Global-level population genomics reveals differential effects of geography and phylogeny on horizontal gene transfer in soil bacteria.

Although microorganisms are known to dominate Earth's biospheres and drive biogeochemical cycling, little is known about the geographic distributions of microbial populations or the environmental factors that pattern those distributions. We used a global-level hierarchical sampling scheme to comprehensively characterize the evolutionary relationships and distributional limitations of the nitrogen-fixing bacterial symbionts of the crop chickpea, generating 1,027 draft whole-genome sequences at the level of bacterial populations, including 14 high-quality PacBio genomes from a phylogenetically representative subset. We find that diverse Mesorhizobium taxa perform symbiosis with chickpea and have largely overlapping global distributions. However, sampled locations cluster based on the phylogenetic diversity of Mesorhizobium populations, and diversity clusters correspond to edaphic and environmental factors, primarily soil type and latitude. Despite long-standing evolutionary divergence and geographic isolation, the diverse taxa observed to nodulate chickpea share a set of integrative conjugative elements (ICEs) that encode the major functions of the symbiosis. This symbiosis ICE takes 2 forms in the bacterial chromosome-tripartite and monopartite-with tripartite ICEs confined to a broadly distributed superspecies clade. The pairwise evolutionary relatedness of these elements is controlled as much by geographic distance as by the evolutionary relatedness of the background genome. In contrast, diversity in the broader gene content of Mesorhizobium genomes follows a tight linear relationship with core genome phylogenetic distance, with little detectable effect of geography. These results illustrate how geography and demography can operate differentially on the evolution of bacterial genomes and offer useful insights for the development of improved technologies for sustainable agriculture.

Metallic glass ultrathin films with hierarchical structure and their dynamic and thermodynamic behavior.

Metallic glass (MG) ultrathin films with hierarchical structure were in situ grown and characterized by scanning tunneling microscopy. A reversible dynamic behavior is observed at 77 K indicating a high mobility within the Fe85Sc15 MG ultrathin films. The complete scheme of the phase transition from amorphous solid to supercooled liquid and further to the crystalline phase is depicted. We find Fe85Sc15 MG ultrathin films with a reduction of the glass transition temperature of ∼290 K and an expanded temperature window of the supercooled liquid region of 180 K, which is almost 6 times larger than that of the conventional bulk MG with identical composition.

Graphene tailored by Fe3O4 nanoparticles: low-adhesive and durable superhydrophobic coatings.

This study reports stable superhydrophobic Fe3O4/graphene hybrid coatings prepared by spin coating of the Fe3O4/graphene/PDMS mixed solution on titanium substrates. By tailoring graphene sheets with Fe3O4 nanoparticles, the superhydrophobicity of graphene platelets was largely enhanced with a water contact angle of 164° and sliding angle <2°. Fe3O4 nanoparticles interact with FLG sheets via Fe-O-C covalent link, to form a graphene micro-sheet pinned strongly by nano-sized Fe3O4. The newly-formed micro/nano-structured sheets interact with each other via strong dipole-dipole attractions among Fe3O4 nanoparticles, confirmed by the blue shifts of G band observed in Raman spectra. The strongly interactive micro/nano-structured sheets are responsible for the improvement of both the surface hydrophobicity and the durability towards water impacting. The obtained hybrid coatings possess excellent durability in various environments, such as acidic and basic aqueous solutions, simulating ocean water. And also the coatings can retain their stable superhydrophobicity in Cassie-Baxter state even after annealing at 250 °C or refrigerating at -39 °C for 10 h. We employed an AFM to probe nanoscale adhesion forces to examine further the ability of the as-prepared coatings to resist the initial formation of water layers which reflects the ability to prevent the water spreading. The most superhydrophobic and durable hybrid coating with 1.8 g Fe3O4, shows the smallest adhesion force, as expected, indicating this surface possesses the weakest initial water adhesive strength. The resulting low-adhesive superhydrophobic coating shows a good self-cleaning ability. This fabrication of low-adhesive and durable superhydrophobic Fe3O4/FLG hybrid coatings advances a better understanding of the physics of wetting and yield a prospective candidate for various practical applications, such as self-cleaning, microfluidic devices, etc.

Enhanced intravenous transgene expression in mouse lung using cyclic-head cationic lipids.

Herein, we report enhanced intravenous mouse lung transfection using novel cyclic-head-group analogs of usually open-head cationic transfection lipids. Design and synthesis of the new cyclic-head lipid N,N-di-n-tetradecyl-3,4-dihydroxy-pyrrolidinium chloride (lipid 1) and its higher alkyl-chain analogs (lipids 2-4) and relative in vitro and in vivo gene transfer efficacies of cyclic-head lipids 1-4 to their corresponding open-head analogs [lipid 5, namely N,N-di-n-tetradecyl-N,N-(2-hydroxyethyl)ammonium chloride and its higher alkyl-chain analogs, lipids 6-8] have been described. In stark contrast to comparable in vitro transfection efficacies of both the cyclic- and open-head lipids, lipids 1-4 with cyclic heads were found to be significantly more efficient (by 5- to 11-fold) in transfecting mouse lung than their corresponding open-head analogs (5-8) upon intravenous administration. The cyclic-head lipid 3 with di-stearyl hydrophobic tail was found to be the most promising for future applications.