 kb in size). The best binding poses for each compound with the peptide deformylase (PDF) protein of S. aureus revealed docking scores (>11.30 kcal/mol) greater than actinonin (6.96 kcal/mol), a natural PDF inhibitor. The higher electronic values along with optimum lipophilic parameters support the potential anti-infective properties of the studied macrolides. These antibacterial elansolid-type of polyketide spanned macrolides in marine symbiotic B. amyloliquefaciens could be potential leads for biotechnological and pharmaceutical applications against emerging multidrug-resistant pathogens.

Strategy for the Biosynthesis of Short Oligopeptides: Green and Sustainable Chemistry

Short oligopeptides are some of the most promising and functionally important amide bond-containing components, with widespread applications. Biosynthesis of these oligopeptides may potentially become the ultimate strategy because it has better cost efficiency and environmental-friendliness than conventional solid phase peptide synthesis and chemo-enzymatic synthesis. To successfully apply this strategy for the biosynthesis of structurally diverse amide bond-containing components, the identification and selection of specific biocatalysts is extremely important. Given that perspective, this review focuses on the current knowledge about the typical enzymes that might be potentially used for the synthesis of short oligopeptides. Moreover, novel enzymatic methods of producing desired peptides via metabolic engineering are highlighted. It is believed that this review will be helpful for technological innovation in the production of desired peptides.

Bioactive Secondary Metabolites from Bacillus subtilis: A Comprehensive Review

Bacillus subtilis is widely underappreciated for its inherent biosynthetic potential. This report comprehensively summarizes the known bioactive secondary metabolites from B. subtilis and highlights potential applications as plant pathogen control agents, drugs, and biosurfactants. B. subtilis is well known for the production of cyclic lipopeptides exhibiting strong surfactant and antimicrobial activities, such as surfactins, iturins, and fengycins. Several polyketide-derived macrolides as well as nonribosomal peptides, dihydroisocoumarins, and linear lipopeptides with antimicrobial properties have been reported, demonstrating the biosynthetic arsenal of this bacterium. Promising efforts toward the application of B. subtilis strains and their natural products in areas of agriculture and medicine are underway. However, industrial-scale availability of these compounds is currently limited by low fermentation yields and challenging accessibility via synthesis, necessitating the development of genetically engineered strains and optimized cultivation processes. We hope that this review will attract renewed interest in this often-overlooked bacterium and its impressive biosynthetic skill set.

A Review of the Microbial Production of Bioactive Natural Products and Biologics

A variety of organisms, such as bacteria, fungi, and plants, produce secondary metabolites, also known as natural products. Natural products have been a prolific source and an inspiration for numerous medical agents with widely divergent chemical structures and biological activities, including antimicrobial, immunosuppressive, anticancer, and anti-inflammatory activities, many of which have been developed as treatments and have potential therapeutic applications for human diseases. Aside from natural products, the recent development of recombinant DNA technology has sparked the development of a wide array of biopharmaceutical products, such as recombinant proteins, offering significant advances in treating a broad spectrum of medical illnesses and conditions. Herein, we will introduce the structures and diverse biological activities of natural products and recombinant proteins that have been exploited as valuable molecules in medicine, agriculture and insect control. In addition, we will explore past and ongoing efforts along with achievements in the development of robust and promising microorganisms as cell factories to produce biologically active molecules. Furthermore, we will review multi-disciplinary and comprehensive engineering approaches directed at improving yields of microbial production of natural products and proteins and generating novel molecules. Throughout this article, we will suggest ways in which microbial-derived biologically active molecular entities and their analogs could continue to inspire the development of new therapeutic agents in academia and industry.

Bacillus subtilis: A plant-growth promoting rhizobacterium that also impacts biotic stress

Plants encounter many biotic agents, such as viruses, bacteria, nematodes, weeds, and arachnids. These entities induce biotic stress in their hosts by disrupting normal metabolism, and as a result, limit plant growth and/or are the cause of plant mortality. Some biotic agents, however, interact symbiotically or synergistically with their host plants. Some microbes can be beneficial to plants and perform the same role as chemical fertilizers and pesticides, acting as a biofertilizer and/or biopesticide. Plant growth promoting rhizobacteria (PGPR) can significantly enhance plant growth and represent a mutually helpful plant-microbe interaction. Bacillus species are a major type of rhizobacteria that can form spores that can survive in the soil for long period of time under harsh environmental conditions. Plant growth is enhanced by PGPR through the induction of systemic resistance, antibiosis, and competitive omission. Thus, the application of microbes can be used to induce systemic resistance in plants against biotic agents and enhance environmental stress tolerance. Bacillus subtilis exhibits both a direct and indirect biocontrol mechanism to suppress disease caused by pathogens. The direct mechanism includes the synthesis of many secondary metabolites, hormones, cell-wall-degrading enzymes, and antioxidants that assist the plant in its defense against pathogen attack. The indirect mechanism includes the stimulation of plant growth and the induction of acquired systemic resistance. Bacillus subtilis can also solubilize soil P, enhance nitrogen fixation, and produce siderophores that promote its growth and suppresses the growth of pathogens. Bacillus subtilis enhances stress tolerance in their plant hosts by inducing the expression of stress-response genes, phytohormones, and stress-related metabolites. The present review discusses the activity of B. subtilis in the rhizosphere, its role as a root colonizer, its biocontrol potential, the associated mechanisms of biocontrol and the ability of B. subtilis to increase crop productivity under conditions of biotic and abiotic stress.

Overview of the Antimicrobial Compounds Produced by Members of the Bacillus subtilis Group

Over the last seven decades, applications using members of the Bacillus subtilis group have emerged in both food processes and crop protection industries. Their ability to form survival endospores and the plethora of antimicrobial compounds they produce has generated an increased industrial interest as food preservatives, therapeutic agents and biopesticides. In the growing context of food biopreservation and biological crop protection, this review suggests a comprehensive way to visualize the antimicrobial spectrum described within the B. subtilis group, including volatile compounds. This classification distinguishes the bioactive metabolites based on their biosynthetic pathways and chemical nature: i.e., ribosomal peptides (RPs), volatile compounds, polyketides (PKs), non-ribosomal peptides (NRPs), and hybrids between PKs and NRPs. For each clade, the chemical structure, biosynthesis and antimicrobial activity are described and exemplified. This review aims at constituting a convenient and updated classification of antimicrobial metabolites from the B. subtilis group, whose complex phylogeny is prone to further development.

Antifungal Activity of Lipopeptides From Bacillus XT1 CECT 8661 Against Botrytis cinerea

This work aims to explore the capacity of a Bacillus methylotrophicus (later heterotypic synonym of Bacillus velezensis) strain named XT1 CECT 8661 against the necrotrophic plant pathogen Botrytis cinerea and to identify the compounds responsible for its activity. Q_TOF electrospray mass spectrometry analysis allows us to detect several lipopeptides – surfactin, bacillomycin, and fengycin – in XT1 cultures. In vitro antibiosis studies demonstrated the efficiency of the lipopeptide fraction for the inhibition of fungal growth. In fact, microscopy studies (SEM/TEM) revealed, an alteration of the morphology of the phytopathogen in interaction with lipopeptides, with resistance structures appearing in the early stages of growth of the fungus. Our studies, carried out with tomatoes, grapes, and strawberries have demonstrated the efficiency of Bacillus XT1 CECT 8661 lipopeptides against B. cinerea infection and it capability to trigger the antioxidant activity in fruit. Overall, the results of this study highlight the potential of lipopeptides of this strain as an effective biological control agent against the colonisation of B. cinerea.

Structural identification of lipopeptide biosurfactants produced by Bacillus subtilis strains grown on the media obtained from renewable natural resources

The aim of the study was to identify and characterize lipopeptide (LP) biosurfactants produced by two Bacillus subtilis strains (KP7 and I'-1a) grown on various media prepared from renewable natural resources: two different brewery wastewaters (BW#4 and BW#6), 2% beet molasses (M), apple peels extract (APE) supplemented with 0.25% of yeast extract (YE) or 0.25% peptone (P), and similarly supplemented carrot peels extract (CPE). In all used media both strains retained their individual LP production signature characterized by surfactin and iturin overproduction exhibited by KP7 and I'-1a strain, respectively. The production level and the structural diversity of synthesized LPs were dependent on the medium composition. In the CPE+YE medium it was higher than the yield obtained in Luria-Bertani (140.6 and 100.3 mg L^-1, respectively). Surfactins were produced by both strains as a mixture of four homologues (C13-C16) with the domination of variant C14. All other broths prepared from renewable resources strongly stimulated the iturin production by I'-1a strain with the exception of BW media. The highest iturin concentration (428.7 mg L^-1) obtained in the CPE+P culture of I'-1a strain was about seven-fold higher than in LB. In all cultures only iturin A was identified. Among four iturin homologues (C13-16) produced by I'-1a strain, the highest relative contents of C16 variant (70-80%) were calculated for samples obtained from APE+P and CPE+P media. The obtained data indicate that the waste composition has an influence on both the types and amounts of biosurfactants produced by studied B. subtilis strains.