A Volcano Correlation between Catalytic Activity for Sulfur Reduction Reaction and Fe Atom Count in Metal Center.

Sulfur reduction reaction (SRR) facilitates up to 16 electrons, which endows lithium-sulfur (Li-S) batteries with a high energy density that is twice that of typical Li-ion batteries. However, its sluggish reaction kinetics render batteries with only a low capacity and cycling life, thus remaining the main challenge to practical Li-S batteries, which require efficient electrocatalysts of balanced atom utilization and site-specific requirements toward highly efficient SRR, calling for an in-depth understanding of the atomic structural sensitivity for the catalytic active sites. Herein, we manipulated the number of Fe atoms in iron assemblies, ranging from single Fe atom to diatomic and triatomic Fe atom groupings, all embedded within a carbon matrix. This led to the revelation of a "volcano peak" correlation between SRR catalytic activity and the count of Fe atoms at the active sites. Utilizing operando X-ray absorption and X-ray diffraction spectroscopies, we observed that polysulfide adsorption-desorption and electrochemical conversion kinetics varied up and down with the incremental addition of even a single iron atom to the catalyst's metal center. Our results demonstrate that the metal center with exactly two iron atoms represents the optimal configuration, maximizing atom utility and adeptly handling the conversion of varied intermediate sulfur species, rendering the Li-S battery with a high areal capacity of 23.8 mAh cm-2 at a high sulfur loading of 21.8 mg cm-2. Our results illuminate the pivotal balance between atom utilization and site-specific requirements for optimal electrocatalytic performance in SRR and diverse electrocatalytic reactions.

Characterization of the transcriptional responses of Armillaria gallica 012m to GA3.

Gastrodia elata needs to establish a symbiotic relationship with Armillaria strains to obtain nutrients and energy. However, the signaling cross talk between G. elata and Armillaria strains is still unclear. During our experiment, we found that the vegetative mycelium of Armillaria gallica 012m grew significantly better in the media containing gibberellic acid (GA3) than the blank control group (BK). To explore the response mechanism, we performed an RNA-sequencing experiment to profile the transcriptome changes of A. gallica 012m cultured in the medium with exogenous GA3. The transcriptome-guided differential expression genes (DEGs) analysis of GA3 and BK showed that a total of 1309 genes were differentially expressed, including 361 upregulated genes and 948 downregulated genes. Some of those DEGs correlated with the biological process, including positive regulation of chromosome segregation, mitotic metaphase/anaphase transition, attachment of mitotic spindle microtubules to kinetochore, mitotic cytokinesis, and nuclear division. These analyses explained that GA3 actively promoted the growth of A. gallica to some extent. Further analysis of protein domain features showed that the deduced polypeptide contained 41 candidate genes of GA receptor, and 27 of them were expressed in our samples. We speculate that GA receptors exist in A. gallica 012m. Comparative studies of proteins showed that the postulated GA receptor domains of A. gallica 012m have a higher homologous correlation with fungi than others based on cluster analysis.

Non-trivial Contribution of Carbon Hybridization in Carbon-based Substrates to Electrocatalytic Activities in Li-S Batteries.

Appling an electrochemical catalyst is an efficient strategy for inhibiting the shuttle effect and enhancing the S utilization of Li-S batteries. Carbon-based materials are the most common conductive agents and catalyst supports used in Li-S batteries, but the correlation between the diversity of hybridizations and sulfur reduction reaction (SRR) catalytic activity remains unclear. Here, by establishing two forms of carbon models, i.e., graphitic carbon (GC) and amorphous carbon (AC), we observe that the nitrogen atom doped in the GC possesses a higher local charge density and a lower Gibbs free energy towards the formation of polysulfides than in the AC. And the GC-based electrode consistently inherits considerably enhanced SRR kinetics and superior cycling stability and rate capability in Li-S batteries. Therefore, the function of carbon in Li-S batteries is not only limited as conductive support but also plays an unignorable contribution to the electrocatalytic activities of SRR.

Draft genomic sequence of Armillaria gallica 012m: insights into its symbiotic relationship with Gastrodia elata.

Armillaria species (Basidiomycota, Physalacriaceae) are well known as plant pathogens related to serious root rot disease on various trees in forests and plantations. Interestingly, some Armillaria species are essential symbionts of the rare Chinese medicinal herb Gastrodia elata, a rootless and leafless orchid used for over 2000 years. In this work, an 87.3-M draft genome of Armillaria gallica 012m strain, which was symbiotic with G. elata, was assembled. The genome includes approximately 23.6% repetitive sequences and encodes 26,261 predicted genes. In comparison with other four genomes of Armillaria, the following gene families related to pathogenicity/saprophytic phase, including cytochrome P450 monooxygenases, carbohydrate-active enzyme AA3, and hydrophobins, were significantly contracted in A. gallica 012m. These characteristics may be beneficial for G. elata to get less injuries. The genome-guided analysis of differential expression between rhizomorph (RH) and vegetative mycelium (VM) showed that a total of 2549 genes were differentially expressed, including 632 downregulated genes and 1917 upregulated genes. In the RH, most differentially expressed genes (DEGs) related to pathogenicity were significantly upregulated. To further elucidate gene function, Gene Ontology enrichment analysis showed that the upregulated DEGs significantly grouped into monooxygenase activity, hydrolase activity, glucosidase activity, extracellular region, fungal cell wall, response to xenobiotic stimulus, response to toxic substance, etc. These phenomena indicate that RH had better infection ability than VM. The infection ability of RH may be beneficial for G. elata to obtain nutrition, because the rhizomorph constantly infected the nutritional stems of G. elata and formed the hyphae that can be digested by G. elata. These results clarified the characteristics of A. gallica 012m and the reason why the strain 012m can establish a symbiotic relationship with G. elata in some extent from the perspective of genomics.