Plant growth promotion and biocontrol properties of a synthetic community in the control of apple disease.

BACKGROUND: Apple Replant Disease (ARD) is common in major apple-growing regions worldwide, but the role of rhizosphere microbiota in conferring ARD resistance and promoting plant growth remains unclear. RESULTS: In this study, a synthetic microbial community (SynCom) was developed to enhance apple plant growth and combat apple pathogens. Eight unique bacteria selected via microbial culture were used to construct the antagonistic synthetic community, which was then inoculated into apple seedlings in greenhouse experiments. Changes in the rhizomicroflora and the growth of aboveground plants were monitored. The eight strains, belonging to the genera Bacillus and Streptomyces, have the ability to antagonize pathogens such as Fusarium oxysporum, Rhizoctonia solani, Botryosphaeria ribis, and Physalospora piricola. Additionally, these eight strains can stably colonize in apple rhizosphere and some of them can produce siderophores, ACC deaminase, and IAA. Greenhouse experiments with Malus hupehensis Rehd indicated that SynCom promotes plant growth (5.23%) and increases the nutrient content of the soil, including soil organic matter (9.25%) and available K (1.99%), P (7.89%), and N (0.19%), and increases bacterial richness and the relative abundance of potentially beneficial bacteria. SynCom also increased the stability of the rhizosphere microbial community, the assembly of which was dominated by deterministic processes (|ß NTI| > 2). CONCLUSIONS: Our results provide insights into the contribution of the microbiome to pathogen inhibition and host growth. The formulation and manipulation of similar SynComs may be a beneficial strategy for promoting plant growth and controlling soil-borne disease.

Mechanisms of nitrogen transformation driven by functional microbes during thermophilic fermentation in an ex situ fermentation system.

In this study, we explored the pathways and mechanisms of nitrogen (N) transformation driven by functional microbes carrying key genes in an ex situ fermentation system (EFS). Temperature and N content were found to be the most important factors driving variation in bacterial and fungal communities, respectively; Bacillus became the most abundant bacteria and Batrachochytrium became the most abundant fungi. Co-occurrence network analysis showed that some bacteria including Halomonas, Truepera, and Gemmatimonas species carry genes that promote mineralization, nitrification, dissimilatory/assimilatory nitrate reduction, denitrification, anammox reactions, and N fixation. The maximum rate of total mineralization reached 136.60 µg N g-1 d-1. Functional microbes promoted various N conversion processes at different rates in the EFS, with levels increasing by at least 0.23 µg N g-1 d-1. These results provide a theoretical basis for feasible optimization measures to address N loss during fermentation.

Populus root exudates are associated with rhizosphere microbial communities and symbiotic patterns.

Introduction: Microbial communities in the plant rhizosphere are critical for nutrient cycling and ecosystem stability. However, how root exudates and soil physicochemical characteristics affect microbial community composition in Populus rhizosphere is not well understood. Methods: This study measured soil physiochemistry properties and root exudates in a representative forest consists of four Populus species. The composition of rhizosphere bacterial and fungal communities was determined by metabolomics and high-throughput sequencing. Results: Luvangetin, salicylic acid, gentisic acid, oleuropein, strigol, chrysin, and linoleic acid were the differential root exudates extracted in the rhizosphere of four Populus species, which explained 48.40, 82.80, 48.73, and 59.64% of the variance for the dominant and key bacterial or fungal communities, respectively. Data showed that differential root exudates were the main drivers of the changes in the rhizosphere microbial communities. Nitrosospira, Microvirga, Trichoderma, Cortinarius, and Beauveria were the keystone taxa in the rhizosphere microbial communities, and are thus important for maintaining a stable Populus microbial rhizosphere. The differential root exudates had strong impact on key bacteria than dominant bacteria, key fungi, and dominant fungi. Moreover, strigol had positively effects with bacteria, whereas phenolic compounds and chrysin were negatively correlated with rhizosphere microorganisms. The assembly process of the community structure (keystone taxa and bacterial dominant taxa) was mostly determined by stochastic processes. Discussion: This study showed the association of rhizosphere microorganisms (dominant and keystone taxa) with differential root exudates in the rhizosphere of Populus plants, and revealed the assembly process of the dominant and keystone taxa. It provides a theoretical basis for the identification and utilization of beneficial microorganisms in Populus rhizosphere.