Screening, identification, optimization of fermentation conditions, and extraction of secondary metabolites for the biocontrol of Rhizoctonia Solani AG-3

Optimization of the fermentation media and growth conditions of Bacillus velezensis BHZ-29 using a Plackett-Burman design experiment combined with response surface methodology

Introduction

Bacillus velezensis occurs extensively in the soil environment. It produces a range of antimicrobial compounds that play an important role in the field of biological control. However, during the actual application process it is often affected by factors such as the medium formulation and fermentation conditions, and therefore biocontrol measures often do not achieve their expected outcomes.

Methods

In this study, the B. velezensis BHZ-29 strain was used as the research object. The carbon and nitrogen sources, and inorganic salts that affect the number of viable bacteria and antibacterial potency of B. velezensis BHZ-29, were screened by a single factor test. A Plackett-Burman design experiment was conducted to determine the significant factors affecting the number of viable bacteria and antibacterial potency, and a Box-Behnken design experiment was used to obtain the optimal growth of B. velezensis BHZ-29. The medium formula that produced the highest number of viable bacteria and most antibacterial substances was determined. The initial pH, temperature, amount of inoculant, liquid volume, shaking speed, and culture time were determined by a single factor test. The factors that had a significant influence on the number of viable bacteria of B. velezensis BHZ-29 were selected by an orthogonal test. A Box-Behnken design experiment was conducted to obtain the optimal fermentation conditions, and highest number of viable bacteria and antibacterial titer.

Results

Molasses, peptone, and magnesium sulfate had significant effects on the viable count and antibacterial titer of B. velezensis BHZ-29. The viable count of B. velezensis BHZ-29 increased from 7.83 × 109 to 2.17 × 1010 CFU/mL, and the antibacterial titer increased from 111.67 to 153.13 mm/mL when the optimal media were used. The optimal fermentation conditions for B. velezensis BHZ-29 were as follows: temperature 25.57°C, pH 7.23, culture time 95.90 h, rotation speed 160 rpm, amount of inoculant 2%, and liquid volume 100 ml. After the optimization of fermentation conditions, the number of viable bacteria increased to 3.39 × 1010 CFU/mL, and the bacteriostatic titer increased to 158.85 mm/ml.The plant height and leaf number of cotton plants treated with BHZ-29 fermentation broth were higher than those of cotton inoculated with Verticillium dahliae. The number of bacteria was 1.15 × 107 CFU/g, and the number of fungi was 1.60 × 105 spores/g. The disease index of the cotton seedlings treated with the optimized fermentation broth was 2.2, and a control effect of 93.8% was achieved. B. velezensis BHZ-29 could reduce the disease index of cotton Verticillium wilt and had a controlling effect on the disease. The best effect was achieved in the treatment group with an inoculation concentration of 2 × 108 CFU/ml, the disease index was 14.50, and a control effect of 84.18% was achieved.

Discussion

The fermentation process parameters of the number of viable bacteria and antibacterial titer by strain B. velezensis BHZ-29 were optimized to lay a foundation for the practical production and application of strain B. velezensis BHZ-29 in agriculture.

Unraveling the Red Sea soft coral Sarcophyton convolutum potentials against oxidative and inflammatory stresses in zebrafish

The Red Sea is one of the world's hotspots for biodiversity, and for marine natural products (MNPs) as well. These MNPs attract special interest for their capabilities to combat inflammatory and oxidative stress-related diseases, being some of the most serious health problems worldwide nowadays. The current study aimed to identify the bioactive ingredients of the Red Sea soft coral Sarcophyton convolutum, and to assess its protective potentials against oxidative and inflammatory stresses. Coral extract (CE) was analyzed using GC-MS and HPLC. In a protection trial, adult zebrafish were intraperitoneally injected with two doses of crab extract, i.e. 50 and 500 μg/fish in 1 % DMSO as a vehicle, then challenged with 30 μg L-1 of CuSO4 for 48 h. All groups, but the negative control one, were challenged with 30 μg L-1 of CuSO4. Total antioxidant activity, as well as mRNA levels of proinflammatory markers and antioxidant enzyme genes were measured. The results showed richness of S. convolutum extract with various bioactive ingredients, including phenolic compounds, flavonoids, alkanes, fatty acids, sesquiterpenes, and pheromone-like substances. CuSO4 significantly induced the expected signals of inflammatory and oxidative stress, reducing both the antioxidant activity and increasing proinflammatory marker genes. However, CE, especially the low dose, showed significant capability to reduce proinflammatory markers and elevating the total antioxidant activity. Therefore, we concluded that S. convolutum can be a promising source for future efforts of drug discovery and a wide spectrum of pharmaceutical products.

Antibacterial Activity of a New Strain of Streptomyces maritimus MSQ21 against Ralstonia solanacearum

<b>Background and Objective:</b> Actinobacteria represent the most prominent group of microorganisms, which produce a vast number of bioactive compounds especially antibiotics. The present study investigated the antibacterial activity of some actinomycete isolates against <i>Ralstonia solanacearum</i> type 3 biovar 2 (phytopathogenic bacterium that causes tomato wilt disease and brown rot of potatoes). <b>Materials and Methods:</b> The most potent actinomycete isolates in the antibacterial activity was further identified up to species based on its phenotypic and molecular characteristics. Additionally, the most suitable carbon and nitrogen sources for increasing the antibacterial activity were also investigated. <b>Results:</b> Interestingly, <i>Streptomyces </i>isolate MSQ21 achieved the highest antibacterial activity against <i>R. solanacearum</i> with an inhibition zone of 18 mm. 16S rRNA gene analysis suggested that <i>Streptomyces </i>MSQ21 was identified as a strain of <i>S. maritimus</i> Glycerol (2.25%, w/v) and (NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub> (0.13%, w/v) were the most suitable carbon and nitrogen sources for increasing the antibacterial activity. <b>Conclusion:</b> It could be concluded that the maximum antibacterial activity (30mm) produced by <i>S. maritimus </i>strain MSQ21 against <i>R. solanacearum </i>could be obtained by using the modified starch nitrate medium containing (g L<sup>1</sup>): Glycerol, 25: Ammonium sulphate, 1.6: Dipotassium hydrogen phosphate, 1: Magnesium sulphate, 0.5: Sodium chloride, 0.5: Calcium carbonate, 3: Ferrous sulphate and 0.01: Distilled water up to 1 L and under the following conditions: Temperature 30°C, agitation speed 250 rpm, inoculum size 1-50 mL medium, incubation period 4 days and pH 8.5.

Systemic fungicidal activity of phenazine-1-carboxylic acid-valine conjugate against tobacco sore shin and its translocation and accumulation in tobacco (Nicotiana tabacum L.)

BACKGROUND

Tobacco sore shin caused by Rhizoctonia solani Kühn is a major soil-borne fungal disease of tobacco, gradually causing infected stems to become thin and dry, leading to great losses to China's tobacco industry. Fungicides with phloem mobility are needed for application to foliage to effectively control root or vascular system pathogens. In this study, phenazine-1-carboxylic acid-valine conjugate (PCA-Val) with strong phloem mobility was tested for control of tobacco sore shin. In vitro fungicidal activity, systemicity, and in vivo efficacy of PCA-Val against R. solani in tobacco seedling were evaluated.

RESULTS

In vitro fungicidal activity of PCA-L-Val against R. solani was lower than that of PCA or PCA-D-Val, but the in vivo protective activity and curative activity of PCA-L-Val was the highest among these chemicals tested. The systemicity tests in tobacco seedlings revealed that PCA did not possess phloem mobility, while PCA-L-Val and PCA-D-Val exhibited strong phloem mobility and could be transported and accumulated in the lower part of the seedling as well as throughout the phloem. In addition, we also found that, just like reported hormone amino acid conjugates, PCA-L-Val could be hydrolyzed by tobacco seedlings, to release free PCA.

CONCLUSIONS

The current research results indicated that PCA-L-Val possess good phloem transport in tobacco and promising in vivo antifungal activity against R. solani, which can be used as a phloem-mobile fungicide against tobacco sore shin in production practice.

Fungal Endophytes: A Promising Frontier for Discovery of Novel Bioactive Compounds

For years, fungi have served as repositories of bioactive secondary metabolites that form the backbone of many existing drugs. With the global rise in infections associated with antimicrobial resistance, in addition to the growing burden of non-communicable disease, such as cancer, diabetes and cardiovascular ailments, the demand for new drugs that can provide an improved therapeutic outcome has become the utmost priority. The exploration of microbes from understudied and specialized niches is one of the promising ways of discovering promising lead molecules for drug discovery. In recent years, a special class of plant-associated fungi, namely, fungal endophytes, have emerged as an important source of bioactive compounds with unique chemistry and interesting biological activities. The present review focuses on endophytic fungi and their classification, rationale for selection and prioritization of host plants for fungal isolation and examples of strategies that have been adopted to induce the activation of cryptic biosynthetic gene clusters to enhance the biosynthetic potential of fungal endophytes.

Application of response surface methodology for optimization of medium components for the production of secondary metabolites by Streptomyces diastatochromogenes KX852460

A bioactive strain Streptomyces diastatochromogenes KX852460 was selected for the production of secondary metabolites to control the target spot disease on tobacco leaves, caused by the Rhizoctonia solani AG-3. Peanut meal, soluble starch, NaCl, yeast extract, and ammonium sulphate were identified the best ingredient for high antifungal activity of S. diastatochromogenes KX852460 against the R. solani AG-3. For the improved production of secondary metabolites, central composite design of response surface methodology was applied in submerged fermentation. The best concentrations of ingredients were peanut meal 4.88%, soluble starch 4.40%, NaCl 0.52%, yeast extract 0.47%, and ammonium sulphate 0.0360%. Study of metabolism changes in the submerged fermentation process was analyzed. Level of the reducing sugar increased, as the total sugar consumed. Amino nitrogen and total sugar decrease tendency, which indicated the growth of bacteria in submerged fermentation batch. Production of secondary and other metabolites influenced the pH of the fermentation batch.