Garlic dry rot (GDR), primarily caused by Fusarium proliferatum, is a significant postharvest disease that leads to substantial economic losses. Our previous research demonstrated that supplementing Bacillus-based biocontrol formulations with sucrose could boost its efficiency in protecting plants by building a hostile rhizomicrobiome for destructive soil-borne pathogens. B. velezensis TB918, previously isolated from pepper rhizosphere soil, exhibited a strong in vitro antifungal effect on Fusarium. In this study, we conducted a field experiment to investigate the efficacy of B. velezensis TB918 in controlling GDR, and explored the changes in microbial communities in garlic plants and rhizosphere soil following the application of TB918 with or without sucrose supplementation. Using 16S rRNA and ITS amplicon sequencing, we found that the introduction of TB918 significantly increased the abundance of Pseudomonas in garlic rhizosphere, especially when combined with sucrose. Three Pseudomonas strains were isolated from garlic tissues and rhizosphere soil treated with TB918 and sucrose, among which the GP2 strain exhibited antagonistic effects against pathogen ad planta. Co-culture and colonization assays showed that TB918 facilitated the biofilm formation of Pseudomonas strain by forming consortia. Interestingly, the abundance of potentially non-pathogenic Fusarium concentricum also increased, suggesting a potential niche exclusion effect. Our results demonstrated that TB918 in combination with sucrose effectively reduced the incidence of GDR during storage. This study provides valuable insights into the use of biocontrol agents and sucrose to modulate the garlic microbial community and suppress soil-borne pathogens.

Beneficial rhizobacteria promote plant growth and protect plants against phytopathogens. Effective colonization on plant roots is critical for the rhizobacteria to exert beneficial activities. How bacteria migrate swiftly in the soil of semisolid or solid nature remains unclear. Here we report that sucrose, a disaccharide ubiquitously deployed by photosynthetic plants for fixed carbon transport and storage, and abundantly secreted from plant roots, promotes solid surface motility (SSM) and root colonization by Bacillus subtilis through a previously uncharacterized mechanism. Sucrose induces robust SSM by triggering a signaling cascade, first through extracellular synthesis of polymeric levan, which in turn stimulates strong production of surfactin and hyper-flagellation of the cells. B. subtilis poorly colonizes the roots of Arabidopsis thaliana mutants deficient in root-exudation of sucrose, while exogenously added sucrose selectively shapes the rhizomicrobiome associated with the tomato plant roots, promoting specifically bacilli and pseudomonad. We propose that sucrose activates a signaling cascade to trigger SSM and promote rhizosphere colonization by B. subtilis . Our findings also suggest a practicable approach to boost prevalence of beneficial Bacillus species in plant protection.

本研究利用平板筛选法,从转座子TnYLB-1转化的解淀粉芽孢杆菌Bs-18的突变体文库中筛选到生防作用发生明显变化的3株突变株.以这3株突变株为材料,通过反向PCR技术对突变体中转座子插入位点的侧翼序列进行BLAST比对分析,发现它们与野生芽孢杆菌的芽孢形成、细胞分离、细胞的一系列代谢活动等有关.

Summary Rhizomicrobiome, the communities of microorganisms surrounding the root of the plant, plays a vital role in promoting plant growth and health. The composition of rhizomicrobiome is dynamic both temporally and spatially, and is influenced greatly by the plant host and environmental factors. One of the key influencing factors is rhizodeposits, composed of root‐released tissue cells, exudates, lysates, volatile compounds, etc. Rhizodeposits are rich in carbon and nitrogen elements, and able to select and fuel the growth of rhizomicrobiome. In this minireview, we overview the generation, composition and dynamics of rhizodeposits, and discuss recent work describing the general and specific impacts of rhizodeposits on rhizomicrobiome. We focus further on root exudates, the most dynamic component of rhizodeposits, and review recent progresses about the influence of specific root exudates in promoting bacterial root colonization, inducing biofilm development, acting as plant defence and shaping the rhizomicrobiome.

Bacillus amyloliquefaciens Bs-18 is a biocontrol strains against cucumber powdery mildew with significant control effect. In this paper, the mutant library of Bs-18 was constructed with the shuttle plasmid pMarA carrying transposon TnYLB-1 by the electric shock method to deeply study the molecular mechanism of the biocontrol strain. Through screening transpositional temperature and time, the maximum transpositional success rate was obtained after induced at 50℃ for 16 hours. The mutants were verified by PCR. The construction of Bs-18 mutant library laid a foundation for further study on its biocontrol function genes and mechanism.

To enhance the fermentation level of biocontrol Bacillus,the solid -state fermentation condi-tions of Bacillus subtilis B579 were optimized using response surface methodology to establish the related tech-nology system.Firstly,the Plackett -Burman experiment was applied to screen the importan influential fac-tors,and then the path of steepest ascent was used to approach the biggest region of the cell yield.Moreover, the Box -Benhnken experimental design and response surface methodology were employed to get the regression model,which was proved through regression analysis and practice verification.The results showed that the three factors affecting fermentation production were beef extract,corn meal and soluble starch.The fermenta-tion production reached the highest as 1.93 ×10 11 cfu /g,when the content of beef extract,corn meal and sol-uble starch were 15.1,10.3 and 9.14 g/kg respectively.Under the optimized fermentation conditions,the solid fermentation production of biocontrol Bacillus increased by 15 times compared to the liquid fermentation. The regression model was verified to be accurate and reliable.

利用芽孢杆菌防治植物病害是生物防治的一个重要内容.生防芽孢杆菌种类多,作用范围广,生防芽孢杆菌类微生物制剂能够有效控制植物病害,因此,生防芽孢杆菌在现代农业中有广阔的应用前景.本文就针对生防芽孢杆菌种类及其生防作用机制、国内外生防芽孢杆菌微生物制剂化研究现状及其在应用中存在的问题及对策分析展开简要论述.

To obtain antagonistic bacteria for biocontrol of cucumber powdery mildew , 692 bacterial strains were isolated from different greenhouse soil samples .The strain Bs-18 , which had good inhibitory effect on cucumber powdery mildew with the control effect of 82 .22%, was screened out using plate confrontation method and pot test .Based on the morphological characteristics , physicochemical properties and 16 S rDNA sequence analysis , the strain Bs-18 was identified as Bacillus amyloliquefaciens.

The broad-spectrum polyketide antibiotic 2,4-diacetylphloroglucinol (2,4-DAPG) is a major determinant of the ability of the biocontrol agent Pseudomonas fluorescens 2P24 to exert its suppressive activities towards a variety of soil-borne plant pathogens. Previously, we demonstrated that dysfunction of the transcriptional regulator OmpR of the two-component regulatory system EnvZ/OmpR resulted in elevated 2,4-DAPG production in P fluorescens 2P24. Herein, we provide evidence that OmpR might regulate the transcriptional activity of the hydrolase phlG to influence the intracellular concentrations of 2,4-DAPG. The OmpR deletion mutant PM1102 showed increased transcriptional activity (60%) at the promoter of the phlACBD locus and elevated intracellular concentrations (two-fold) of 2,4-DAPG. A subsequent promoter assay for phlH in PM1102 and for phlG in PM1103 (phlH(-)) showed a negative regulatory relationship for ompR on phlH and for phlH on phlG. Additionally, we used EMSA to establish the direct binding of OmpR to the ompR promoter region and the indirect regulatory relationship of OmpR on phlACBD and phlH transcription. Based on these findings, we propose that OmpR influences the intracellular concentrations of 2,4-DAPG by regulating the transcriptional activity of the hydrolase phlG in P fluorescens 2P24.

Using the colour of colony as the selective marker, the random mutagenesis of mini-Tn5 was per-formed to wild-type biocontrol strain Pseudomonas fluorescens 2P24 for the screening of mutants,which might have altered yields of polyketide metabolite 2,4-diacetylphloroglucinol(2,4-DAPG). The strain Sesu-25 with a increased yield of 2,4-DAPG was screened from the mutant pool. The analysis of flank sequence of transposon implied that the response regulator OmpR of EnvZ/OmpR two-component regulatory system ( TCS ) was disrupted in mutant strain Sesu-25. A DNA fragment harbouring a intact EnvZ/OmpR TCS was obtained by subcloning. The envZ and ompR of P. fluorescens 2P24 shared a identity of 93% and 96% with P. fluorescens F113,respectively. The ompR was ligated into the expression vector pET-22b( +) to obtain the recombinated plasmid pET-ompR,and the plasmid pET-ompR was transformed into E. coli BL21 to generate the strain BL21-ompR. The His-taged OmpR was purified by affinity chromatography and verified by SDS-PAGE electrophoresis analysis.

More than 10 000 bacterial strains were separated from rhizosphere soil of vegetables from Tianjin,Hebei,Shandong,Shanxi,Fujian,Henan and Jiangsu,from which 802 strains exhibiting obvious antagonistic effect on Phytophthora capsici were selected.We further screened 62 strains having better antagonistic effect on Rhizoctonia solani,Botrytis cinerea and Pythium aphanidermatum from these 802 strains.Greenhouse pot experiments against P.capsici show that control effects of 6 strains are higher than 70%,Control effects of strain TB1340,82%,are highest.Determination results of its biology characteristics demonstrate that it has stronger activity producing chitinase,cellulase and β-1,3-glucanase.It is preliminarily identified as Bacillus sp.by 16S rRNA sequence analysis combined with morphology observation.

Three different agricultural residues were evaluated as basic substrates for the production of biological control agent (BCA) Bacillus subtilis strain B579, by solid-state fermentation (SSF). Among them, wheat bran (WB) was shown to be the most suitable substrate, and an initial moisture content of 57% was determined to be optimal for SSF of strain B579. Moreover, employing the Plackett-Burman and Box-Benhnken experimental design models, nine different supplements were investigated to maximize the cell yield. Results demonstrated that a relatively maximal cell yield of 2.12+/-0.03x10(11) CFU/g was achievable utilizing WB as the basic medium supplemented with beef extract (21.3 g kg(-1)), cornmeal (42.6 g kg(-1)), and soluble starch (23.8 g kg(-1)).