Bacillus velezensis strain MBY2, a potential agent for the management of crown gall disease

Biocontrol of Crown Gall Disease of Cherry Trees by Bacillus velezensis

Crown gall disease (CGD), caused by Agrobacterium tumefaciens, is a common plant disease that leads to significant economic losses. Biological control is a sustainable and scalable method for managing CGD. In this study, we isolated three Bacillus strains from the rhizosphere soil of healthy cherry trees and investigated their biocontrol activities and the underlying mechanisms against CGD of cherry trees. The results demonstrate that the three Bacillus strains can effectively inhibit the growth of the pathogenic A. tumefaciens strain XYT58 in vitro under different culture conditions. The pot experiments showed that the three strains could prevent CGD in cherry seedlings. Using PCR amplification, we identified the genes responsible for the synthesis of difficidin, macrolactin, and bacilysin in the three strains. In addition, inoculation with strains WY66 and WY519 significantly enhanced the expression of JA, ET, and SA pathway-related genes in cherry plants. The presence of antibiotic synthesis-related genes in the Bacillus strains and the trigger of plant ISR may explain their ability to control CGD in cherry trees. The findings of this study provide a theoretical basis for the application and development of plant growth-promoting rhizobacteria Bacillus strains in the control of CGD.

Bacillus lumedeiriae sp. nov., a Gram-Positive, Spore-Forming Rod Isolated from a Pharmaceutical Facility Production Environment and Added to the MALDI Biotyper® Database

A Gram-positive, aerobic, rod-shaped and spore-forming bacterium strain designation, B190/17, was isolated from an air monitoring sample of a Brazilian immunobiological production facility in 2017. The strain was not identifiable by biochemical methodology VITEK® 2 or by MALDI-TOF MS with VITEK® MS RUO and MALDI Biotyper®. The 16S rRNA gene sequencing results showed 98.51% similarity with Bacillus wudalianchiensis FJAT 27215T, 98.28% with 'Bacillus aerolatus' CX 253T, 97.96% with Bacillus badius MTCC 1458T, 97.63% with Bacillus xiapuensis FJAT 46582T and 97.21% with Bacillus thermotolerans SGZ8T. Biochemical data showed that the strain was alanine arylamidase-, Ala-Phe-Pro arylamidase-, ELLMAN (cysteine residues)-, leucine arylamidase-, phenyalanine arylamidase- and tyrosine arylamidase-positive. The genomic DNA G+C% content of B190/17 was 41.6 mol%. The phylogenetic, genomic taxonomy and biochemical tests suggested that B190/17 represents a novel species and should be classified as the type strain of a novel Bacillus species. The name Bacillus lumedeiriae sp. nov. was proposed. After characterization, B190/17 was added to the MALDI Biotyper® database as Bacillus lumedeiriae sp. nov.

Evaluation of Chemical and Biological Products for Control of Crown Gall on Rose

Crown gall is a soil-borne bacterial disease caused by Agrobacterium tumefaciens, leading to significant economic losses in many plant species. For the assessment of the biological and chemical products on crown gall, each plant's crown region and roots were wounded, and then were dipped into their respective treatments. After the treatments, the plants were inoculated with a suspension of pathogenic A. tumefaciens isolate FBG1034 and maintained in a greenhouse for six months to assess them for gall formation. A quantitative real-time PCR assay was performed to quantify the A. tumefaciens using the chvE gene. Biological products such as the Agrobacterium radiobacter strain K1026, and strains 1 and 2, resulted in the lowest average root gall diameter and significantly reduced the crown gall diameter to stem diameter ratio, and the chemical product copper octanoate reduced the number of crown and root galls as well as the crown and root gall diameter compared to the inoculated, non-treated control. Moreover, both the A. radiobacter strain K1026 and strain 1 treatments resulted in an approximately 85% and 65% reduction in crown and root gall incidence, respectively, in both of the trials compared to the inoculated, non-treated plants. The findings of this study indicate that the use of biological and chemical products could help to suppress crown and root gall disease in rose plants.

Bacillus subtilis SPB1 lipopeptide biosurfactant: antibacterial efficiency against the phytopathogenic bacteria Agrobacterium tumefaciens and compared production in submerged and solid state fermentation systems

Bacillus subtilis SPB1 derived biosurfactants (BioS) proved its bio-control activity against Agrobacterium tumefaciens using tomato plant. Almost 83% of disease symptoms triggered by Agrobacterium tumefaciens were reduced. Aiming potential application, we studied lipopeptide cost-effective production in both fermentations systems, namely the submerged fermentation (SmF) and the solid-state fermentation (SSF) as well as the use of Aleppo pine waste and confectionery effluent as cheap substrates. Optimization studies using Box-Behnken (BB) design followed by the analysis with response surface methodology were applied. When using an effluent/sea water ratio of 1, Aleppo pine waste of 14.08 g/L and an inoculum size of 0.2, a best production yield of 17.16 ± 0.91 mg/g was obtained for the SmF. While for the SSF, the best production yield of 27.59 ± 1.63 mg/g was achieved when the value of Aleppo pine waste, moisture, and inoculum size were, respectively, equal to 25 g, 75%, and 0.2. Hence, this work demonstrated the superiority of SSF over SmF.

Native Bacillus paralicheniformis isolate as a potential agent for phytopathogenic nematodes control

Phytopathogenic nematodes (PPNs) are responsible for substantial damages within agricultural crops worldwide which can be controlled employing beneficial microorganisms and/or their metabolites in an ecofriendly way. Nevertheless, the success of the control regards not only on the virulence of the strains or the toxicity of their metabolites but also on their ability to colonize and remain in the rhizospheric environment, particularly in those crops affected by abiotic stresses promoted by the climate change. Consequently, the bioprospection of beneficial microorganisms able to control PPNs and to thrive in adverse conditions has attracted attention. On this way, deserts are perfect ecological niches to isolate microorganisms adapted to harsh enviroments. The purpose of this research was to isolate and characterize bacteria from rhizospheric soil samples collected in the Northwestern Desert of Mexico with potential for PPNs control. As first screening, secretomes of each isolate were tested in vitro for nematicidal activity (NA). Then, activities from secretomes and endospores from the selected isolate were confirmed in vivo assays. From 100 thermotolerant isolates, the secretome of the isolate identified as Bacillus paralicheniformis TB197 showed the highest NA (>95%) against Meloidogyne incognita, both in vitro and in vivo tests, suppressing infections caused by M. enterolobii in tomato crops, too. In open field tests, the endospores of TB197 strain showed a reduction of 81% in the infection severity caused by M. enterolobii (p ≤ 0.05), while the galling index (GI) was reduced 84% (p ≤ 0.05) in tomato greenhouse-tests. Also, a reduction of the root necrosis (81%) caused by Radopholus similis in banana plantations (p ≤ 0.05), compared to the control was observed. Owing to their efficacy in controlling PPNs infections, the endospores and secondary metabolites of B. paralicheniformis TB197 strain could be used in bionematicidal formulations.

Bacillus velezensis FX-6 suppresses the infection of Botrytis cinerea and increases the biomass of tomato plants

Botrytis cinerea causing tomato gray mold is a major cause of economic loss in tomato production. It is urgent and necessary to seek an effective and environmentally friendly control strategy to control tomato grey mold disease. In this study, Bacillus velezensis FX-6 isolated from the rhizosphere of plants displayed significant inhibitory ability against B. cinerea and could promote tomato plant growth. FX-6 could effectively inhibit the growth of Botrytis cinerea mycelium in vitro and in vivo, and the inhibitory rate in vitro could reach 78.63%. According to morphological observations and phylogenetic trees based on sequences of the 16S rDNA and gyrA (DNA gyrase subunit A) genes, the strain FX-6 was identified as Bacillus velezensis. In addition, B. velezensis FX-6 showed antagonistic activity against seven phytopathogens, this indicated that FX-6 had broad-spectrum biocontrol activity. We also found that FX-6 fermentation broth had the strongest antagonistic activity against B. cinerea when the culture time was 72 hours, and the inhibition rate was 76.27%. The growth promotion test revealed that strain FX-6 significantly promoted tomato seed germination and seedling growth. Further deeply study on growth-promoting mechanism indicated that the FX-6 produced IAA and siderophore, and had ACC deaminase activity. The trait of significant biological control activity and growth promoting effect on tomato imply that B. velezensis FX-6 has the potential to be used as a biocontrol agent for tomato gray mold management.

Isolation and Identification of Bacteria of Genus Bacillus from Composting Urban Solid Waste and Palm Forest in Northern Peru

A technical challenge for composting in Peruvian cities with annual temperatures below 20 °C is that the degradation of municipal solid waste (MSW) is slow, so the identification of cold-adapted bacteria would be interesting for use as inoculants in places with these climatic conditions. This study isolated, identified, and evaluated bacterial strains with cellulolytic and amylolytic activities at low temperatures. Bacterial strains were isolated from the Chachapoyas Municipal Composting Plant and soil from the Ocol Palm Forest in northern Peru. The screening was carried out to evaluate the extracellular enzyme activity of the strains at low temperatures, grouping those with cellulolytic and cellulolytic/amylolytic activities. The DNA-barcoding using 16S rRNA and enzyme activity allowed the identification and selection of five species with enzymatic activity at 15 and 20 °C of the genus Bacillus, three with cellulolytic/amylolytic activity (B. wiedmanii, B. subtilis, and B. velezensis), and two with cellulolytic activity (B. safensis subsp. safensis, and B. subtilis). These strains showed tolerance to temperatures below optimum and could be used in further studies as inoculants for composting organic wastes at temperatures below 20 °C.

Impact of Cumulative Environmental and Dietary Xenobiotics on Human Microbiota: Risk Assessment for One Health

Chemical risk assessment in the context of the risk analysis framework was initially designed to evaluate the impact of hazardous substances or xenobiotics on human health. As the need of multiple stressors assessment was revealed to be more reliable regarding the occurrence and severity of the adverse effects in the exposed organisms, the cumulative risk assessment started to be the recommended approach. As toxicant mixtures and their "cocktail effects" are considered to be main hazards, the most important exposure for these xenobiotics would be of dietary and environmental origin. In fact, even a more holistic prism should currently be considered. In this sense, the definition of One Health refers to simultaneous actions for improving human, animal, and environmental health through transdisciplinary cooperation. Global policies necessitate going beyond the classical risk assessment for guaranteeing human health through actions and implementation of the One Health approach. In this context, a new perspective is proposed for the integration of microbiome biomarkers and next generation probiotics potentially impacting and modulating not only human health, but plant, animal health, and the environment.

First Report of Crown Gall of Kiwifruit (Actinidia deliciosa) Caused by Agrobacterium fabacearum in China and the Establishment of Loop-Mediated Isothermal Amplification Technique

Kiwifruit is moderately sweet and sour and quite popular among consumers; it has been widely planted in some areas of the world. In 2019, the crown gall disease of kiwifruit was discovered in the main kiwifruit-producing area of Guizhou Province, China. This disease can weaken and eventually cause the death of the tree. The phylogeny, morphological and biological characteristics of the bacteria were described, and were related to diseases. The pathogenicity of this species follows the Koch hypothesis, confirming that A. fabacearum is the pathogen of crown gall disease of kiwifruit in China. In this study, Loop-mediated isothermal amplification (LAMP) analysis for genome-specific gene sequences was developed for the specific detection of A. fabacearum. The detection limit of the LAMP method is 5 × 10^-7 ng/μL, which has high sensitivity. At the same time, the amplified product is stained with SYBR Green I after the reaction is completed, so that the amplification can be detected with the naked eye. LAMP analysis detected the presence of A. fabacearum in the roots and soil samples of the infected kiwifruit plant. The proposed LAMP detection technology in this study offers the advantages of ease of operation, visibility of results, rapidity, accuracy and high sensitivity, making it suitable for the early diagnosis of crown gall disease of kiwifruit.

From Strain Characterization to Field Authorization: Highlights on Bacillus velezensis Strain B25 Beneficial Properties for Plants and Its Activities on Phytopathogenic Fungi

Agriculture is in need of alternative products to conventional phytopharmaceutical treatments from chemical industry. One solution is the use of natural microorganisms with beneficial properties to ensure crop yields and plant health. In the present study, we focused our analyses on a bacterium referred as strain B25 and belonging to the species Bacillus velezensis (synonym B. amyloliquefaciens subsp. plantarum or B. methylotrophicus), a promising plant growth promoting rhizobacterium (PGPR) and an inhibitor of pathogenic fungi inducing crops diseases. B25 strain activities were investigated. Its genes are well preserved, with their majority being common with other Bacillus spp. strains and responsible for the biosynthesis of secondary metabolites known to be involved in biocontrol and plant growth-promoting activities. No antibiotic resistance genes were found in the B25 strain plasmid. In vitro and in planta tests were conducted to confirm these PGPR and biocontrol properties, showing its efficiency against 13 different pathogenic fungi through antibiosis mechanism. B25 strain also showed good capacities to quickly colonize its environment, to solubilize phosphorus and to produce siderophores and little amounts of auxin-type phytohormones (around 13,051 µg/mL after 32 h). All these findings combined to the fact that B25 demonstrated good properties for industrialization of the production and an environmental-friendly profile, led to its commercialization under market authorization since 2018 in several biostimulant preparations and opened its potential use as a biocontrol agent.