Unlocking antagonistic potential of Bacillus amyloliquefaciens KRS005 to control gray mold

Simulated nitrogen deposition enhances resistance of female poplars over males to Pestalotiopsis microspora infection through the recruitment of antagonistic microbes in phyllosphere

Atmospheric nitrogen deposition has globally increased due to human activities and has strongly interfered with plant growth and resistance to biotic stressors. Dioecious plant species have shown secondary dimorphism in growth and development between male and female individuals in response to increased nitrogen deposition. However, the extent to whether these sexual differences influence variations in phyllosphere microbial communities and the associated pathogen resistance between male and female conspecifics remains unclear. To address this knowledge gap, female and male full-sibs of a poplar species were exposed to simulated nitrogen deposition and then artificially infected with a leaf pathogenic fungus, Pestalotiopsis microspora. The findings revealed that simulated nitrogen deposition promoted the growth of both sexes, with male plants exhibiting superior growth. Following P. microspora infection, female control plants displayed a greater leaf lesion area compared to males, but simulated nitrogen deposition reversed this difference. Further phyllosphere microbiome analysis and toxicity test indicated that the sexual differences in pathogen resistance between male and female conspecifics were likely attributable to alterations in the composition and structure of epiphytic microbes as the phyllosphere of female plants harbored a higher abundance of ecologically beneficial microbes with potential biological control capabilities, whereas males exhibited an increase abundance in the phytopathogens genera in response to simulated nitrogen deposition. Confirmatively, two bacterial strains were successfully isolated from the epiphytic phyllosphere of female plants that exhibited strong antagonistic effect against the pathogenic fungus P. microspora in both in vitro and in vivo conditions. The findings have significant implications for the selection of suitable poplar sexes for landscaping and reforestation efforts in areas experienced severe atmospheric nitrogen deposition.

Bacillus lumedeiriae sp. nov., a Gram-Positive, Spore-Forming Rod Isolated from a Pharmaceutical Facility Production Environment and Added to the MALDI Biotyper® Database

A Gram-positive, aerobic, rod-shaped and spore-forming bacterium strain designation, B190/17, was isolated from an air monitoring sample of a Brazilian immunobiological production facility in 2017. The strain was not identifiable by biochemical methodology VITEK® 2 or by MALDI-TOF MS with VITEK® MS RUO and MALDI Biotyper®. The 16S rRNA gene sequencing results showed 98.51% similarity with Bacillus wudalianchiensis FJAT 27215T, 98.28% with 'Bacillus aerolatus' CX 253T, 97.96% with Bacillus badius MTCC 1458T, 97.63% with Bacillus xiapuensis FJAT 46582T and 97.21% with Bacillus thermotolerans SGZ8T. Biochemical data showed that the strain was alanine arylamidase-, Ala-Phe-Pro arylamidase-, ELLMAN (cysteine residues)-, leucine arylamidase-, phenyalanine arylamidase- and tyrosine arylamidase-positive. The genomic DNA G+C% content of B190/17 was 41.6 mol%. The phylogenetic, genomic taxonomy and biochemical tests suggested that B190/17 represents a novel species and should be classified as the type strain of a novel Bacillus species. The name Bacillus lumedeiriae sp. nov. was proposed. After characterization, B190/17 was added to the MALDI Biotyper® database as Bacillus lumedeiriae sp. nov.

Insights into the biocontrol and plant growth promotion functions of Bacillus altitudinis strain KRS010 against Verticillium dahliae

BACKGROUND

Verticillium wilt, caused by the fungus Verticillium dahliae, is a soil-borne vascular fungal disease, which has caused great losses to cotton yield and quality worldwide. The strain KRS010 was isolated from the seed of Verticillium wilt-resistant Gossypium hirsutum cultivar "Zhongzhimian No. 2."

RESULTS

The strain KRS010 has a broad-spectrum antifungal activity to various pathogenic fungi as Verticillium dahliae, Botrytis cinerea, Fusarium spp., Colletotrichum spp., and Magnaporthe oryzae, of which the inhibition rate of V. dahliae mycelial growth was 73.97% and 84.39% respectively through confrontation test and volatile organic compounds (VOCs) treatments. The strain was identified as Bacillus altitudinis by phylogenetic analysis based on complete genome sequences, and the strain physio-biochemical characteristics were detected, including growth-promoting ability and active enzymes. Moreover, the control efficiency of KRS010 against Verticillium wilt of cotton was 93.59%. After treatment with KRS010 culture, the biomass of V. dahliae was reduced. The biomass of V. dahliae in the control group (Vd991 alone) was 30.76-folds higher than that in the treatment group (KRS010+Vd991). From a molecular biological aspect, KRS010 could trigger plant immunity by inducing systemic resistance (ISR) activated by salicylic acid (SA) and jasmonic acid (JA) signaling pathways. Its extracellular metabolites and VOCs inhibited the melanin biosynthesis of V. dahliae. In addition, KRS010 had been characterized as the ability to promote plant growth.

CONCLUSIONS

This study indicated that B. altitudinis KRS010 is a beneficial microbe with a potential for controlling Verticillium wilt of cotton, as well as promoting plant growth.

Plant Growth Promotion and Plant Disease Suppression Induced by Bacillus amyloliquefaciens Strain GD4a

Botrytis cinerea, the causative agent of gray mold disease (GMD), invades plants to obtain nutrients and disseminates through airborne conidia in nature. Bacillus amyloliquefaciens strain GD4a, a beneficial bacterium isolated from switchgrass, shows great potential in managing GMD in plants. However, the precise mechanism by which GD4a confers benefits to plants remains elusive. In this study, an A. thaliana-B. cinerea-B. amyloliquefaciens multiple-scale interaction model was used to explore how beneficial bacteria play essential roles in plant growth promotion, plant pathogen suppression, and plant immunity boosting. Arabidopsis Col-0 wild-type plants served as the testing ground to assess GD4a's efficacy. Additionally, bacterial enzyme activity and targeted metabolite tests were conducted to validate GD4a's potential for enhancing plant growth and suppressing plant pathogens and diseases. GD4a was subjected to co-incubation with various bacterial, fungal, and oomycete pathogens to evaluate its antagonistic effectiveness in vitro. In vivo pathogen inoculation assays were also carried out to investigate GD4a's role in regulating host plant immunity. Bacterial extracellular exudate (BEE) was extracted, purified, and subjected to untargeted metabolomics analysis. Benzocaine (BEN) from the untargeted metabolomics analysis was selected for further study of its function and related mechanisms in enhancing plant immunity through plant mutant analysis and qRT-PCR analysis. Finally, a comprehensive model was formulated to summarize the potential benefits of applying GD4a in agricultural systems. Our study demonstrates the efficacy of GD4a, isolated from switchgrass, in enhancing plant growth, suppressing plant pathogens and diseases, and bolstering host plant immunity. Importantly, GD4a produces a functional bacterial extracellular exudate (BEE) that significantly disrupts the pathogenicity of B. cinerea by inhibiting fungal conidium germination and hypha formation. Additionally, our study identifies benzocaine (BEN) as a novel small molecule that triggers basal defense, ISR, and SAR responses in Arabidopsis plants. Bacillus amyloliquefaciens strain GD4a can effectively promote plant growth, suppress plant disease, and boost plant immunity through functional BEE production and diverse gene expression.