Purification and identification of a novel antifungal protein from Bacillus subtilis XB-1

Medium Optimization and Fermentation Kinetics for Antifungal Compounds Production by an Endophytic Paenibacillus polymyxa DS-R5 Isolated from Salvia miltiorrhiza

An endophytic bacterium Paenibacillus polymyxa DS-R5 which can effectively inhibit the growth of pathogenic fungi was isolated from Salvia miltiorrhiza in our previous study. By using hydrochloric acid precipitation, methanol extraction, silica gel column isolation, dextran gel chromatography column, and HPLC, 3 compounds with antifungal activity were isolated. To further improve the production of antifungal compounds produced by this strain, fermentation medium was optimized using one-factor-at-a-time, Plackett-Burman design, and Box-Behnken design experiments. Through statistical optimization, the optimal medium composition was determined to be as follows: 14.7 g/l sucrose, 20.0 g/l soluble starch, 7.0 g/l corn steep liquor, 10.0 g/l (NH4)2SO4, and 0.7 g/l KH2PO4. In this optimized medium, the highest titer of antifungal compounds reached 3452 U/ml, which was 123% higher than that in the initial medium. In addition, in order to guide scale-up for production, logistic and Luedeking-Piret equations were proposed to predict the cell growth and antifungal compounds production. The fermentation kinetics and empirical equations of the coefficients (X0, Xm, μm, α, and β) for the two models were reported, which will aid the design and optimization of industrial processes. The degrees of fit between calculated values of the model and the experimental data were 0.989 and 0.973, respectively. The results show that the cell growth and product synthesis models established in this study may better reflect the dynamic process of antifungal compounds production and provide a theoretical basis for further optimization and on-line monitoring of the fermentation process.

Genome and Transcriptome Analysis to Elucidate the Biocontrol Mechanism of Bacillus amyloliquefaciens XJ5 against Alternaria solani

Early blight, caused by Alternaria solani, is an important disease affecting tomatoes. Biological control offers an environmentally friendly approach to controlling pathogens. Herein, we identified a B. amyloliquefaciens strain XJ5 and investigated its biocontrol mechanism against A. solani. A. solani growth was significantly inhibited by XJ5, with the inhibition rate of cell-free culture supernatants reaching 82.3%. Furthermore, XJ5 crude protein extracts inhibited conidia germination and altered the mycelial morphology of A. solani. To uncover the potential biocontrol mechanism of XJ5, we analyzed its genome sequence and transcriptome. The genome of XJ5 comprised a 4.16 Mb circular chromosome and two circular plasmids. A total of 13 biosynthetic gene clusters and 127 genes encoding hydrolases were identified, suggestive of the ability of XJ5 to secrete antagonistic secondary metabolites and hydrolases. Transcript analysis revealed 174 differentially expressed genes on exposing A. solani to XJ5 crude protein extracts. The expression of genes related to chitin and mannose synthesis was downregulated, indicating that XJ5 metabolites may impact chitin and mannose synthesis in A. solani. Overall, these findings enhance our understanding of the interactions between B. amyloliquefaciens and phytopathogens and pave the way for the agricultural application of this promising biocontrol agent.

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.

GroEL protein from the potential biocontrol agent Rhodopseudomonas palustris enhances resistance to rice blast disease

BACKGROUND

GroEL, which is a chaperone, plays a key role in maintaining protein homeostasis and, among other functions, serves to prevent protein misfolding and aggregation. In addition, the GroEL protein also has a significant effect on enhancing plant resistance and inhibiting plant diseases. However, the function of the GroEL protein in the inhibition of rice blast remains unknown.

RESULTS

Field experiment results show that photosynthetic bacteria PSB-06 have a good control effect on Magnaporthe oryzae. PSB-06 also can promote rice growth and enhance stress resistance. A GroEL protein which was separated and purified from photosynthetic bacteria had a significant antagonistic effect on appressorial formation and pathogenicity of Magnaporthe oryzae, meanwhile transcriptional analysis demonstrated that the GroEL protein could improve the expression of defense gene of rice.

CONCLUSION

Our results show that the photosynthetic bacteria Rhodopseudomonas palustris significantly controls rice blast disease. Its action involves an extracellular GroEL protein, which inhibits appressoria formation, antagonizes the pathogenicity of Magnaporthe oryzae and promotes a host defense response. The research results provide evidence of the potential of this photosynthetic bacterium as a biocontrol agent at least for rice blast control. © 2021 Society of Chemical Industry.

Isolation and Characterization of Beneficial Bacteria from Food Process Wastes

Significant quantities of food waste are accumulated globally on an annual basis, with approximately one-third of the food produced (equivalent to 1.3 billion tons of food) being wasted each year. A potential food waste recycling application is its utilization as a soil conditioner or fertilizer, whereby it increases the soil organic content and microbial biomass. This study evaluated the effectiveness of food waste as a microbial resource by analyzing the microbial community composition and isolating plant growth-promoting bacteria (PGPB) in food waste obtained from various sources. High-throughput sequencing identified 393 bacterial operational taxonomic units in the food process waste (FPW) samples. Moreover, the results showed that Firmicutes was abundant in the waste samples, followed by Bacteroidetes and Proteobacteria. A total of 92 bacteria were isolated from FPW. Moreover, the cultivable strains isolated from FPW belonged to the genus Bacillus, followed by Streptomyces and Proteus. Six isolated bacteria exhibited beneficial traits, including indole acetic acid production, antifungal resistance and extracellular lysis. FPW is a valuable microbial resource for isolation of PGPB, and its use as a fertilizer may enable a reduction in chemical fertilizer usage, thereby mitigating the corresponding adverse environmental impacts on sustainable crop development.

An Antifungal Chitosanase from Bacillus subtilis SH21

Bacillus subtilis SH21 was observed to produce an antifungal protein that inhibited the growth of F. solani. To purify this protein, ammonium sulfate precipitation, gel filtration chromatography, and ion-exchange chromatography were used. The purity of the purified product was 91.33% according to high-performance liquid chromatography results. Sodium dodecyl sulfate–polyacrylamide gel electrophoresis and liquid chromatography–tandem mass spectrometry (LC–MS/MS) analysis revealed that the molecular weight of the protein is 30.72 kDa. The results of the LC–MS/MS analysis and a subsequent sequence-database search indicated that this protein was a chitosanase, and thus, we named it chitosanase SH21. Scanning and transmission electron microscopy revealed that chitosanase SH21 appeared to inhibit the growth of F. solani by causing hyphal ablation, distortion, or abnormalities, and cell-wall depression. The minimum inhibitory concentration of chitosanase SH21 against F. solani was 68 µg/mL. Subsequently, the corresponding gene was cloned and sequenced, and sequence analysis indicated an open reading frame of 831 bp. The predicted secondary structure indicated that chitosanase SH21 has a typical a-helix from the glycoside hydrolase (GH) 46 family. The tertiary structure shared 40% similarity with that of Streptomyces sp. N174. This study provides a theoretical basis for a topical cream against fungal infections in agriculture and a selection marker on fungi.

Secondary metabolites from Bacillus sp. MERNA97 extract attenuates the oxidative stress, genotoxicity and cytotoxicity of aflatoxin B1 in rats

This study aimed to determine the bioactive compounds of Bacillus sp. MERNA97 extract and to evaluate their efficacy against the oxidative damage, genotoxicity, chromosomal aberration and DNA fragmentation in rats treated with AFB1. Sixty male Sprague-Dawley rats were divided into 6 groups and treated for 6 weeks and included the control group, AFB1-treated group (80 μg/kg b. w), the groups treated with Bacillus extract (BE) at low (2 mg/kg b.w) or high (4 mg/kg b.w) dose and the groups treated with AFB1 plus BE at the two doses. Blood and tissues samples were collected for different assays. The GC-MS results revealed the isolation of 44 compounds belong to different classes. The in vivo results showed that AFB1 disturbs all the biochemical parameters, oxidative stress markers, cytokines gene expression chromosomal aberration and DNA fragmentation along with the histological changes in the liver tissue. BE at the two tested doses induced a significant improvement in all parameters tested and the histological picture in a dose dependent manner. It could be concluded that the extract of Bacillus sp. MERNA97 isolated from the marine environment in the Red Sea is a promise as a source of novel compounds with therapeutically benefits.

Antifungal Mechanism of Dipicolinic Acid and Its Efficacy for the Biocontrol of Pear Valsa Canker

Valsa pyri is a fatal canker pathogen that causes significant reduction of crop yield in pear orchards. V. pyri invades the trunk phloem, and is difficult to control by chemical treatment. In this work, it was found for the first time that Bacillus subtilis-produced dipicolinic acid (DPA) exhibits antifungal activity against different canker pathogens, including Alteraria alternata, Botryosphaeria dothidea, Rhizoctonia solani, and V. pyri. Growth inhibition of V. pyri was observed at less than 5 mM concentration (pH = 5.6). DPA showed the highest antifungal activity at acidic pH values and in the presence of bivalent metals, such as zinc(II), cobalt(II), and copper(II). Measurement of mRNA expression levels and scanning electron microscope (SEM) observations revealed that DPA causes V. pyri apoptosis via inhibition of chitin biosynthesis and subsequent cell lysis. Interestingly, DPA showed high stability in the pear bark and was able to cross the pear tree bark into the phloem, protecting the internal phases of the pear trunk. In preventive applications, DPA reduced the canker symptoms of V. pyri on Cuigan pear trees by 90%. Taken together, an efficient strategy for the management of V. pyri-caused canker disease was developed using a novel antifungal agent, DPA, with strong antifungal activity and particular diffusion properties.