Legume-rhizobia interactions in a complex microbiome

Biological nitrogen fixation is important for agriculture, carbon sequestration, and ecosystem restoration. This is primarily conducted by rhizobia (nitrogen fixing bacteria) in association with legume plants. Most research in improving rhizobial strains involves single strain experiments. However, improved metagenomics methods have demonstrated considerable differences between single strain inoculations and strain behaviour when exposed to a complex microbiome. To identify some these differences, this experiment applies two treatment factors in a controlled environment of containers with autoclaved sand. All main experimental containers were inoculated with several strains of Bradyrhizobia japonicum. The first treatment factor was the planting of surface-sterilised seedlings of host plant Acacia acuminata; the second treatment factor was inoculation with an external soil microbiome. Several negative controls without planting or inoculation were also present. A novel method of whole genome metagenomic sequencing to observe known strain abundance, without amplification or culturing, was developed. Using this method, abundance patterns of these B. japonicum strains were compared between initial inoculation and the end of a growth period of several weeks. Analysis reveals a single strain as the preferred nodulation strain within this experiment, but also shows that all strains inoculated continued to persist in the substrate at detectable levels. The use of long reads with the MinION DNA sequencer also allowed the potential of identification of horizontal gene transfer events. None were detected in an initial screen, but a framework for further inspection of this dataset for such events is described

Kondo Metal and Ferrimagnetic Insulator on the Triangular Kagom\'e Lattice

We obtain the rich phase diagrams in the Hubbard model on the triangular Kagom\'e lattice as a function of interaction, temperature and asymmetry, by combining the cellular dynamical mean-field theory with the continuous time quantum Monte Carlo method. The phase diagrams show the asymmetry separates the critical points in Mott transition of two sublattices on the triangular Kagom\'e lattice and produces two novel phases called plaquette insulator with an obvious gap and a gapless Kondo metal. When the Coulomb interaction is stronger than the critical value Uc, a short range paramagnetic insulating phase, which is a candidate for the short rang resonating valence-bond spin liquid, emerges before the ferrimagnetic order is formed independent of asymmetry. Furthermore, we discuss how to measure these phases in future experiments

Microstructural and Mechanical-Property Manipulation through Rapid Dendrite Growth and Undercooling in an Fe-based Multinary Alloy

Rapid dendrite growth in single- or dual-phase multicomponent alloys can be manipulated to improve the mechanical properties of such metallic materials. Rapid growth of (αFe) dendrites was realized in an undercooled Fe-5Ni-5Mo-5Ge-5Co (wt.%) multinary alloy using the glass fluxing method. The relationship between rapid dendrite growth and the micro-/nano-mechanical properties of the alloy was investigated by analyzing the grain refinement and microstructural evolution resulting from the rapid dendrite growth. It was found that (αFe) dendrites grow sluggishly within a low but wide undercooling range. Once the undercooling exceeds 250 K, the dendritic growth velocity increases steeply until reaching a plateau of 31.8 ms[superscript −1]. The increase in the alloy Vickers microhardness with increasing dendritic growth velocity results from the hardening effects of increased grain/phase boundaries due to the grain refinement, the more homogeneous distribution of the second phase along the boundaries, and the more uniform distribution of solutes with increased contents inside the grain, as verified also by nanohardness maps. Once the dendritic growth velocity exceeds ~8 ms[superscript −1], the rate of Vickers microhardness increase slows down significantly with a further increase in dendritic growth velocity, owing to the microstructural transition of the (αFe) phase from a trunk-dendrite to an equiaxed-grain microstructure.Singapore-MIT Allianc

Four complete genome sequences for Bradyrhizobium sp. strains isolated from an endemic Australian Acacia legume reveal structural variation

Bradyrhizobium sp. strains were isolated from root nodules of the Australian legume, Acacia acuminata (Fabaceae). Here, we report the complete genome sequences of four strains using a hybrid long- and short-read assembly approach. The genome sizes range between;7.1Mbp and;8.1Mbp, each with one single circular chromosome. Whole-genome alignments show extensive structural rearrangement

Fracture mode control: a bio-inspired strategy to combat catastrophic damage

The excellent mechanical properties of natural biomaterials have attracted intense attention from researchers with focus on the strengthening and toughening mechanisms. Nevertheless, no material is unconquerable under sufficiently high load. If fracture is unavoidable, constraining the damage scope turns to be a practical way to preserve the integrity of the whole structure. Recent studies on biomaterials have revealed that many structural biomaterials tend to be fractured, under sufficiently high indentation load, through ring cracking which is more localized and hence less destructive compared to the radial one. Inspired by this observation, here we explore the factors affecting the fracture mode of structural biomaterials idealized as laminated materials. Our results suggest that fracture mode of laminated materials depends on the coating/substrate modulus mismatch and the indenter size. A map of fracture mode is developed, showing a critical modulus mismatch (CMM), below which ring cracking dominates irrespective of the indenter size. Many structural biomaterials in nature are found to have modulus mismatch close to the CMM. Our results not only shed light on the mechanics of inclination to ring cracking exhibited by structural biomaterials but are of great value to the design of laminated structures with better persistence of structural integrity.Research Grants Council (Hong Kong, China). Early Career Scheme (Grant 533312)Hong Kong Polytechnic University. Departmental General Research Funds (Internal Competitive Research Grants 4-ZZA8)Hong Kong Polytechnic University. Departmental General Research Funds (Internal Competitive Research Grants A-PM24)Hong Kong Polytechnic University. Departmental General Research Funds (Internal Competitive Research Grants G-UA20

Rolling behavior of a micro-cylinder in adhesional contact

Understanding the rolling behavior of a micro-object is essential to establish the techniques of micro-manipulation and micro-assembly by mechanical means. Using a combined theoretical/computational approach, we studied the critical conditions of rolling resistance of an elastic cylindrical micro-object in adhesional contact with a rigid surface. Closed-form dimensionless expressions for the critical rolling moment, the initial rolling contact area, and the initial rolling angle were extracted after a systematic parametric study using finite element method (FEM) simulations. The total energy of this system is defined as the sum of three terms: the elastic energy stored in the deformed micro-cylinder, the interfacial energy within the contact area, and the mechanical potential energy that depends on the external moment applied to the cylindrical micro-object. A careful examination of the energy balance of the system surprisingly revealed that the rolling resistance per unit cylindrical length can be simply expressed by “work of adhesion times cylindrical radius” independent of the Young’s modulus. In addition, extending a linear elastic fracture mechanics based approach in the literature, we obtained the exact closed-form asymptotic solutions for the critical conditions for initial rolling; these asymptotic solutions were found in excellent agreement with the full-field FEM results.Singapore-MIT Allianc