An alarming increase in antibiotic-resistant bacterial strains is driving clinical demand for new antibacterial agents. One of the oldest antimicrobial agents is elementary silver (Ag), which has been used for thousands of years. Even today, elementary Ag is used for medical purposes such as treating burns, wounds, and microbial infections. In consideration of the effectiveness of elementary Ag, the present researchers generated effective antibacterial/antibiofilm agents by combining elementary Ag with biocompatible ultrashort peptide compounds. The innovative antibacterial agents comprised a hybrid peptide bound to Ag nanoparticles (IVFK/Ag NPs). These were generated by photoionizing a biocompatible ultrashort peptide, thus reducing Ag ions to form Ag NPs with a diameter of 6 nm. The IVFK/Ag NPs demonstrated promising antibacterial/antibiofilm activity against reference Gram-positive and Gram-negative bacteria compared with commercial Ag NPs. Through morphological changes in Escherichia coli and Staphylococcus aureus, we proposed that the mechanism of action for IVFK/Ag NPs derives from their ability to disrupt bacterial membranes. In terms of safety, the IVFK/Ag NPs demonstrated biocompatibility in the presence of human dermal fibroblast cells, and concentrations within the minimal inhibitory concentration had no significant effect on cell viability. These results demonstrated that hybrid peptide/Ag NPs hold promise as a biocompatible material with strong antibacterial/antibiofilm properties, allowing them to be applied across a wide range of applications in tissue engineering and regenerative medicine.

Non-healing chronic wounds are severe complications, which can often eventually lead to amputations. As such, there is a clear clinical need for dressings that promote the healing of chronic wounds. An advanced wound dressing aims to keep wound tissues moist while offering increased healing rates, preventing scar formation, reducing pain, minimizing infection, improving cosmetics, and lowering overall health care costs. We have previously developed tetrameric peptides Ac-IVZK-NH 2 (Ac-Ile-Val-Cha-Lys-NH 2 ) and Ac-IVFK-NH 2 (Ac-Ile-Val-Phe-Lys-NH 2 ) that self-assemble into nanofibrous hydrogels with biomimetic properties resembling those of collagen. In our study, we tested if these nanogels can fulfill the wound healing criteria mentioned above, and found that the nanogels are suitable scaffolds for encapsulating human dermal fibroblasts. We selected peptide nanogels Ac-IVZK-NH 2 and Ac-IVFK-NH 2 and produced silver nanoparticles in situ within the nanogels to assess their efficacy on micropigs with full-thickness excision wounds. The in situ generation of the silver nanoparticles was done solely through UV irradiation, no reducing agent was used. Application of the peptide nanogels on full thickness micropig wounds demonstrated that the scaffolds are biocompatible and did not trigger wound inflammation. This suggests that the scaffolds are safe for topical application. A comparison of the effect of both nanogels-even without the addition of the silver nanoparticles, revealed that the scaffold itself has a high potential to act as an antibacterial agent, which may suppress both the inflammatory reaction and the activity of proteases. Interestingly, the effect on wound closure of the peptide nanogels was comparable to those of standard care hydrogels. Despite our promising results, there is still much to learn about the molecular basis underlying the efficacy of tetrameric peptide nanogels in wound healing. This will support the urgent demand for advanced treatments of diabetic wounds, based on scientifically and clinically validated studies.

Plants have evolved unique morphological and developmental adaptations to cope with the abiotic stresses imposed by (hyper)arid environments. Such adaptations include the formation of rhizosheath–root system in which mutualistic plant–soil microbiome associations are established: the plant provides a nutrient-rich and shielded environment to microorganisms, which in return improve plant-fitness through plant growth promoting services. We hypothesized that the rhizosheath–root systems represent refuge niches and resource islands for the desert edaphic microbial communities. As a corollary, we posited that microorganisms compete intensively to colonize such “oasis” and only those beneficial microorganisms improving host fitness are preferentially selected by plant. Our results show that the belowground rhizosheath–root micro-environment is largely more hospitable than the surrounding gravel plain soil with higher nutrient and humidity contents, and cooler temperatures. By combining metabarcoding and shotgun metagenomics, we demonstrated that edaphic microbial biomass and community stability increased from the non-vegetated soils to the rhizosheath–root system. Concomitantly, non-vegetated soil communities favored autotrophy lifestyle while those associated with the plant niches were mainly heterotrophs and enriched in microbial plant growth promoting capacities. An intense inter-taxon microbial competition is involved in the colonization and homeostasis of the rhizosheath zone, as documented by significant enrichment of antibiotic resistance genes and CRISPR-Cas motifs. Altogether, our results demonstrate that rhizosheath–root systems are “edaphic mini-oases” and microbial diversity hotspots in hyperarid deserts. However, to colonize such refuge niches, the desert soil microorganisms compete intensively and are therefore prepared to outcompete potential rivals.

We isolated a novel strain, R1DC25T, described as Kaustia mangrovi gen. nov. sp. nov. from the sediments of a mangrove forest on the coast of the Red Sea in Saudi Arabia. This isolate is a moderately halophilic, aerobic/facultatively anaerobic Gram-stain-negative bacterium showing optimum growth at between 30 and 40 °C, at a pH of 8.5 and with 3–5 % NaCl. The genome of R1DC25T comprises a circular chromosome that is 4 630 536 bp in length, with a DNA G+C content of 67.3 mol%. Phylogenetic analyses based on the 16S rRNA gene sequence and whole-genome multilocus sequence analysis of 120 concatenated single-copy genes revealed that R1DC25T represents a distinct lineage within the family Parvibaculaceae in the order Rhizobiales within the class Alphaproteobacteria . R1DC25T showing 95.8, 95.3 and 94.5 % 16S rRNA gene sequence identity with Rhodoligotrophos appendicifer , Rhodoligotrophos jinshengii and Rhodoligotrophos defluvii , respectively. The predominant quinone was Q-10, and the polar lipids were phosphatidylglycerol, phosphatidylcholine, diphosphatidylglycerol, as well as several distinct aminolipids and lipids. The predominant cellular fatty acids were C19 : 0 cyclo ω8c, a combination of C18 : 1 ω7c and/or C18 : 1 ω6c and C16 : 0. On the basis of the differences in the phenotypic, physiological and biochemical characteristics from its known relatives and the results of our phylogenetic analyses, R1DC25T (=KCTC 72348T;=JCM 33619T;=NCCB 100699T) is proposed to represent a novel species in a novel genus, and we propose the name Kaustia mangrovi gen. nov., sp. nov. (Kaustia, subjective name derived from the abbreviation KAUST for King Abdullah University of Science and Technology; mangrovi, of a mangrove).