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Drought is a major threat to crop productivity and causes decreased plant growth, poor yields, and crop failure. Nevertheless, the frequency of droughts is expected to increase in the coming decades. The microbial communities associated with crop plants can influence how plants respond to various stresses; hence, microbiome manipulation is fast becoming an effective strategy for improving the stress tolerance of plants. The effect of drought stress on the root microbiome of perennial woody plants is currently poorly understood. Using Populus trees as a model ecosystem, we found that the diversity of the root microbial community decreased during drought treatment and that compositional shifts in microbes during drought stress were driven by the relative abundances of a large number of dominant phyla, including Actinobacteria, Firmicutes, and Proteobacteria. A subset of microbes, including Streptomyces rochei, Bacillus arbutinivorans, B. endophyticus, B. megaterium, Aspergillus terreus, Penicillium raperi, Trichoderma ghanense, Gongronella butleri, and Rhizopus stolonifer, was isolated from the drought-treated poplar rhizosphere soils, which have potentially beneficial to plant fitness. Further controlled inoculation experiments showed that the isolated bacterial and fungal isolates positively impacted plant growth and drought tolerance. Collectively, our results demonstrate the impact of drought on root microbiome structure and provide a novel example of manipulating root microbiomes to improve plant tolerance.

Recently, cellulose nanocrystals (CNs) have attracted wide attention owing to their superior properties compared to their bulk materials. For example, they represent an outstanding model for fabricating green metallic/metal oxide nanoparticles (NPs). In this study, two CNs (carboxylated CNs and sulfated CNs) extracted from agro-wastes of palm sheath fibers were used as templates for the facile and green synthesis of ZnO NPs by employing the sono-co-precipitation method. The obtained nanomaterials were characterized using TEM, EDX, UV–visible, DLS, FT-IR, and XRD analysis. As a result, the size and concentration of synthesized ZnO NPs were inversely proportional to one another and were affected by the CNs utilized and the reaction temperature used. Contagious diseases incited by multifarious toxigenic bacteria present severe threats to human health. The fabricated bio-nanocomposites were evaluated in terms of their antimicrobial efficacy by agar well diffusion method and broth microdilution assay, showing that CN–ZnO bio-nanocomposites were effective against the tested Gram-negative (Escherichia coli and Salmonella) and Gram-positive (Listeria monocytogenes and Staphylococcus aureus) bacteria. The influence of the subinhibitory concentrations of these suspensions on the expression of the most critical virulence toxin genes of the tested strains was effective. Significant downregulation levels were observed through toxigenic operons to both fabricated CN–ZnO bio-nanocomposites with a fold change ranging from 0.004 to 0.510, revealing a decline in the capacity and virulence of microorganisms to pose infections. Therefore, these newly fabricated CNS–ZnO bio-nanocomposites could be employed rationally in food systems as a novel preservative to inhibit microbial growth and repress the synthesis of exotoxins.

Background Poplar fungal infections are difficult to control and result in severe economic loss. As a viable alternative to chemical pesticides, biocontrol is an effective safe method for disease control. Results Inhibitory activity of Bacillus velezensis 33RB and Aspergillus niger 46SF was evaluated against numerous phytopathogens. The bacterial strain displayed the highest inhibitory activity toward Colletotrichum gloeosporioides BJ02 and Fusarium oxysporum 20RF (61.2 and 49.4%, respectively). Also, the maximum inhibitory activity of A. niger 46SF was exhibited (75.51 and 70.83%) against C. gloeosporioides BJ02 and F. oxysporum 20RF, respectively. The minimum volume (6.25 ml) of sterilized cultural filtrate of bacterial and fungal strains significantly inhibited the growth of C. gloeosporioides BJ02 by 73.3 and 83.3%, respectively, and F. oxysporum 20RF reached 40.4 and 78.8%, respectively. B. velezensis 33RB and A. niger 46SF displayed the highest inhibition toward C. gloeosporioides BJ02 and F. oxysporum 20RF at neutral pH and pH 5, respectively. Moreover, the highest inhibitory activity of B. velezensis 33RB and A. niger 46SF was achieved at 37 °C and 28 °C, respectively. Pathogenicity tests on sterilized detached leaves indicated that these isolates could potentially affect anthracnose and fusarium wilt diseases. Several secondary bioactive metabolites that assured the biocontrol efficacy of tested microbes were detected by liquid chromatography–mass spectrometry (LC–MS). The most detectable compounds included organic acids such as fumaric, DL-malic, citric, isobutyric, and glutamic acids. Also, numerous fatty acids such as lauric, linoleic, oleic, stearic, and myristic acids with diverse biological functions, including antimicrobial properties, were determined. Conclusions Bacillus velezensis 33RB and A. niger 46SF were potential alternatives to chemical pesticides as biological control agents for the phytopathogens C. gloeosporioides BJ02 and F. oxysporum with environmentally friendly and sustainable properties.