Antifungal mechanism of Streptomyces ma. FS-4 on fusarium wilt of banana

Siderophore of plant growth promoting rhizobacterium origin reduces reactive oxygen species mediated injury in Solanum spp. caused by fungal pathogens

AIMS

The study aims to explore antifungal properties of bacillibactin siderophore produced by the plant growth-promoting rhizobacterium (PGPR) Bacillus subtilis against fungal phytopathogens Alternaria porri and Fusarium equiseti isolated from Solanum lycopersicum and Solanum melongena plants.

METHODS AND RESULTS

Alternaria porri and F. equiseti were isolated from infected plants of eggplant and tomato, respectively. A plate assay was employed to assess the effect of bacillibactin against the phytopathogens. The antifungal potential of the PGPR was evaluated by estimation of dry fungal biomass, visualization of cellular deformity using compound and scanning electron microscopy, antioxidative enzyme assay and analysis of membrane damage via using lipid peroxidation. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis was employed to investigate changes in intracellular iron content. The impact of bacillibactin on pathogenesis was evaluated by infecting detached leaves of S. lycopersicum and S. melongena plants with both the pathogens and treating the infected leaves with bacillibactin. Leaves were further investigated for ROS accumulation, extent of necrosis and cell death. Our findings revealed significant damage to the hyphal structure of A. porri and F. equiseti following treatment with bacillibactin. Biomass reduction, elevated antioxidative enzyme levels, and membrane damage further substantiated the inhibitory effects of the siderophore on fungal growth. ICP-AES analysis indicates an increase in intracellular iron content suggesting enhanced iron uptake facilitated by bacillibactin. Moreover, application of 1500 µg ml-1 bacillibactin on infected leaves demonstrated a substantial inhibition of ROS accumulation, necrosis, and cell death upon bacillibactin treatment.

CONCLUSIONS

This study confirms the potent antagonistic activity of bacillibactin against both the phytopathogens A. porri and F. equiseti growth, supporting its potential as a promising biological control agent for fungal plant diseases. Bacillibactin-induced morphological, physiological, and biochemical alterations in the isolated fungi and pathogen-infected leaves highlight the prospects of bacillibactin as an effective and sustainable solution to mitigate economic losses associated with fungal infections in vegetable crops.

Utilization of palm oil mill effluent as a novel substrate for the production of antifungal compounds by Streptomyces philanthi RM-1-138 and evaluation of its efficacy in suppression of three strains of oil palm pathogen

AIMS

This study aimed to use palm oil mill effluent (POME) as a renewable resource for the production of antifungal compounds by Streptomyces philanthi RM-1-138 against Ganoderma boninense, Ceratocystis paradoxa and Curvularia oryzae.

METHODS AND RESULTS

The efficacy of antifungal compounds RM-1-138 against the three strains of fungal oil palm pathogen was evaluated both in vitro and on oil palm leaf segments. In vitro studies using confrontation tests on glucose yeast-malt extract (GYM) agar plates indicated that the strain RM-1-138 inhibited the growth of all three fungal pathogenic strains. The antifungal compounds produced in the GYM medium exhibited significantly higher inhibition (79%-100%) against the three fungal pathogens than using the diluted POME (50%) medium (80%-83% inhibition). The optimum condition for the production of antifungal compounds from the strain RM-1-138 was as following: POME of 47,966 mg L^-1 chemical oxygen demand (COD), the initial pH at 7.0 and supplemented with yeast extract (0.4%). Meanwhile, severe morphological and internal abnormalities in C. oryzae hyphae were observed under a scanning electron microscope and transmission electron microscope. In vivo experiment on oil palm leaf segments indicated that the efficacy of the antifungal compounds RM-1-138 (DSI = 1.3) were not significantly difference in the suppression of Curvularia leaf spot compared with the two commercial chemical fungicides of mancozeb^® (DSI = 1.0) and tetraconazole^® (DSI = 1.3).

CONCLUSIONS

Antifungal compounds produced by S. philanthi RM-1-138 grown in POME have the potential to inhibit fungal pathogens.

SIGNIFICANCE AND IMPACT OF THE STUDY

The POME (about 47 mg L^-1 COD) with the initial pH of 7.0 and supplementation of 0.4% nitrogen could be used as a culture medium for the growth and production of antifungal compounds of S. philanthi RL-1-138. In addition, the antifungal compound RM-1-138 could suppress the three strains of oil palm fungal pathogen tested on oil palm leaf segment.

Anti-Foc RT4 Activity of a Newly Isolated Streptomyces sp. 5-10 From a Medicinal Plant (Curculigo capitulata)

Fusarium wilt of banana caused by Fusarium oxysporum f. sp. cubense (Foc) is a disastrous soil-borne fungal disease. Foc tropical race 4 (Foc TR4) can infect almost all banana cultivars. Until now, there is a shortage of safety and effective control methods and commercial banana cultivars with a resistance against Foc TR4. Biocontrol using environmentally friendly microbes is a promising strategy for the management of Foc TR4. Here, a strain 5-10, newly isolated from a medicinal plant (Curculigo capitulata), exhibited a high antifungal activity against Foc TR4. Combing the morphological characteristics and molecular identification, strain 5-10 was classified as a Streptomyces genus. The sequenced genome revealed that more than 39 gene clusters were involved in the biosynthesis of secondary metabolites. Some multidrug resistance gene clusters were also identified such as mdtD, vatB, and vgaE. To improve the anti-Foc TR4 activity of the strain 5-10 extracts, an optimization method of fermentation broth was established. Antifungal activity increased by 72.13% under the fermentation system containing 2.86 g/L of NaCl and 11.57% of inoculation amount. After being treated with the strain 5-10 extracts, the Foc TR4 hyphae shrinked, deformed, and ruptured. The membrane integrity and cell ultrastructure incurred irreversible damage. Streptomyces sp. 5-10 extracts play a fungicidal role in Foc TR4. Hence, Streptomyces sp. 5-10 will be a potential biocontrol agent to manage fungal diseases by exploring the microbial fertilizer.