TL;DR
Genome mining revealed eight biosynthetic gene clusters associated with antimicrobial secondary metabolites, supporting the genomic characterization of strain BS01 and identifying its biosynthetic potential and identifying its biosynthetic potential.
BACKGROUND Twig blight disease caused by Pestalotiopsis versicolor threatens bayberry (Myrica rubra) cultivation in China, prompting extensive reliance on chemical fungicides with limited long-term efficacy. This study investigated the potential of endophytic bacteria isolated from bayberry leaves as sustainable biocontrol agents against this pathogenic fungus. RESULTS An endophytic bacterium designated strain Bay9 was isolated from healthy bayberry leaves and identified as a Bacillus sp. closely related to Bacillus velezensis based on 16 S rRNA gene sequence analysis. Bay9 exhibited strong antifungal activity against P. versicolor in vitro and showed disease-suppressive effects under semi-controlled greenhouse conditions. On potato dextrose agar (PDA) and in potato dextrose broth (PDB), inhibition rates reached 74.44% and 87.65%, respectively, accompanied by severe ultrastructural damage to fungal hyphae observed by electron microscopy. Cell-free supernatants (CFSs) of Bay9 exhibited concentration-dependent antifungal activity, with inhibition rates of 15.77%, 34.99%, 66.74%, and 98.82% at concentrations of 2.5%, 5%, 10%, and 20% (v/v), respectively. CFSs at EC50 and EC90 concentrations (7.30% and 17.43%, respectively) significantly reduced spore production and germination, induced leakage of intracellular nucleic acids and proteins consistent with membrane perturbation and leakage, but not direct evidence of a defined molecular mechanism and substantially reduced colony formation. In detached leaf assays, EC50 and EC90 treatments reduced lesion development by 65.31% and 94.58%, respectively. Under semi-controlled greenhouse conditions, Bay9 treatment significantly reduced disease incidence (from 97% to 49.33%) and disease severity index (from 82.19% to 38.69%) compared with pathogen-inoculated plants (p < 0.05), without causing phytotoxic effects on bayberry saplings. CONCLUSIONS Bay9 exhibited strong antifungal activity associated with multiple putative mechanisms, potentially involving siderophore production, hydrolytic enzyme activities (protease, amylase, and lipase), and lipopeptide-related metabolites, as suggested by biochemical assays and MALDI-TOF-MS-based tentative identification of surfactin-, iturin-, and fengycin-like compounds. Collectively, these findings suggest that Bay9 has potential as a biocontrol agent against P. versicolor under laboratory, detached-leaf, and semi-controlled greenhouse conditions. However, further studies are required to elucidate the underlying molecular mechanisms and to validate its efficacy under field conditions before practical application can be recommended.
India contributes 26% of global banana production, yet cultivation is severely threatened by Fusarium wilt (Fusarium oxysporum f. sp. cubense, Foc), necessitating sustainable, eco-friendly management strategies. This study evaluated the biocontrol potential of endophytic bacteria isolated from Foc-resistant and -susceptible banana cultivars. Isolates from the pseudostem, corm, and root of the resistant cultivar showed significantly greater inhibitory activity than those from the susceptible cultivar, underscoring the role of host genotype in shaping functionally competent endophytic communities. Among all isolates, Bacillus sp. from the corm of cv. Rose (AB) showed the highest mycelial inhibition of Foc (70.37–76.54%) in vitro. GC-MS-based metabolite profiling revealed a chemically diverse array of secondary metabolites, fatty acid esters, steroids, terpenoids, siloxanes, and nitrogenous compounds. Corm-associated endophytes exhibited membrane-disruptive and cytotoxic activity, while root-associated endophytes contributed protective, defense-modulatory effects. Halomonas sp. RoRo2 and B. subtilis RoC1 showed the highest inhibition in both agar-well and in planta assays, with unsaturated fatty acids and organic acid derivatives implicated as key antifungal effectors acting through multiple biochemical pathways. These findings identify metabolically versatile endophytes as promising candidates for developing efficient, environmentally compatible bioinoculants as sustainable alternatives to chemical control of Fusarium wilt in banana.
Cowpea (Vigna unguiculata subsp. sesquipedalis, also known as yardlong bean) is an important winter horticultural crop in Hainan, and Fusarium wilt seriously threatens its yield and quality. To clarify the pathogen and screen antagonistic bacteria, surveys were conducted in 14 fields across Hainan’s major cowpea-growing areas. The causal agent was isolated, tested for pathogenicity, and identified using morphological and multigene molecular methods. Meanwhile, rhizosphere and endophytic bacteria from healthy plants were screened by dual culture, and candidate strains were phylogenetically analyzed using whole-genome sequencing (285 orthologous single-copy genes). Fusarium wilt occurred in all 14 fields (mean incidence 15.35%, range 3.20–76.40%). Of 44 fungal isolates, six were highly pathogenic and identified as Fusarium oxysporum. Twenty-two bacterial strains showed stable antagonism against F. oxysporum, with inhibition rates ranging from 42.62% to 68.47%. Phylogenetic analysis based on whole-genome sequences identified 15 Bacillus strains to the species level (12 B. velezensis, 2 B. subtilis, 1 B. tropicus), while the remaining seven strains belonged to Lysinibacillus (1), Pantoea (1), Klebsiella (1), Serratia (2), and Pseudomonas (2). Draft genome sequences of all 22 strains were obtained. This study provides a collection of biocontrol bacterial resources and genomic information for managing cowpea Fusarium wilt.
Introduction Fusarium wilt of banana (FWB), caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), poses a serious threat to the safety and sustainable development of the banana industry. Biological control represents one of the most environmentally friendly approaches for managing this disease. Methods In this study, Streptomyces violaceusniger WZS5–6 antifungal activity against Foc TR4 has been investigated through an integrated approach combining antifungal assays, genome analysis, and metabolomic profiling. For the purpose, the effects of the bacterial strain and its cell-free extract on morphological and ultrastructural changes on pathogenic fungal hyphae and spores were assessed using scanning and transmission electron microscopy. LC–MS analysis was used to identify the metabolites responsible for antifungal activity. We further explored the potential of S. violaceusniger WZS5–6 against Foc TR4 through in planta validation. Results Streptomyces violaceusniger WZS5–6 exhibited a strong inhibition rate of 91.57% on Foc TR4. The cell-free extract obtained from S. violaceusniger WZS5–6 strongly inhibited Foc TR4 with an EC50 value of 91.62 µg·mL-1, indicating the presence of antifungal bioactive metabolites. The results showed that S. violaceusniger WZS5–6 significantly inhibited the mycelial growth of Foc TR4 and induced alterations in spore morphology, mycelial ultrastructure, and cell membrane leakage. Metabolomic profiling of the S. violaceusniger WZS5–6 extracts revealed numerous antifungal metabolites, among which the key metabolites, viz., citronellic acid and furanodienone, exhibited strong inhibitory effects on Foc TR4, with antifungal activity of 61.13% and 57.44%, respectively. Moreover, strain WZS5–6 not only demonstrated 61.54% control efficacy against FWB in a pot experiment but also showed promising growth-promoting effects on banana plants. Discussion This study demonstrates that S. violaceusniger WZS5–6 inhibits Foc TR4 through a multi-level mechanism involving cellular disruption, metabolic adaptation, and activation of host defense responses. These findings highlight the potential of S. violaceusniger WZS5–6 as a promising novel candidate strain to be employed as a biological control agent of FWB.
Fusarium oxysporum f. sp. cubense (Foc) is a soil-borne fungal pathogen responsible for fusarium wilt, which constitutes one of the major constraints in banana cultivation. Information on the occurrence and molecular characteristics of Foc in Malang Regency, one of the banana-producing areas in East Java, Indonesia, remains limited, hindering effective disease surveillance and management. This study was conducted to isolate and characterize fungal isolates associated with fusarium wilt disease in banana plants using an integrated approach combining morphological characterization, pathogenicity testing, PCR amplification, ITS sequence analysis, and phylogenetic analysis. Three fungal isolates were recovered from symptomatic banana plants collected in Donomulyo, Malang Regency, and one representative isolate (DNM) was selected for molecular characterization based on its morphological similarity to the other isolates. Morphological observations revealed characteristics typical of Fusarium oxysporum. ITS sequence analysis showed 100% query coverage and 100% sequence identity with reference Foc sequences available in GenBank, while phylogenetic analysis clustered the DNM isolate with reference Foc isolates with 94% bootstrap support. Pathogenicity assays demonstrated that the isolate induced typical fusarium wilt symptoms, resulting in an LDI of 16.39% at 14 DAI and an RDI of 41.67% at 45 DAI. These findings provide baseline information on putative Foc isolates in Malang Regency, particularly in the Donomulyo area, and establish an integrated characterization framework to support disease surveillance, early detection, and the development of integrated management strategies for fusarium wilt in banana production systems.
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