Attractant and repellent induce opposing changes in the four-helix bundle ligand-binding domain of a bacterial chemoreceptor.

Motile bacteria navigate toward favorable conditions and away from unfavorable environments using chemotaxis. Mechanisms of sensing attractants are well understood; however, molecular aspects of how bacteria sense repellents have not been established. Here, we identified malate as a repellent recognized by the MCP2201 chemoreceptor in a bacterium Comamonas testosteroni and showed that it binds to the same site as an attractant citrate. Binding determinants for a repellent and an attractant had only minor differences, and a single amino acid substitution in the binding site inverted the response to malate from a repellent to an attractant. We found that malate and citrate affect the oligomerization state of the ligand-binding domain in opposing way. We also observed opposing effects of repellent and attractant binding on the orientation of an alpha helix connecting the sensory domain to the transmembrane helix. We propose a model to illustrate how positive and negative signals might be generated.

Three-Dimensional Zinc-Seeded Carbon Nanofiber Architectures as Lightweight and Flexible Hosts for a Highly Reversible Zinc Metal Anode.

Uneven zinc (Zn) deposition typically leads to uncontrollable dendrite growth, which renders an unsatisfactory cycling stability and Coulombic efficiency (CE) of aqueous zinc ion batteries (ZIBs), restricting their practical application. In this work, a lightweight and flexible three-dimensional (3D) carbon nanofiber architecture with uniform Zn seeds (CNF-Zn) is prepared from bacterial cellulose (BC), a kind of biomass with low cost, environmental friendliness, and abundance, as a host for highly reversible Zn plating/stripping and construction of high-performance aqueous ZIBs. The as-prepared 3D CNF-Zn with a porous interconnected network significantly decreases the local current density, and the functional Zn seeds provide uniform nuclei to guide the uniform Zn deposition. Benefiting from the synergistic effect of Zn seeds and the 3D porous framework in the flexible CNF-Zn host, the electrochemical performance of the as-constructed ZIBs is significantly improved. This flexible 3D CNF-Zn host delivers a high and stable CE of 99.5% over 450 cycles, ensuring outstanding rate performance and a long cycle life of over 500 cycles at 4 A g-1 in the CNF-Zn@Zn//NaV3O8·1.5H2O full battery. More importantly, owing to the flexibility of the 3D CNF-Zn host, the as-assembled pouch cell shows outstanding mechanical flexibility and excellent energy storage performance. This strategy of producing readily accessible carbon from biomass can be employed to develop advanced functional nanomaterials for next-generation flexible energy storage devices.

Crystal structure of the chromosome partition protein MukE homodimer.

The SMC (structural maintenance of chromosomes) proteins are known to be involved in chromosome pairing or aggregation and play an important role in cell cycle and division. Different from SMC-ScpAB complex maintaining chromosome structure in most bacteria, the MukB-MukE-MukF complex is responsible for chromosome condensation in E. coli and some γ-proteobacter. Though different models were proposed to illustrate the mechanism of how the MukBEF complex worked, the assembly of the MukBEF complex is a key. The MukE dimer interacted with the middle region of one MukF molecule, and was clamped by the N- and C-terminal domain of the latter, and then was involved in the interaction with the head domain of MukB. To reveal the structural basis of MukE involved in the dynamic equilibrium of potential different MukBEF assemblies, we determined the MukE structure at 2.44 Å resolution. We found that the binding cavity for the α10, ß4 and ß5 of MukF (residues 296-327) in the MukE dimer has been occupied by the α9 and ß7 strand of MukE. We proposed that the highly dynamic C-terminal region (173-225) was important for the MukE-F assembly and then involved in the MukBEF complex formation.

[Vegetation carbon stocks and net primary productivity of the mangrove forests in Shenzhen, China.] / æ·±åœ³ç¦ç”°çº¢æ ‘æž—æ¤è¢«ç¢³å‚¨é‡å’Œå‡€åˆçº§ç”Ÿäº§åŠ›.

Mangroves are the most important coastal blue carbon sinks. The accurate estimation on the carbon sequestration capacity of plant communities would guide the mangrove conservation, afforestation and management. This study investigated the vegetation carbon stocks of dominant mangrove communities, which were Avicennia marina, Kandelia obovata, Sonneratia caseolaris, and Sonneratia apetala in Futian Nature Mangrove Reserve in Shenzhen, Guangdong Province of China. Vegetation carbon stock consisted of living trees (aboveground and belowground biomass), understory, pneumatophore, standing dead trees, fallen dead trees and litter in these communities. The net primary productivity (NPP) was calculated from the litterfall and incremental growth in the same year of each community. Our results showed that the vegetation carbon stocks for A. marina, K. obovata, S. caseolaris, and S. apetala communities were 28.7, 127.6, 100.1, and 73.6 t C·hm-2, and the NPP were 8.75, 7.67, 9.60, and 11.8 t C·hm-2·a-1, respectively. Therefore, acting as urban forests, Futian mangroves in Shenzhen assimilated about 4000 t CO2·a-1. These results provided guidance for mangrove blue carbon assessment, and theoretical basis for the construction of coastal carbon sequestration forests in China.