Biocontrol Potential of Bacillus stercoris Strain DXQ-1 Against Rice Blast Fungus Guy11

Abstract

Fungal diseases severely threaten global agriculture, while conventional chemical fungicides face increasing restrictions due to environmental and safety concerns. In this study, we isolated a soil-derived Bacillus stercoris strain, DXQ-1, exhibiting strong antagonistic activity against plant pathogenic fungi, notably Magnaporthe oryzae, the causal agent of rice blast. Scanning electron microscopy revealed that DXQ-1 disrupts fungal hyphae and inhibits conidial germination, with a 24 h crude broth treatment reducing germination to 83.33% and completely blocking appressoria formation. LC-MS-based metabolomic analysis identified key antifungal components, including lipids (35.83%), organic acid derivatives (22.15%), and small bioactive molecules (e.g., Leu-Pro, LPE 15:0). After optimizing fermentation conditions (LB medium, pH 7.0, 28 °C, 48 h), the broth showed >90% inhibition against M. oryzae and Nigrospora oryzae and retained high thermal (68 °C, 1 h) and UV (4 h) stability. Field trials demonstrated effective disease control and significant promotion of rice growth, increasing plant height (17.7%), fresh weight (53.3%), and dry weight (33.3%). These findings highlight DXQ-1 as a promising biocontrol agent, offering a sustainable and effective alternative for managing fungal diseases in crops.

Keywords: Bacillus; Magnaporthe oryzae; antifungal metabolites; fungal pathogen; plant disease control.

Figure 1

Identification and characteristics of B. stercoris strain DXQ-1. (A) The colony morphology, ultrastructure under the electron microscope, and bacterial staining of the of B. stercoris strain DXQ-1. (B) A phylogenetic tree was constructed based on the complete 16S rRNA gene sequences of strain DXQ-1 and other strains retrieved from GenBank. The tree was constructed using the neighbor-joining (NJ) algorithm, and 1000 bootstrap replicates were performed using MEGA 7.0 software. The bootstrap value (%) is indicated proximal to the nodes.

Figure 2

Antagonistic activity of the biocontrol bacterium B. stercoris strain DXQ-1 against the M. oryzae strain Guy11. (A) The mycelial morphology of M. oryzae strain Guy11. Scale bar = 1 cm. (B) DXQ-1 was inoculated into Guy11 colonies, and the colonies were photographed. (C) The ultrastructure of Guy11 in the control group; scale bar = 5 µm. (D) The ultrastructure of Guy11 after co-cultivation with B. stercoris strain DXQ-1; scale bar = 5 µm.

Figure 3

Effect of DXQ-1 extracts on disease incidence caused by M. oryzae. (A,B) Lesion symptoms and length after being incubated with Guy11, which included mixed fermentation broth and then M. oryzae spores 24 h later in the greenhouse. Rice leaves were incubated with 0 (CK), 1, 10, or 100% DXQ-1 fermentation broth. (C) Effect of DXQ-1 fermentation broth on spore germination of M. oryzae. Scale bar: 20 μm. (D,E) Lesion symptoms and blast disease lesion density after the therapeutic treatment, which involved spraying rice blast spores, followed by the fermentation broth 24 h later. Rice leaves were sprayed with DXQ-1 fermentation broth. Blast disease lesion density was quantified in infected leaf segments (5 cm in length) 5 days post-infection. The values are the means ± SDs. Asterisks denote a significant difference from the CK, determined using Student’s t-test (* indicates p < 0.05). n = 30 independent leaves in (B,E).

Figure 4

Active antimicrobial substance analysis of strain DXQ-1. (A) The mycelial morphology of Guy11 cultured on CM containing DXQ-1 extracts, petroleum extracts, dichloromethane extracts, n-butanol extracts, ethyl acetate extracts, and water extracts. PET: petroleum ether; EAC: acetic ester; DCM: dichloromethane; NBA: n-butanol. (B) Detection of the molecular weight of antibacterial substances using semipermeable membranes.

Figure 5

Antimicrobial spectrum of DXQ-1 extracts against phytopathogenic fungi. The mycelial morphology and colony diameters of Rhizoctonia solani, Fusarium graminearum, Nigrospora oryzae, Magnaporthe oryzae, and Bipolaris maydis were assessed on PDA plates supplemented with DXQ-1 extracts. The extracts were obtained from DXQ-1 cultured in PDB medium and incorporated into the plates. Plates without DXQ-1 extract served as controls (CK). Scale bar = 1 cm.

Figure 6

Plant-growth-promoting effects of DXQ-1. (A) Colony morphology of DXQ-1 cultured on PVK, calcium phytate, Ashby, and CAS media, indicating its abilities in phosphorus solubilization (PVK), organic phosphorus solubilization (calcium phytate), nitrogen fixation (Ashby), and siderophore production (CAS). (B) Phenotype, (C) plant height, (D) fresh weight, and (E) dry weight of TP309 rice plants after inoculation with DXQ-1 fermentation broth; sterile PDB served as the control. Data are presented as mean ± SD. Asterisks indicate statistically significant differences compared to the control (Student’s t-test, * p < 0.05). Scale bar in (A) = 1 cm.