The application of plant growth-promoting rhizobacteria (PGPR) as vital components for plant growth promotion against biotic and abiotic stresses could be a promising strategy to improve crop production in areas vulnerable to increasing salinity. Here, we isolated Seventy-five endophytic bacteria from roots of healthy Oryza sativa grown in a saline environment of the southern coastal region of Bangladesh. The endophytes in a culture of ~108 CFU/ml showed arrays of plant growth-promoting (PGP) activities: phytohormone (Indole acetic acid) production (1.20–60.13 μg/ ml), nutrient (phosphate) solubilization (0.02–1.81 μg/ml) and nitrogen fixation (70.24–198.70 μg/ml). Four genomically diverse groups were identified namely, Enterobacter, Achromobacter, Bacillus, and Stenotrophomonas using amplified ribosomal DNA restriction analysis followed by their respective 16S rDNA sequence analyses with that of the data available in NCBI GenBank. These four specific isolates showed tolerance to NaCl ranging from 1.37 to 2.57 mol/L in the nutrient agar medium. Under a 200 mmol/L salt stress in vitro, the bacteria in a culture of 108 CFU/ml exhibited competitive exopolysaccharide (EPS) production: Stenotrophomonas (65 μg/ml) and Bacillus (28 μg/ml), when compared to the positive control, Pseudomonas spp. (23.65 μg/ml), a phenomenon ably supported by their strong biofilm-producing abilities both in a microtiter plate assay, and in soil condition; and demonstrated by images of the scanning electron microscope (SEM). Overall, the isolated endophytic microorganisms revealed potential PGP activities that could be supported by their biofilm-forming ability under salinity stress, thereby building up a sustainable solution for ensuring food security in coastal agriculture under changing climate conditions.
The binding of SARS-CoV and SARS-CoV-2 to the ACE2 receptor on human cells is mediated by the spike protein subunit 1 (S1) on the virus surfaces, while the receptor binding domains (RBDs) of S1 are the major determinants for the interaction with ACE2 and dominant targets of neutralizing antibodies. However, at the virus-host interface, additional biomolecular interactions, although being relatively weak in affinity and low in specificity, could also contribute to viral attachment and play important roles in gain- or loss-of-function mutations. In this work, we performed a peptide scanning of the S1 domains of SARS-CoV and SARS-CoV-2 by synthesizing 972 16-mer native and mutated peptide fragments using a high throughput in situ array synthesis technology. By probing the array using fluorescently labelled ACE2, a number of previously unknown potential receptor binding sites of S1 have been revealed. 20 peptides were synthesized using solid phase peptide synthesis, in order to validate and quantify their binding to ACE2. Four ACE2-binding peptides were selected, to investigate whether they can be assembled through a biotinylated peptide/neutravidin system to achieve high affinity to ACE2. A number of constructs exhibited high affinity to ACE2 with Kd values of pM to low nM.
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