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Sun L.,Key Laboratory of Plant Nutrition and Fertilization in Low Middle Reaches of the Yangtze River | Sun L.,Nanjing Agricultural University | Gao J.,Chinese Academy of Agricultural Sciences | Huang T.,Nanjing Agricultural University | And 6 more authors.
FEMS Microbiology Ecology

Microbes are the key components of the soil environment, playing important roles during soil development. Soil parent material provides the foundation elements that comprise the basic nutritional environment for the development of microbial community. After 30 years artificial maturation of cultivation, the soil developments of three different parental materials were evaluated and bacterial community compositions were investigated using the high-throughput sequencing approach. Thirty years of cultivation increased the soil fertility and soil microbial biomass, richness and diversity, greatly changed the soil bacterial communities, the proportion of phylum Actinobacteria decreased significantly, while the relative abundances of the phyla Acidobacteria, Chloroflexi, Gemmatimonadetes, Armatimonadetes and Nitrospira were significantly increased. Soil bacterial communities of parental materials were separated with the cultivated ones, and comparisons of different soil types, granite soil and quaternary red clay soil were similar and different with purple sandy shale soil in both parental materials and cultivated treatments. Bacterial community variations in the three soil types were affected by different factors, and their alteration patterns in the soil development also varied with soil type. Soil properties (except total potassium) had a significant effect on the soil bacterial communities in all three soil types and a close relationship with abundant bacterial phyla. The amounts of nitrogen-fixing bacteria as well as the abundances of the nifH gene in all cultivated soils were higher than those in the parental materials; Burkholderia and Rhizobacte were enriched significantly with long-term cultivation. The results suggested that crop system would not deplete the nutrients of soil parental materials in early stage of soil maturation, instead it increased soil fertility and changed bacterial community, specially enriched the nitrogen-fixing bacteria to accumulate nitrogen during soil development. © FEMS 2015. Source

Wang M.,Key Laboratory of Plant Nutrition and Fertilization in Low Middle Reaches of the Yangtze River | Wang M.,Jiangsu Key Laboratory and Engineering Center for Solid Organic Waste Utilization | Wang M.,Nanjing Agricultural University | Sun Y.,Nanjing Agricultural University | And 9 more authors.
Scientific Reports

Fusarium wilt is caused by the infection and growth of the fungus Fusarium oxysporum in the xylem of host plants. The physiological responses of cucumbers that are infected with Fusarium oxysporum f. sp. cucumerinum (FOC) was studied in pot and hydroponic experiments in a greenhouse. The results showed that although water absorption and stem hydraulic conductance decreased markedly in infected plants, large amounts of red ink accumulated in the leaves of infected cucumber plants. The transpiration rate (E) and stomatal conductance (g s) of the infected plants were significantly reduced, but the E/g s was higher than healthy plants. We further found that there was a positive correlation between leaf membrane injury and E/g s, indicating that the leaf cell membrane injury increased the non-stomatal water loss from infected plants. The fusaric acid (FA), which was detected in the infected plant, resulted in damage to the leaf cell membranes and an increase in E/g s, suggesting that FA plays an important role in non-stomatal water loss. In conclusion, leaf cell membrane injury in the soil-borne Fusarium wilt of cucumber plants induced uncontrolled water loss from damaged cells. FA plays a critical role in accelerating the development of Fusarium wilt in cucumber plants. Source

Weng J.,Nanjing Agricultural University | Weng J.,Key Laboratory of Plant Nutrition and Fertilization in Low Middle Reaches of the Yangtze River | Wang Y.,Nanjing Agricultural University | Wang Y.,Key Laboratory of Plant Nutrition and Fertilization in Low Middle Reaches of the Yangtze River | And 6 more authors.
Applied Microbiology and Biotechnology

Root colonization by antagonistic bacteria is a prerequisite for successful biological control, and the instability of colonization under varying environmental conditions has accentuated the need to improve the colonization activity. Root colonization by Bacillus spp. is mainly determined by chemotaxis and biofilm formation, and both functions are negatively controlled by the global transcription regulator AbrB. Here, we disrupted the gene abrB in Bacillus amyloliquefaciens SQR9, which has been proven to be a promising biocontrol agent of cucumber and watermelon wilt disease. Chemotaxis, biofilm formation, and colonization activities as well as biocontrol efficiency were measured and compared between the wild-type strain of SQR9 and the abrB mutant. The data presented in this article demonstrate that the colonization and biocontrol activity of B. amyloliquefaciens SQR9 could be significantly improved by abrB gene disruption. The results offer a new strategy to enhance the biocontrol efficacy of B. amyloliquefaciens SQR9. © 2012 Springer-Verlag Berlin Heidelberg. Source

Xu Z.,Nanjing Agricultural University | Xu Z.,Key Laboratory of Plant Nutrition and Fertilization in Low Middle Reaches of the Yangtze River | Shao J.,Nanjing Agricultural University | Shao J.,Key Laboratory of Plant Nutrition and Fertilization in Low Middle Reaches of the Yangtze River | And 7 more authors.
Applied and Environmental Microbiology

Bacillus amyloliquefaciens strains are capable of suppressing soilborne pathogens through the secretion of an array of lipopeptides and root colonization, and biofilm formation ability is considered a prerequisite for efficient root colonization. In this study, we report that one of the lipopeptide compounds (bacillomycin D) produced by the rhizosphere strain Bacillus amyloliquefaciens SQR9 not only plays a vital role in the antagonistic activity against Fusarium oxysporum but also affects the expression of the genes involved in biofilm formation. When the bacillomycin D and fengycin synthesis pathways were individually disrupted, mutant SQR9M1, which was deficient in the production of bacillomycin D, only showed minor antagonistic activity against F. oxysporum, but another mutant, SQR9M2, which was deficient in production of fengycin, showed antagonistic activity equivalent to that of the wild-type strain of B. amyloliquefaciens SQR9. The results from in vitro, root in situ, and quantitative reverse transcription-PCR studies demonstrated that bacillomycin D contributes to the establishment of biofilms. Interestingly, the addition of bacillomycin D could significantly increase the expression levels of kinC gene, but KinC activation is not triggered by leaking of potassium. These findings suggest that bacillomycin D contributes not only to biocontrol activity but also to biofilm formation in strain B. amyloliquefaciens SQR9. © 2013, American Society for Microbiology. Source

Zhang N.,Nanjing Agricultural University | Zhang N.,Key Laboratory of Plant Nutrition and Fertilization in Low Middle Reaches of the Yangtze River | Wang D.,Nanjing Agricultural University | Wang D.,Key Laboratory of Plant Nutrition and Fertilization in Low Middle Reaches of the Yangtze River | And 8 more authors.
Plant and Soil

Aim: It is necessary to understand the roles of root exudates involved in plant-microbe interactions to inform practical application of beneficial rhizosphere microbial strains. Methods: Colonization of Bacillus amyloliquefaciens SQR9 (isolated from cucumber rhizosphere) and Bacillus subtilis N11 (isolated from banana rhizosphere) of their original host was found to be more effective as compared to the colonization of the non-host plant. Organic acids in the root exudates of the two plants were identified by High performance liquid chromatography (HPLC). The chemotactic response and effects on biofilm formation were assessed for SQR9 and N11 in response to cucumber and banana root exudates, as well as their organic acids components. Results: Citric acid detected exclusively in cucumber exudates could both attract SQR9 and induce its biofilm formation, whereas only chemotactic response but not biofilm formation was induced in N11. Fumaric acid that was only detected in banana root exudates revealed both significant roles on chemotaxis and biofilm formation of N11, while showing only effects on biofilm formation but not chemotaxis of SQR9. Conclusion: The relationship between PGPR strain and root exudates components of its original host might contribute to preferential colonization. This study advances a clearer understanding of the mechanisms relevant to application of PGPR strains in agricultural production. © 2013 Springer Science+Business Media Dordrecht. Source

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