Effects of Bacillus subtilis on Cucumber Seedling Growth and Photosynthetic System under Different Potassium Ion Levels

Potassium deficiency is one of the important factors restricting cucumber growth and development. This experiment mainly explored the effect of Bacillus subtilis (B. subtilis) on cucumber seedling growth and the photosynthetic system under different potassium levels, and the rhizosphere bacteria (PGPR) that promote plant growth were used to solubilize potassium in soil, providing theoretical support for a further investigation of the effect of biological bacteria fertilizer on cucumber growth and potassium absorption. "Xinjin No. 4" was used as the test material for the pot experiment, and a two-factor experiment was designed. The first factor was potassium application treatment, and the second factor was bacterial application treatment. The effects of different treatments on cucumber seedling growth, photosynthetic characteristics, root morphology, and chlorophyll fluorescence parameters were studied. The results showed that potassium and B. subtilis had obvious promotion effects on the cucumber seedling growth and the photosynthesis of leaves. Compared with the blank control, the B. subtilis treatment had obvious effects on the cucumber seedling height, stem diameter, leaf area, total root length, total root surface area, total root volume, branch number, crossing number, gs, WUE, Ci, and A; the dry weight of the shoot and root increased significantly (p ≤ 0.05). Potassium application could significantly promote cucumber growth, and the effect of B. subtilis and potassium application was greater than that of potassium application alone, and the best effect was when 0.2 g/pot and B. subtilis were applied. In conclusion, potassium combined with B. subtilis could enhance the photosynthesis of cucumber leaves and promote the growth of cucumber.

Bacillus methylotrophicus DCS1: Production of Different Lipopeptide Families, In Vitro Antifungal Activity and Suppression of Fusarium Wilt in Tomato Plants

The present work aims to quantitatively and qualitatively monitor the production of lipopeptide mixtures by Bacillus methylotrophicus DCS1 strain in Landy medium and to investigate the antifungal activities of DCS1 strain and its produced lipopeptides. The in vitro activities were tested by the direct confrontation and agar well diffusion methods, while the in vivo study was carried out in order to test the efficiency of DCS1 bacterial suspension in the control of Fusarium wilt in tomato plants. Identification of lipopeptides by mass spectrometry (LC/MSD-TOF) showed that lipopeptide isoforms produced during the first 24 h and 48 h of fermentation are identical, belonging to bacillomycin D and fengycins A and B homologues with a difference in the yield of production. After 72 h of fermentation corresponding to the end of incubation period, B. methylotrophicus DCS1 is able to produce a mixture of surfactin, pumilacidin, iturin A/mycosubtilin, iturin C1, bacillomycin D and fengycins A and B isoforms. The results of in vitro antifungal experiments suggest that B. methylotrophicus DCS1 has a significant potential as a biocontrol agent, owing to lipopeptides produced, endowed with antifungal activity against several phytopathogenic fungi. The curative treatment of tomato plants with DCS1 bacterial suspension was more effective in the protection against Fusarium oxysporum f. sp. radicis-lycopersici (FORL) than the preventive treatment by comparing the average number of leaves remaining healthy after 30 days of each treatment and the appearance of tomato plants roots. The results indicate that B. methylotrophicus DCS1 exhibit a significant suppression of Fusarium wilt symptoms in tomato plants comparable to that of commercial fungicides and could be an alternative to chemically synthesized pesticides.

Iturin: A Promising Cyclic Lipopeptide with Diverse Applications

This comprehensive review examines iturin, a cyclic lipopeptide originating from Bacillus subtilis and related bacteria. These compounds are structurally diverse and possess potent inhibitory effects against plant disease-causing bacteria and fungi. Notably, Iturin A exhibits strong antifungal properties and low toxicity, making it valuable for bio-pesticides and mycosis treatment. Emerging research reveals additional capabilities, including anticancer and hemolytic features. Iturin finds applications across industries. In food, iturin as a biosurfactant serves beyond surface tension reduction, enhancing emulsions and texture. Biosurfactants are significant in soil remediation, agriculture, wound healing, and sustainability. They also show promise in Microbial Enhanced Oil Recovery (MEOR) in the petroleum industry. The pharmaceutical and cosmetic industries recognize iturin's diverse properties, such as antibacterial, antifungal, antiviral, anticancer, and anti-obesity effects. Cosmetic applications span emulsification, anti-wrinkle, and antibacterial use. Understanding iturin's structure, synthesis, and applications gains importance as biosurfactant and lipopeptide research advances. This review focuses on emphasizing iturin's structural characteristics, production methods, biological effects, and applications across industries. It probes iturin's antibacterial, antifungal potential, antiviral efficacy, and cancer treatment capabilities. It explores diverse applications in food, petroleum, pharmaceuticals, and cosmetics, considering recent developments, challenges, and prospects.

Enhancing Stevia rebaudiana growth and yield through exploring beneficial plant-microbe interactions and their impact on the underlying mechanisms and crop sustainability

Stevia rebaudiana is an important medicinal plant which represents the most important sugar substitute in many countries. Poor seed germination of this plant is a critical problem that affects the final yield and the availability of the products in the market. Continuous cropping without supplying soil nutrients is also a serious issue as it results in declining soil fertility. This review highlights the important use of beneficial bacteria for the enhancement of Stevia rebaudiana growth and its dynamic interactions in the phyllosphere, rhizosphere, and endosphere. Fertilizers can increase crop yield and preserve and improve soil fertility. There is a rising concern that prolonged usage of chemical fertilizers may have negative impacts on the ecosystem of the soil. On the other hand, soil health and fertility are improved by plant growth-promoting bacteria which could eventually increase plant growth and productivity. Accordingly, a biocompatible strategy involving beneficial microorganisms inoculation is applied to boost plant growth and reduce the negative effects of chemical fertilizers. Plants benefit extensively from endophytic bacteria, which promote growth and induce resistance to pathogens and stresses. Additionally, several plant growth-promoting bacteria are able to produce amino acids, polyamines, and hormones that can be used as alternatives to chemicals. Therefore, understanding the dynamic interactions between bacteria and Stevia can help make the favorable bacterial bio-formulations, use them more effectively, and apply them to Stevia to improve yield and quality.

Transcriptome and metabolome analyses reveal that Bacillus subtilis BS-Z15 lipopeptides mycosubtilin homologue mediates plant defense responses

Microbial-plant interactions protect plants from external stimuli, releasing various elicitor that activate the plants defense response and regulate its growth. Bacillus subtilis BS-Z15 was screened from cotton inter-rhizosphere soil, antagonized various plant pathogens, and protected cotton against Verticillium dahliae. This study showed that the BS-Z15 lipopeptide mycosubtilin homologue could act as an elicitor to induce systemic resistance (ISR) in plants. Mycosubtilin homologue induced ROS burst and deposition, callose deposition, MAPK cascade phosphorylation, and up-regulated PR1 and PDF1.2 gene expression in Arabidopsis seedlings, moreover enhanced resistance of Arabidopsis to Pseudomonas syringae pv. Tomato DC3000 (Pst DC3000) and V. dahliae. Transcriptome analysis was then used to evaluate the impact of mycosubtilin homologue on plant gene expression control. Mycosubtilin homologues activated Arabidopsis ISR on genes in metabolic pathways such as Arabidopsis plant-pathogen interactions, phenylpropanoid biosynthesis, MAPK signaling pathway, and phytohormone signaling. These analyses revealed that mycosubtilin homologues mediate the regulation of plant systemic resistance and growth and development by affecting related metabolites in glycolysis and gluconeogenesis, pentose phosphate pathway, tricarboxylic acid cycle, and amino acid metabolism in Arabidopsis. These findings confirmed that a mycosubtilin homologue could trigger the initiation of the Arabidopsis ISR by interacting with a variety of PTI components and transcriptional metabolic signaling pathways.

Maize Root Exudates Recruit Bacillus amyloliquefaciens OR2-30 to Inhibit Fusarium graminearum Infection

Bacillus spp. can exert plant growth-promoting effects and biocontrol effects after effective colonization, and bacterial chemotaxis toward plant root exudates is the initial step to colonize. Under biotic stress, plants are able to alter their root exudates to attract or avoid different types of microbes. Hence, Bacillus chemotaxis toward root exudates after pathogen infection is crucial for exerting their beneficial effects. In this study, the Bacillus amyloliquefaciens OR2-30 strain, which exhibited greater chemotaxis ability toward maize root exudates after Fusarium graminearum infection, was screened from 156 rhizosphere microorganisms. The infected maize root exudates were further confirmed to improve the swarming and biofilm formation ability of the OR2-30 strain. Chemotaxis, swarming, and biofilm formation ability were able to influence bacterial colonization. Indeed, the the OR2-30 strain displayed more effective colonization ability in the maize rhizosphere after F. graminearum inoculation. Moreover, lipopeptides produced by OR2-30 were identified as iturins and responsible for suppressing F. graminearum growth. Further study showed that lipopeptides suppressed the growth of F. graminearum by inhibiting conidia formation and germination, inducing reactive oxygen species production and causing cell death in mycelium. Eventually, the OR2-30 strain increased maize resistance against F. graminearum. These results suggested that maize root exudates could recruit B. amyloliquefacines OR2-30 after F. graminearum infection, and that OR2-30 then suppresses the F. graminearum by producing lipopeptides, such as iturins, to protect maize.

Biocontrol of Phyllosticta citricarpa by Bacillus spp.: biological and chemical aspects of the microbial interaction

Citrus fruits are the most produced fruits in the world, but they are threatened by several pathogens, including the fungus Phyllosticta citricarpa, the causal agent of citrus black spot (CBS). The fungus affects most citrus species and the infection results in economic losses in citrus-producing areas. This disease causes the aesthetic depreciation of fresh fruit, impairing its commercialization. As an alternative to the use of synthetic fungicides to control the pathogen, the biological control, using bacteria of the genus Bacillus, is highlighted. Such microorganisms enable biocontrol by the production of volatile organic compounds (VOC) or non-volatile. Therefore, this work aimed to evaluate the production of VOC by isolates of Bacillus spp. grown in different culture media; to evaluate the effects of these compounds on the evolution of CBS lesions in orange fruits; to study the effects of VOC on resistance induction in orange fruits; to evaluate the effects of VOC on P. citricarpa morphology in CBS lesions, and to identify the produced VOC. Tryptone soya agar (TSA) and tryptone soya broth (TSB) media used to culture the bacterium resulted in up to 73% pathogen inhibition by VOC. Volatile compounds from Bacillus spp. ACB-65 and Bacillus spp. ACB-73 when cultured in TSB culture medium provided 86% inhibition of freckles that evolved to hard spots. The volatile fractions produced by the bacteria were identified as alcohols, ketones, amines, ethers, aldehydes and carboxylic acids that can serve as arsenal against the phytopathogen. The present work demonstrated the potential of VOC produced by Bacillus spp. in the control of P. citricarpa.

Effects of Bacillus subtilis iturin A on HepG2 cells in vitro and vivo

Iturin A with cyclic peptide and fatty acid chain isolated from Bacillus subtilis fermentation shows a variety of biological activities. Among them, the anticancer activity attracted much attention. However, the molecular mechanism of its inhibitory effect on hepatocellular carcinoma was still unclear. Thus its effect on hepatocellular carcinoma was tested in this research. It was found that iturin A could enter HepG2 cells immediately and cause reactive oxygen species burst, disrupt cell cycle and induce apoptosis, paraptosis and autophagy in vitro. The iturin A without fatty acid chain showed no antitumor activity. Amphiphilic is critical to the activity of iturin A. The anticancer activity of iturin A to hepatocellular carcinoma was also verified in mice models carrying xenograft tumors constructed by HepG2 cells. At a dosage of 3 mg/kg/day, iturin A significantly inhibited the further increase of the tumor weight by 58.55%, and reduced the expression of Ki67 in tumor. In the tumor treated with iturin A, lymphocyte infiltration was found, and the expressions of TGF-β1and PD-L1 were decreased, which indicated that the tumor immune microenvironment was improved. Besides, iturin A showed no significant harm on the health of mice except slight disturbance of liver function. These results suggested that iturin A had significant antitumor effect in vitro and vivo, and provide a basis for the application of iturin A as anticancer agent.

Profiling of Metabolites of Bacillus spp. and Their Application in Sustainable Plant Growth Promotion and Biocontrol

Bacillus spp. are well-characterized as efficient bioinoculants for sustainable plant growth promotion and biocontrol of phytopathogens. Members of this spp. exhibit the multifaceted beneficial traits that are involved in plant nutrition and antimicrobial activities against phytopathogens. Keeping in view their diverse potential, this study targeted the detailed characterization of three root-colonizing Bacillus strains namely B. amyloliquefaciens, B. subtilis, and B. tequilensis, characterized based on 16S rRNA sequencing homology. The strains exhibited better plant growth promotion and potent broad-spectrum antifungal activities and exerted 43–86% in-vitro inhibition of growth of eight fungal pathogens. All strains produced indole acetic acid (IAA) in the range of 0.067–0.147 μM and were positive for the production of extracellular enzymes such as cellulase, lipase, and protease. Ultra-performance Liquid Chromatography-Electrospray Ionization-Mass Spectrometry (UPLC-ESI-MS/MS) analysis revealed the production of antifungal metabolites (AFMs) such as surfactins, iturins, fengycins, macrolactins, bacillomycin-D, and catechol-based siderophore bacillibactin which were further confirmed by amplifying the genes involved in the biosynthesis of these antimicrobial lipopeptides. When compared for the amounts of different cyclic-peptides produced by three Bacillus strains, B. amyloliquefaciens SB-1 showed the most noticeable amounts of all the antifungal compounds. Plant experiment results revealed that inoculation with phytohormone producing Bacillus spp. strains demonstrated substantial growth improvement of wheat biomass, number of spikes, and dry weight of shoots and roots. Results of this study indicate the biocontrol and biofertilizer potential of Bacillus spp. for sustainable plant nutrient management, growth promotion, and effective biocontrol of crop plants, particularly cultivated in the South Asian region.

Mecanismos de acción de <i>Bacillus</i> spp. (Bacillaceae) contra microorganismos fitopatógenos durante su interacción con plantas

Algunos Bacillus spp. promotores de crecimiento vegetal son microorganismos reconocidos como agentes de control biológico que forman una estructura de resistencia denominada endospora, que les permite sobrevivir en ambientes hostiles y estar en casi todos los agroecosistemas. Estos microorganismos han sido reportados como alternativa al uso de agroquímicos. Sus mecanismos de acción se pueden dividir en: producción de compuestos antimicrobianos, como son péptidos de síntesis no ribosomal (NRPs) y policétidos (PKs); producción de hormonas, capacidad de colonización, formación de biopelículas y competencia por espacio y nutrientes; síntesis de enzimas líticas como quitinasas, glucanasas, protesasas y acil homoserin lactonasas (AHSL); producción de compuestos orgánicos volátiles (VOCs); e inducción de resistencia sistémica (ISR). Estos mecanismos han sido reportados en la literatura en diversos estudios, principalmente llevados a cabo a nivel in vitro. Sin embargo, son pocos los estudios que contemplan la interacción dentro del sistema tritrófico: planta – microorganismos patógenos – Bacillus sp. (agente biocontrolador), a nivel in vivo. Es importante destacar que la actividad biocontroladora de los Bacillus es diferente cuando se estudia bajo condiciones de laboratorio, las cuales están sesgadas para lograr la máxima expresión de los mecanismos de acción. Por otra parte, a nivel in vivo, la interacción con la planta y el patógeno juegan un papel fundamental en la expresión de dichos mecanismos de acción, siendo esta más cercana a la situación real de campo. Esta revisión se centra en los mecanismos de acción de los Bacillus promotores de crecimiento vegetal, expresados bajo la interacción con la planta y el patógeno.

The Mode of Action of Bacillus Species against Fusarium graminearum, Tools for Investigation, and Future Prospects

Fusarium graminearum is a pervasive plant pathogenic fungal species. Biological control agents employ various strategies to weaken their targets, as shown by Bacillus species, which adopt various mechanisms, including the production of bioactive compounds, to inhibit the growth of F. graminearum. Various efforts to uncover the antagonistic mechanisms of Bacillus against F. graminearum have been undertaken and have yielded a plethora of data available in the current literature. This perspective article attempts to provide a unified record of these interesting findings. The authors provide background knowledge on the use of Bacillus as a biocontrol agent as well as details on techniques and tools for studying the antagonistic mechanism of Bacillus against F. graminearum. Emphasizing its potential as a future biological control agent with extensive use, the authors encourage future studies on Bacillus as a useful antagonist of F. graminearum and other plant pathogens. It is also recommended to take advantage of the newly invented analytical platforms for studying biochemical processes to understand the mechanism of action of Bacillus against plant pathogens in general.

Rhizospheric Bacillus subtilis Exhibits Biocontrol Effect against Rhizoctonia solani in Pepper (Capsicum annuum)

This study aimed at evaluating the ability of SL-44 to control Rhizoctonia solani and promote pepper (Capsicum annuum) growth. Strain SL-44 was isolated from plant rhizosphere and the pot experiment results indicated that the dry and fresh weights of pepper in SL-44 and Rhizoctonia solani (S-R) treatment were 45.5% and 54.2% higher than those in Rhizoctonia solani (R) treatment and 18.2% and 31.8% higher than those in CK (control, noninoculation) treatment. The plant height in S-R treatment increased by 14.2% and 9.0% compared with those in the R and CK treatments, respectively. In vitro antagonism assay showed that SL-44 exhibited strong antifungal activity against the mycelial growth of Rhizoctonia solani, with an inhibition rate of 42.3%. The amount of phosphorus dissolved by SL-44 reached 60.58 mg·L^-1 in broth and 7.5 μg·mL^-1 IAA were secreted by SL-44. Strain SL-44 inhibited the growth of R. solani and improved biomass of pepper plants. Mass exchange and information transmission between the pepper plants and SL-44 mutually promoted their development. Bacillus subtilis SL-44 has a great potential as biocontrol agent against Rhizoctonia solani on pepper plants.

Complete Genome Sequence of Bacillus subtilis GQJK2, a Plant Growth-Promoting Rhizobacterium with Antifungal Activity

Bacillus subtilis GQJK2 is a plant growth-promoting rhizobacterium with antifungal activity which was isolated from Lycium barbarum L. rhizosphere. Here, we report the complete genome sequence of B. subtilis GQJK2. Ten gene clusters involved in the biosynthesis of antagonistic compounds were predicted.