Plant growth-promoting rhizobacteria and Trichoderma shift common vetch(Vicia sativa)physiology and phyllosphere bacteria toward antagonism against anthracnose caused by Colletotrichum spinaciae

Background:Plant phyllosphere microbes are important for the host plant's protection.Plant growth-promoting rhizobacteria(PGPR)and Trichoderma are common biocontrol agents(BCAs)for disease management.Pathogens and BCAs can change the rhizosphere microbial composition;however,the effect of PGPR or Trichoderma on plant phyllosphere microbes,particularly for mesocosms involving the interaction between pathogens and BCAs,is not well known.Methods:High-throughput sequencing was used to identify the phyllosphere bacterial community of common vetch interacting with Colletotrichum spinaciae,two PGPRs(Bacillus subtilis and Bacillus licheniformis),and Trichoderma longibrachiatum.We evaluated anthracnose severity,phyllosphere bacteria diversity and composition,and the relationship between the activities of plant defense enzymes and hormonal molecules in plants treated with individual and combined inoculations of PGPRs,Trichoderma,and C.spinaciae.Results:PGPR or Trichoderma alone reduced disease severity.Trichoderma reduced the salicylic acid content,PGPR increased the catalase activity in plants,and co-inoculation of PGPR and Trichoderma decreased the salicylic acid content.Inoculation of PGPR and Trichoderma individually or in combination changed the disease-associated phyllosphere bacteria,and this effect was related to plant defense enzymes and hormonal molecules.Conclusions:We suggest that the plant defense response induced by PGPR and Trichoderma results in the enrichment of a fraction of favorable chloroplastic bacteria,which facilitates plant defense against diseases.

Screening of Antagonistic Bacteria from Phyllosphere towards Tobacco Brown Spot Fungus Alternaria alternata

The possibility of employing antagonistic bacteria for the control of tobacco brown spot was studied. Approximately 136 strains of bacteria were isolated from phyllospheres of tobacco and 9 of these possessed high levels of antagonistic properties, They significantly reduced brown spot in detached tobacco leaves when artificially inoculated with Alternaria alternata. Culture filtrate of the most effective bacterial isolate which designated as Tpb88 was shown to be very efficient in inhibiting mycelial growth of A alternata in dual cultures. Culture filtrate of Tpb88 inhibited germination and germ tube elongation of A alternata. The results showed that the culture filtrate directly inhibited spore germination of A alternata, especially during the first hours of the paired cultivation. The rate of antagonistic activity of culture filtrate of Tpb88 depended on its concentration in the mixture. The greatest inhibition of spore germination was ob served at the highest concentration of filtrate （filtrate to fungal spores inocula mixed in proportion 1 ： 50）. These suggest that the hypothetic mechanism of Tpb88 against tobacco brown spot is to produce antagonistic substances.

Host plant traits play a crucial role in shaping the composition of epiphytic microbiota in the arid desert,Northwest China

Phyllosphere microorganisms are a crucial component of environmental microorganisms,highly influenced by host characteristics,and play a significant role in plant health and productivity.Nonetheless,the impact of host characteristics on shaping phyllosphere microbial communities of plants with different life forms remains ambiguous.Utilizing high-throughput sequencing technology,this study analyzed the diversity and community composition of phyllosphere epiphytic microorganisms(e.g.,bacteria and fungi)of various plant life forms in the hinterland of the Gurbantunggut Desert,Northwest China.Functional annotation of prokaryotic taxa(FAPROTAX)and fungi function guild(FUNGuild)were employed to assess the ecological functions of microorganisms and to investigate the role of stochastic and deterministic processes in shaping phyllosphere microbial communities.Result showed a diverse array of phyllosphere epiphytic microorganisms in the desert plants,with Proteobacteria,Cyanobacteria,and Actinobacteriota dominating bacterial community,while Ascomycota and Basidiomycota were prevalent in fungal community.Comparison across different plant life forms highlighted distinct microbial communities,indicating strong filtering effects by plant characteristics.FAPROTAX prediction identified intracellular parasites(accounting for 27.44%of bacterial community abundance),chemoheterotrophy(10.12%),and phototrophy(17.41%)as the main functions of epiphytic bacteria on leaves of different life form plants.FUNGuild prediction indicated that phyllosphere epiphytic fungi primarily served as Saprotrophs(81.77%),Pathotrophs(17.41%),and Symbiotrophs(0.82%).Co-occurrence network analysis demonstrated a predominance of positive correlations among different microbial taxa.Raup-Crick dissimilarity index analysis revealed that deterministic processes predominantly influenced phyllosphere bacterial and fungal community assembly.Variance partitioning analysis and random forest modeling suggested that plant leaf functional traits significantly impacted both bacterial and fungal community composition,with fungal community composition showing a closer association with leaf nutrients and physiology compared with bacterial community composition.The distinct responses of bacterial and fungal communities to plant traits were attributed to the differing properties of bacteria and fungi,such as bacteria having higher potential dispersal rates and broader ecological niches than fungi.Overall,the results indicate that phyllosphere bacterial and fungal communities undergo similar community assembly processes,with fungi being more influenced by plant characteristics than bacteria.These findings offer novel insights into the ecology of phyllosphere microbial communities of desert plants.

Leaf metabolic influence of glyphosate and nanotubes on the Arabidopsis thaliana phyllosphere

Chemical exposure can indirectly affect leaf microbiota communities,but the mechanism driving this phenomenon remains largely unknown.Results revealed that the co-exposure of glyphosate and multi-carbon nanotubes(CNTs)caused a synergistic inhibitory effect on the growth and metabolism of Arabidopsis thaliana shoots.However,only a slight inhibitory effect was induced by nanotubes or glyphosate alone at the tested concentrations.Several intermediate metabolites of nitrogen metabolism and fatty acid synthesis pathways were upregulated under the combined treatment,which increased the amount of energy required to alleviate the disruption caused by the combined treatment.Additionally,compared with the two individual treatments,the glyphosate/nanotube combination treatment induced greater fluctuations in the phyllosphere bacterial community members with low abundance(relative abundance(RA)<1%)at both the family and genus levels,and among these bacteria some plant growth promotion and nutrient supplement related bacteria were markable increased.Strikingly,strong correlations between phyllosphere bacterial diversity and metabolites suggested a potential role of leaf metabolism,particularly nitrogen and carbohydrate metabolism,in restricting the range of leaf microbial taxa.These correlations between phyllosphere bacterial diversity and leaf metabolism will improve our understanding of plant-microbe interactions and the extent of their drivers of variation and the underlying causes of variability in bacterial community composition.

Profile of the culturable microbiome capable of producing acyl-homoserine lactone in the tobacco phyllosphere

Bacterial populations coexisting in the phyllosphere niche have important effects on plant health. Quorum sensing （QS） allows bacteria to communicate via diffusible signal molecules, but QS-dependent behaviors in phyllosphere bacterial populations are poorly understood. We investigate the dense and diverse N-acyl-homoserine lactone （AHL）-producing phyllosphere bacteria living on tobacco leaf surfaces via a culture-dependent method and 16S rRNA gene sequencing. Our results indicated that approximately 7.9%-11.7% of the culturable leaf-associated bacteria have the ability to produce AHL based on the assays using whole-cell biosensors. Sequencing of the 16S rRNA gene assigned the AHL-producing strains to two phylogenetic groups, with Gammaproteobacteria （93%） as the predominant group, followed by Alphaproteobacteria. All of the AHL-producing Alphaproteobacteria were affiliated with the genus Rhizobium, whereas the AHL-producing bacteria belonging to the Gammaproteobacteria mainly fell within the genera Pseudomonas, Acinetobacter, Citrobacter, Enterobacter, Pantoea and Serratia. The bioassays of supernatant extracts revealed that a portion of the strains have a remarkable AHL profile for AHL induction activity using the two different biosensors, and one compound in the active extract of a representative isolate, NTL223, corresponded to 3-oxo-hexanoyl-homoserine lactone. A large population size and diversity of bacteria capable of AHL-driven QS were found to cohabit on leaves, implying that cross-communication based AHL-type QS may be common in the phyllosphere. Furthermore, this study provides a general snapshot of a potential valuable application of AHL-producing bacteria inhabiting leaves for their presumable ecological roles in the phyllosphere.