Genomic and Functional Characterization of the Endophytic Bacillus subtilis 7PJ-16 Strain, a Potential Biocontrol Agent of Mulberry Fruit Sclerotiniose

Abstract

Bacillus sp. 7PJ-16, an endophytic bacterium isolated from a healthy mulberry stem and previously identified as Bacillus tequilensis 7PJ-16, exhibits strong antifungal activity and has the capacity to promote plant growth. This strain was studied for its effectiveness as a biocontrol agent to reduce mulberry fruit sclerotiniose in the field and as a growth-promoting agent for mulberry in the greenhouse. In field studies, the cell suspension and supernatant of strain 7PJ-16 exhibited biocontrol efficacy and the lowest disease incidence was reduced down to only 0.80%. In greenhouse experiments, the cell suspension (1.0 × 10 and 1.0 × 10 CFU/mL) and the cell-free supernatant (100-fold and 1000-fold dilution) stimulated mulberry seed germination and promoted mulberry seedling growth. In addition, to accurately identify the 7PJ-16 strain and further explore the mechanisms of its antifungal and growth-promoting properties, the complete genome of this strain was sequenced and annotated. The 7PJ-16 genome is comprised of two circular plasmids and a 4,209,045-bp circular chromosome, containing 4492 protein-coding genes and 116 RNA genes. This strain was ultimately designed as Bacillus subtilis based on core genome sequence analyses using a phylogenomic approach. In this genome, we identified a series of gene clusters that function in the synthesis of non-ribosomal peptides (surfactin, fengycin, bacillibactin, and bacilysin) as well as the ribosome-dependent synthesis of tasA and bacteriocins (subtilin, subtilosin A), which are responsible for the biosynthesis of numerous antimicrobial metabolites. Additionally, several genes with function that promote plant growth, such as indole-3-acetic acid biosynthesis, the production of volatile substances, and siderophores synthesis, were also identified. The information described in this study has established a good foundation for understanding the beneficial interactions between endophytes and host plants, and facilitates the further application of B. subtilis 7PJ-16 as an agricultural biofertilizer and biocontrol agent.

A Microbiome Study Reveals Seasonal Variation in Endophytic Bacteria Among different Mulberry Cultivars

“…Also, our group isolated an endophytic Bacillus subtilis 7PJ-16 with strong antagonistic activity from mulberry stem in previous work. This strain not only could effectively control mulberry fruit sclerotiniose in the field, but also promote mulberry seed germination as well as mulberry seedling growth under greenhouse conditions [9]. Furthermore, members of the genus Pantoea [54], Methylobacterium [55], and Pseudomonas [56], dominant genera noted in the present study (Table 1; Fig.…”

“…Notably, endophytic bacteria have the advantage of colonizing, proliferating, and moving within plant tissues and thus are excellent candidates as biocontrol agents [8]. In turn, the host plant provides a protected living space, as well as a constant supply of nutrients for the endophytic bacteria [9,10].…”

The impact of the endophytic bacterial community on mulberry tree growth in the Three Gorges Reservoir ecosystem, China

“…Endophytic bacterial strains with the highest PGP scores were selected and evaluated for their effect on mulberry seedling growth. The disinfection and germination of mulberry seeds (‘GuiSangyou 12’, a cultivar of white mulberry M. alba L.) were carried out using previously described methods (Xu et al ., 2018b). Ten millilitres of each bacterial culture prepared in King's medium (Glickmann and Dessaux, 1995) and adjusted to a concentration of 1.0 × 10 7 colony‐forming units per millilitre (CFU ml −1 ) with sterilized distilled water, were administered to a pot containing 25‐day‐old mulberry seedlings.…”

Biocontrol Potential of a Novel Endophytic Bacterium From Mulberry (Morus) Tree

“…Most of their registered products (e.g., in the EU pesticide database) are based on Bacillus (Berg et al, 2017). There are a number of different reasons for their prevalent use: they present advantages over Gram-negative bacteria due to spores they form, allowing them to survive unfavorable conditions; they are easy to formulate and exhibit a prolonged shelf-life and high temperature stability (Wu et al, 2018;Xu et al, 2018;Zhang et al, 2018). Bacillus species such as Bacillus licheniformis, Bacillus cereus, Bacillus subtilis, Bacillus coagulans, and Bacillus clausii are already used as bacterial antagonists of plant pathogens and as plant growth-promoting bacteria (Cisternas-Jamet et al, 2019;Gautam et al, 2019).…”