Antagonistic activity of Bacillus subtilis CW14 and its β-glucanase against Aspergillus ochraceus

Bioactivities evaluation of an endophytic bacterial strain Bacillus tequilensis QNF2 inhibiting apple ring rot caused by Botryosphaeria dothidea on postharvest apple fruits

Apple ring rot, one of the most common apple postharvest diseases during storage, is caused by Botryosphaeria dothidea. Presently, the disease management is primarily dependent on chemical fungicide application. Here we demonstrated an endophyte bacterium Bacillus tequilensis QNF2, isolated from Chinese leek (Allium tuberosum) roots considerably suppressed B. dothidea mycelial growth, with the highest suppression of 73.56 % and 99.5 % in the PDA and PDB medium, respectively in vitro confront experiments. In in vivo experiments, B. tequilensis QNF2 exhibited a control efficacy of 88.52 % and 100 % on ring rot disease on postharvest apple fruits inoculated with B. dothidea disc and dipped into B. dothidea culture, respectively. In addition, B. tequilensis QNF2 volatile organic compounds (VOCs) also manifested markedly inhibition against B. dothidea mycelial growth and the ring rot on postharvest apple fruits. Moreover, B. tequilensis QNF2 severely damaged the mycelial morphology of B. dothidea. Finally, B. tequilensis QNF2 significantly repressed the expression of six pathogenicity-related genes, such as adh, aldh, aldh3, galm, pdc1, pdc2, involved in glycolysis/gluconeogenesis of B. dothidea. The findings of the study proved that B. tequilensis QNF2 was a promising alternative for controlling apple ring rot of postharvest apple fruit.

Antifungal, antiaflatoxigenic, and cytotoxic properties of bioactive secondary metabolites derived from Bacillus species

Aflatoxins (AFs) are hazardous carcinogens and mutagens produced by some molds, particularly Aspergillus spp. Therefore, the purpose of this study was to isolate and identify endophytic bacteria, extract and characterize their bioactive metabolites, and evaluate their antifungal, antiaflatoxigenic, and cytotoxic efficacy against brine shrimp (Artemia salina) and hepatocellular carcinoma (HepG2). Among the 36 bacterial strains isolated, ten bacterial isolates showed high antifungal activity, and thus were identified using biochemical parameters and MALDI-TOF MS. Bioactive metabolites were extracted from two bacterial isolates, and studied for their antifungal activity. The bioactive metabolites (No. 4, and 5) extracted from Bacillus cereus DSM 31T DSM, exhibited strong antifungal capabilities, and generated volatile organic compounds (VOCs) and polyphenols. The major VOCs were butanoic acid, 2-methyl, and 9,12-Octadecadienoic acid (Z,Z) in extracts No. 4, and 5 respectively. Cinnamic acid and 3,4-dihydroxybenzoic acid were the most abundant phenolic acids in extracts No. 4, and 5 respectively. These bioactive metabolites had antifungal efficiency against A. flavus and caused morphological alterations in fungal conidiophores and conidiospores. Data also indicated that both extracts No. 4, and 5 reduced AFB1 production by 99.98%. On assessing the toxicity of bioactive metabolites on A. salina the IC50 recorded 275 and 300 µg/mL, for extracts No. 4, and 5 respectively. Meanwhile, the effect of these extracts on HepG2 revealed that the IC50 of extract No. 5 recorded 79.4 µg/mL, whereas No. 4 showed no cytotoxic activity. It could be concluded that bioactive metabolites derived from Bacillus species showed antifungal and anti-aflatoxigenic activities, indicating their potential use in food safety.

The Prospect of Hydrolytic Enzymes from Bacillus Species in the Biological Control of Pests and Diseases in Forest and Fruit Tree Production

Plant diseases and insect pest damage cause tremendous losses in forestry and fruit tree production. Even though chemical pesticides have been effective in the control of plant diseases and insect pests for several decades, they are increasingly becoming undesirable due to their toxic residues that affect human life, animals, and the environment, as well as the growing challenge of pesticide resistance. In this study, we review the potential of hydrolytic enzymes from Bacillus species such as chitinases, β-1,3-glucanases, proteases, lipases, amylases, and cellulases in the biological control of phytopathogens and insect pests, which could be a more sustainable alternative to chemical pesticides. This study highlights the application potential of the hydrolytic enzymes from different Bacillus sp. as effective biocontrol alternatives against phytopathogens/insect pests through the degradation of cell wall/insect cuticles, which are mainly composed of structural polysaccharides like chitins, β-glucans, glycoproteins, and lipids. This study demonstrates the prospects for applying hydrolytic enzymes from Bacillus sp. as effective biopesticides in forest and fruit tree production, their mode of biocidal activity and dual antimicrobial/insecticidal potential, which indicates a great prospect for the simultaneous biocontrol of pests/diseases. Further research should focus on optimizing the production of hydrolytic enzymes, and the antimicrobial/insecticidal synergism of different Bacillus sp. which could facilitate the simultaneous biocontrol of pests and diseases in forest and fruit tree production.

Isolation and Genome-Based Characterization of Biocontrol Potential of Bacillus siamensis YB-1631 against Wheat Crown Rot Caused by Fusarium pseudograminearum

Fusarium crown rot (FCR) caused by Fusarium pseudograminearum is one of the most serious soil-borne diseases of wheat. Among 58 bacterial isolates from the rhizosphere soil of winter wheat seedlings, strain YB-1631 was found to have the highest in vitro antagonism to F. pseudograminearum growth. LB cell-free culture filtrates inhibited mycelial growth and conidia germination of F. pseudograminearum by 84.14% and 92.23%, respectively. The culture filtrate caused distortion and disruption of the cells. Using a face-to-face plate assay, volatile substances produced by YB-1631 inhibited F. pseudograminearum growth by 68.16%. In the greenhouse, YB-1631 reduced the incidence of FCR on wheat seedlings by 84.02% and increased root and shoot fresh weights by 20.94% and 9.63%, respectively. YB-1631 was identified as Bacillus siamensis based on the gyrB sequence and average nucleotide identity of the complete genome. The complete genome was 4,090,312 bp with 4357 genes and 45.92% GC content. In the genome, genes were identified for root colonization, including those for chemotaxis and biofilm production, genes for plant growth promotion, including those for phytohormones and nutrient assimilation, and genes for biocontrol activity, including those for siderophores, extracellular hydrolase, volatiles, nonribosomal peptides, polyketide antibiotics, and elicitors of induced systemic resistance. In vitro production of siderophore, β-1, 3-glucanase, amylase, protease, cellulase, phosphorus solubilization, and indole acetic acid were detected. Bacillus siamensis YB-1631 appears to have significant potential in promoting wheat growth and controlling wheat FCR caused by F. pseudograminearum.

Isolation, purification, and identification of antifungal protein produced by Bacillus subtilis SL-44 and anti-fungal resistance in apple

Apple anthracnose is a fruit fungal disease that is currently recognized as one of the most severe threats to apples worldwide. In this study, antifungal protein from Bacillus subtilis SL-44 was isolated, purified, identified, and applied for Colletotrichum gloeosporioides control. The antagonistic experiment showed that SL-44 had an excellent broad spectrum against plant pathogenic fungi. The optimal fermentation conditions were as follows: initial pH was 7, inoculum volume was 2%, and rotational speed was 180 r/min. The optimized yield of antifungal protein increased by 45.83% compared with that before. The crude protein was isolated and purified by (NH₄)₂SO₄ precipitation, DEAE-Sepharose Fast Flow, and Sephadex G-100 column chromatography. LC-MS analyzed that antifungal protein was likely to be a novel protein with a molecular weight of 42 kDa. The mechanism revealed that the antifungal protein may disrupt the cell wall structure of C. gloeosporioides and function as its antifungal action. Additionally, antifungal protein significantly alleviated the size of the lesion to more than 70% in the apple infection protection test. In conclusion, antifungal protein has remarkable potential in developing fungicides for the biological control of apple anthracnose. HIGHLIGHTS: 1. B. subtilis SL-44 had broad-spectrum antagonism against plant pathogenic fungi. 2. The optimal fermentation conditions for extracting antifungal protein were optimized. 3. The antifungal protein is a novel protein with a molecular weight of 42 kDa. 4. The mechanism of antifungal protein may disrupt the cell wall structure of C. gloeosporioides.

New Bacillus subtilis Strains Isolated from Prosopis glandulosa Rhizosphere for Suppressing Fusarium Spp. and Enhancing Growth of Gossypium hirsutum L

Rhizobacteria from desert plants can alleviate biotic stress and suppress plant diseases, and consequently can enhance plant growth. Therefore, the current study was performed to isolate and identify Prosopis glandulosa-associating rhizobacteria based on their antagonistic activity against Fusarium species and plant growth-promoting properties. Three bacterial isolates were identified as Bacillus subtilis: LDA-1, LDA-2, and LDA-3. The molecular analysis suggests the biosynthesis of the bacteriocins subtilisin and subtilosin, as well as the lipopeptide iturin, by these strains. In addition, the antagonistic study by dual-culture assay showed a high efficacy of all B. subtilis strains against phytopathogenic fungi (Fusarium nygamai, F. equisseti, F. solani, F. solani ICADL1, and F. oxysporum ICADL2) with inhibition percentages ranging from 43.3 to 83.5% in comparison to the control. Moreover, atomic force microscopy (AFM) analysis showed significant differences in the cell wall topography of the F. solani ICADL1 among the treated mycelia and untreated control. As a result, these three B. subtilis strains were used as bioinoculants for cotton seedlings infected by F. solani ICADL1 in pot trials, and the results revealed that the bacterial inoculations as an individual or combined with F. solani ICADL1 significantly improved cotton root and stem length, lateral roots, indole acetic acid (IAA), and gibberellic acid (GA₃) contents, as well as increased antioxidants, flavonoids, and phenols in comparison to those obtained from healthy and infected control plants. In conclusion, the three bacterial strains of B. subtilis (i.e., LDA-1, LDA-2, and LDA-3) are considered promising tools as biocontrol agents for F. solani and cotton growth promoters, and consequently can be used as bio-ertilizer in sustainable agriculture systems.

Antagonistic Activity and Mechanism of Bacillus subtilis XZ16-1 Suppression of Wheat Powdery Mildew and Growth Promotion of Wheat

Wheat powdery mildew caused by Blumeria graminis f. sp. tritici (Bgt) is one of the most serious wheat diseases in the world. Biological control is considered an environmentally safe approach to control plant diseases. Here, to develop effective biocontrol agents for controlling wheat powdery mildew, antagonistic strain XZ16-1 was isolated and identified as Bacillus subtilis based on the morphological, biochemical, and physiological characteristics and 16S rDNA sequence. The culture filtrate of B. subtilis XZ16-1 and its extracts had a significant inhibitory effect on the spore germination of Bgt. Moreover, the therapeutic and prevention efficacy of the 100% culture filtrate on wheat powdery mildew reached 81.18 and 83.72%, respectively, which was better than that of chemical fungicide triadimefon. Further antimicrobial mechanism analysis showed that the XZ16-1 culture filtrate could inhibit the development of powdery mildew spores by disrupting the cell membrane integrity, causing reductions in the mitochondrial membrane potential, and inducing the accumulation of reactive oxygen species in the spores. Biochemical detection indicated that XZ16-1 could solubilize phosphate, fix nitrogen, and produce hydrolases, lipopeptides, siderophores, and indole-3-acetic acid. Defense-related enzymes activated in wheat seedlings treated with the culture filtrate indicated that disease resistance was induced in wheat to resist pathogens. Furthermore, a 10⁶ CFU/ml suspension of XZ16-1 increased the height, root length, fresh weight, and dry weight of wheat seedlings by 77.13, 63.46, 76.73, and 19.16%, respectively, and showed good growth-promotion properties. This study investigates the antagonistic activity and reveals the action mechanism of XZ16-1, which can provide an effective microbial agent for controlling wheat powdery mildew.

Antifungal properties of rhizobacterial strains in relation to fungi of agricultural crops

On earth, pathogenic fungal infections are considered one of the most common crop problems, accounting for more than 80% of all plant diseases. The production of biologics and the fight against pathogens are highly relevant priorities. In this article, rhizosphere cultures isolated from wheat root tubers have been studied in detail for the development of pathogenic fungi. In the course of research, the inhibitory properties of rhizobacteria against common pathogenic fungi were studied. The main mechanism of antagonism is that bacteria directly affect phytopathogens or increase plant resistance to diseases by enhancing immunity. The antagonistic activity of rhizospheric microorganisms was studied and the level of their action was determined. It has been established that wheat rhizospheric bacteria Escherichia hermannii, Enterobacter cloacae and Rahnella aquatilis affect the development of pathogens that cause Alternaria and Fusarium wilt. In the experiments, 46 strains of rhizobacteria of the genus Enterobacter (strain E. cloacae CCIM1022), Rahnella (R. aquatilis CCIM1023), Pantoea, Pseudomonas, Bacillus, Escherichia were isolated and the effectiveness of their antifungal properties on the reproduction of pathogenic fungi was tested. Pathogenic fungi Alternaria, Fusarium, causing diseases of vegetable and melon crops, were isolated from host plants. It is noted that rhizobacteria have a negative impact and block the development of pure cultures of fungi isolated from tomatoes, zucchini, figs, melons, causing fungal diseases on cups. The 46 isolated and tested strains of rhizobacteria effectively inhibited the development of pathogenic fungi. Of these, Rahnella is the first bacterium studied for this purpose, and has been given great importance in experiments to block the development of Alternaria (A. alternata CCIM 1021). The causative agents of alternariosis are widely open. However, large-scale analysis of their presence and control of pathogens has always been difficult. In experiments to combat the pathogen in the laboratory, a new agent was used to spread nitrogen-fixing bacteria.