Monitoring Tritrophic Biocontrol Interactions Between Bacillus spp., Fusarium oxysporum f. sp. cubense, Tropical Race 4, and Banana Plants in vivo Based on Fluorescent Transformation System

Optimizing surfactin yield in Bacillus velezensis BN to enhance biocontrol efficacy and rhizosphere colonization

Introduction

Surfactins, a class of lipopeptide biosurfactants secreted by plant growth-promoting rhizobacteria (PGPR), have garnered significant attention due to their dual functionality in promoting plant growth and controlling plant diseases. Their potential as biopesticides is underscored by their unique physicochemical properties and biological activities. However, the practical application of surfactin is currently limited by its low yield in natural strains.

Methods

This study aimed to optimize the culture conditions for Bacillus velezensis BN, a strain with exceptional biocontrol properties, to enhance its surfactin yield. Critical factors, including nitrogen sources and amino acid supplementation, were systematically investigated to determine their impact on surfactin production.

Results

The study revealed that nitrogen sources and amino acid supplementation were pivotal factors influencing surfactin yield. Compared to the baseline, these factors resulted in a remarkable 5.94-fold increase in surfactin production. Furthermore, a positive correlation was established between surfactin yield and biocontrol efficacy. Enhanced surfactin yield was associated with improved antifungal activity, biofilm formation, and rhizosphere colonization capacity of B. velezensis BN on potato plantlets.

Discussion

These findings provide novel insights into the practical application of surfactin and establish a scientific foundation for the development of innovative and eco-friendly antifungal agents suitable for agricultural use. The results demonstrate that optimizing culture conditions can significantly enhance surfactin yield and biocontrol efficacy, thereby highlighting the potential for sustainable agricultural practices.

The fall armyworm converts maize endophytes into its own probiotics to detoxify benzoxazinoids and promote caterpillar growth

BACKGROUND

The fall armyworm (FAW, Spodoptera frugiperda) threatens maize production worldwide, and benzoxazinoids (Bxs) are known as the main secondary metabolites produced by maize to defend against FAW. However, we do not yet know whether and in what ways certain endophytes in the digestive system of FAW can metabolize Bxs, thus enhancing the fitness of FAW when feeding on maize.

RESULTS

Using Bxs as the sole carbon and nitrogen source, we isolated Pantoea dispersa from the guts of FAW. P. dispersa can colonize maize roots and leaves as indicated by GFP-labeling and further successfully established itself as an endophyte in the Malpighian tubules and the gut of FAW after FAW feeding activities. Once established, it can be vertically transmitted through FAW eggs, suggesting the potential that FAW can convert maize-derived endophytes into symbiotic bacteria for intergenerational transmission. The prevalence of P. dispersa in FAW guts and maize leaves was also confirmed over large geographic regions, indicating its evolutionary adaptation in fields. Bxs determination in the gut and frass of FAW combined with bioassays performance on maize bx2 mutants revealed that the colonization of P. dispersa can promote FAW growth by metabolizing Bxs rather than other metabolites. Additionally, genome and transcriptome analyses identified plasmid-borne genes, rather than chromosomes of this species, were crucial for Bxs metabolism. This was further validated through in vitro prokaryotic expression assays by expressing two candidate genes form the plasmid.

CONCLUSIONS

FAW can convert maize endophytes into its own probiotics to detoxify Bxs and thus enhance caterpillar growth. This represents a novel strategy for lepidopteran pests-transforming allies of the host into its own-thereby shedding light on the rapid spread of FAW and enhancing our understanding of ecological and evolutionary mechanisms underlying the pest-microbe-plant interactions. Video Abstract.

A smooth vetch (Vicia villosa var.) strain endogenous to the broad-spectrum antagonist Bacillus siamensis JSZ06 alleviates banana wilt disease

Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense Tropical Race 4 (Foc TR4), poses a significant threat to banana production globally, thereby necessitating effective biocontrol methods to manage this devastating disease. This study investigates the potential of Bacillus siamensis strain JSZ06, isolated from smooth vetch, as a biocontrol agent against Foc TR4. To this end, we conducted a series of in vitro and in vivo experiments to evaluate the antifungal activity of strain JSZ06 and its crude extracts. Additionally, genomic analyses were performed to identify antibiotic synthesis genes, while metabolomic profiling was conducted to characterize bioactive compounds. The results demonstrated that strain JSZ06 exhibited strong inhibitory activity against Foc TR4, significantly reducing mycelial growth and spore germination. Moreover, scanning and transmission electron microscopy revealed substantial ultrastructural damage to Foc TR4 mycelia treated with JSZ06 extracts. Genomic analysis identified several antibiotic synthesis genes, and metabolomic profiling revealed numerous antifungal metabolites. Furthermore, in pot trials, the application of JSZ06 fermentation broth significantly enhanced banana plant growth and reduced disease severity, achieving biocontrol efficiencies of 76.71% and 79.25% for leaves and pseudostems, respectively. In conclusion, Bacillus siamensis JSZ06 is a promising biocontrol agent against Fusarium wilt in bananas, with its dual action of direct antifungal activity and plant growth promotion underscoring its potential for integrated disease management strategies.

A biological product of Bacillus amyloliquefaciens QST713 strain for promoting banana plant growth and modifying rhizosphere soil microbial diversity and community composition

Introduction

Bananas are not only an important food crop for developing countries but also a major trading fruit for tropical and semitropical regions, maintaining a huge trade volume. Fusarium wilt of banana (FWB) caused by Fusarium oxysporum f. sp. cubense is becoming a serious challenge to the banana industry globally. Biological control has the potential to offer both effective and sustainable measures for this soil-borne disease.

Methods

In order to explore the biocontrol effects of the biological agent Bacillus amyloliquefaciens QST713 strain on banana plants, two cultivars, Brazilian and Yunjiao No. 1, with varied resistance to FWB, were used in greenhouse pot experiments.

Results

Results showed that the plant height and pseudostem diameter of banana-susceptible cultivar Brazilian increased by 11.68% and 11.94%, respectively, after QST713 application, while the plant height and pseudostem diameter of resistant cultivar Yunjiao No. 1 increased by 14.87% and 12.51%, respectively. The fresh weight of the two cultivars increased by 20.66% and 36.68%, respectively, indicating that this biological agent has potential effects on plant growth. Analysis of the rhizosphere soil microbial communities of two different cultivars of banana plants showed that TR4 infection and B. amyloliquefaciens QST713 strain application significantly affected the bacterial and fungal diversity of Yunjiao No. 1, but not in the cultivar Brazilian. In addition, TR4 infection and QST713 application changed the bacterial community composition of both banana cultivars, and the fungal community composition of Yunjiao No. 1 also changed significantly. Relevance analysis indicated that the relative richness of Bacillus and Pseudomonas in the rhizosphere of both cultivars increased significantly after QST713 application, which had a good positive correlation with plant height, pseudostem girth, aboveground fresh weight, leaf length, and leaf width.

Discussion

Therefore, the outcome of this study suggests that the biological agent QST713 strain has potential application in banana production for promoting plant growth and modification of soil microbial communities, particularly in the TR4-infected field.

Banana disease-suppressive soil drives Bacillus assembled to defense Fusarium wilt of banana

Fusarium wilt of banana (FWB) caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), poses a serious problem for sustainable banana production. Biological control is one of the effective measures to control this destructive disease. High-throughput sequencing of soil microorganisms could significantly improve the efficiency and accuracy of biocontrol strain screening. In this study, the soil microbial diversity of six main banana-producing areas in Yunnan was sequenced by Illumina Miseq platform. The outcome of this study showed the genus of Chujaibacter, Bacillus, and Sphingomonas were significantly enriched in microorganism community composition. Further correlation analysis with soil pathogen (Foc TR4) content showed that Bacillus was significantly negatively correlated with pathogen content. Therefore, we isolated and identified Bacillus from the disease-suppressive soils, and obtained a B. velezensis strain YN1910. In vitro and pot experiments showed that YN1910 had a significant control effect (78.43-81.76%) on banana Fusarium wilt and had a significant growth promotion effect on banana plants.

Bacillus velezensis RC116 Inhibits the Pathogens of Bacterial Wilt and Fusarium Wilt in Tomato with Multiple Biocontrol Traits

Soil-borne plant diseases seriously threaten the tomato industry worldwide. Currently, eco-friendly biocontrol strategies have been increasingly considered as effective approaches to control the incidence of disease. In this study, we identified bacteria that could be used as biocontrol agents to mitigate the growth and spread of the pathogens causing economically significant diseases of tomato plants, such as tomato bacterial wilt and tomato Fusarium wilt. Specifically, we isolated a strain of Bacillus velezensis (RC116) from tomato rhizosphere soil in Guangdong Province, China, with high biocontrol potential and confirmed its identity using both morphological and molecular approaches. RC116 not only produced protease, amylase, lipase, and siderophores but also secreted indoleacetic acid, and dissolved organophosphorus in vivo. Moreover, 12 Bacillus biocontrol maker genes associated with antibiotics biosynthesis could be amplified in the RC116 genome. Extracellular secreted proteins of RC116 also exhibited strong lytic activity against Ralstonia solanacearum and Fusarium oxysporum f. sp. Lycopersici. Pot experiments showed that the biocontrol efficacy of RC116 against tomato bacteria wilt was 81%, and consequently, RC116 significantly promoted the growth of tomato plantlets. Based on these multiple biocontrol traits, RC116 is expected to be developed into a broad-spectrum biocontrol agent. Although several previous studies have examined the utility of B. velezensis for the control of fungal diseases, few studies to date have evaluated the utility of B. velezensis for the control of bacterial diseases. Our study fills this research gap. Collectively, our findings provide new insights that will aid the control of soil-borne diseases, as well as future studies of B. velezensis strains.

Biohardening of Banana cv. Karpooravalli (ABB; Pisang Awak) With Bacillus velezensis YEBBR6 Promotes Plant Growth and Reprograms the Innate Immune Response Against Fusarium oxysporum f.sp. cubense

Induction of innate immune response and growth promotion in banana by B. velezensis against Foc.