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 Cellulose is the most prevalent biomass and renewable energy source in nature. The hydrolysis of cellulosic biomass to glucose units is essential for the economic exploitation of this natural resource. Cellulase enzyme, which is largely generated by bacteria and fungus, is commonly used to degrade cellulose. Cellulases are used in a variety of industries, including bioethanol manufacturing, textiles, detergents, drugs, food, and paper. As part of our quest to find an efficient biocatalyst for the hydrolysis of cellulosic biomass, we describe the amplification, cloning, and sequencing of cellulase (cel9z) from Bacillus licheniformis strain Z9, as well as the characterization of the resulting enzyme. Results Cellulase was partially purified from B. licheniformis strain Z9 using (NH4)2SO4 precipitation and Sephadex G-100 gel column chromatography with 356.5 U/mg specific activity, 2.1-purification fold, and 3.07 % yield. The nucleotide sequence of the cellulase gene was deposited to the GenBank, B. licheniformis strain Z9 cellulase (cel9z) gene, under accession number MK814929. This corresponds to 1453 nucleotides gene and encodes for a protein composed of 484 amino acids. Comparison of deduced amino acids sequence to other related cellulases showed that the enzyme cel9z can be classified as a glycoside hydrolase family 9. SDS-PAGE analysis of the purified enzyme revealed that the molecular mass was 54.5 kDa. The optimal enzyme activity was observed at pH 7.4 and 30 °C. The enzyme was found to be strongly inhibited by Mg2+ and Na+, whereas strongly activated by Fe3+, Cu2+, and Ca2+. Conclusions B. licheniformis strain Z9 and its cellulase gene can be further utilized for recombinant production of cellulases for industrial application.
Cellulases are enzymes produced by many organisms and cellulose hydrolysis. They are well-known for their widely distributed industrial and medical uses. In this work, 84 bacterial strains were recovered from agar plates and 24 demonstrated hydrolyzing areas from carboxymethyl cellulose-containing agar dishes following Congo-Red staining. Among the 24 strains, three isolates Z7, Z9 and Z63 have shown increased activity of carboxymethyl cellulase (CMCase). It was shown that the three strains, Bacillus and Klebsiella, belonged to 2 separate genera. The isolates have been morphologically, physiologically, biochemically determined and validated by their 16S rRNA gene sequence. The 16S rRNA sequence of Z7, Z9 and Z63 has been submitted with GenBank under the accession codes (KT693283, KT693282 and KT693284). The sequences have been identified as Bacillus cereus strain Z7, Bacillus licheniformis strain Z9 and Klebsiella oxytoca strain Z63. This study gave appropriate information on the variety of rhizospheric isolated cellulose-degrading bacteria.
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.
Heavy metals, including lead, cause serious damage to human health and the surrounding environment. Natural biosorbents arise as environmentally friendly alternatives. In this study, two of the 41 isolates (8EF and 17OS) were the most efficient bacteria for growing on media supplemented with Pb2+ (1000 mg/L). At high concentrations up to 2000 mg/L, the pioneer isolate 17OS exhibited remarkable resistance to multiheavy metals. This isolate was identified as Paenibacillus dendritiformis 17OS and deposited in GenBank under accession number ON705726.1. Design-Expert was used to optimize Pb2+ metal removal by the tested bacteria. Results indicated that four of six variables were selected using a minimum-run resolution IV experimental design, with a significant affecting Pb2+ removal. Temperature and Pb2+ concentration were significant positive influences, whereas incubation period and agitation speed were significant negative ones. The tested strain modulated the four significant variables for maximum Pb2+ removal using Box–Behnken design. The sequential optimization method was beneficial in increasing biosorption by 4.29%. Dead biomass of P. dendritiformis 17OS was embedded with polyethersulfone to get a hydrophilic adsorptive membrane that can separate Pb2+ easily from aqueous solutions. SEM images and FT-IR analysis proved that the new biosorbent possesses a great structure and a lot of surface functional groups with a negative surface charge of − 9.1 mV. The removal rate of 200 mg/L Pb2+ from water reached 98% using 1.5 g/L of the immobilized biosorbent. The adsorption isotherm studies were displayed to determine the nature of the reaction. The adsorption process was related to Freundlich isotherm which describes the multilayer and heterogeneous adsorption of molecules to the adsorbent surface. In conclusion, dead bacterial cells were immobilized on a polyether sulfone giving it the characteristics of a novel adsorptive membrane for the bioremediation of lead from wastewater. Thus this study proposed a new generation of adsorptive membranes based on polyethersulfone and dead bacterial cells.
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