A Conductive 3D Dual-Metal π-d Conjugated Metal-Organic Framework Fe3 (HITP)2 /bpm@Co for Highly Efficient Oxygen Evolution Reaction.

Although 2D π-d conjugated metal-organic frameworks (MOFs) exhibit high in-plane conductivity, the closely stacked layers result in low specific surface area and difficulty in mass transfer and diffusion. Hence, a conductive 3D MOF Fe3 (HITP)2 /bpm@Co (HITP = 2,3,6,7,10,11-hexaiminotriphenylene) is reported through inserting bpm (4,4'-bipyrimidine) ligands and Co2+ into the interlayers of 2D MOF Fe3 (HITP)2 . Compared to 2D Fe3 (HITP)2 (37.23 m2  g-1 ), 3D Fe3 (HITP)2 /bpm@Co displays a huge improvement in the specific surface area (373.82 m2  g-1 ). Furthermore, the combined experimental and density functional theory (DFT) theoretical calculations demonstrate the metallic behavior of Fe3 (HITP)2 /bpm@Co, which will benefit to the electrocatalytic activity of it. Impressively, Fe3 (HITP)2 /bpm@Co exhibits prominent and stable oxygen evolution reaction (OER) performance (an overpotential of 299 mV vs RHE at a current density of 10 mA cm-2 and a Tafel slope of 37.14 mV dec-1 ), which is superior to 2D Fe3 (HITP)2 and comparable to commercial IrO2 . DFT theoretical calculation reveals that the combined action of the Fe and Co sites in Fe3 (HITP)2 /bpm@Co is responsible for the enhanced electrocatalytic activity. This work provides an alternative approach to develop conductive 3D MOFs as efficient electrocatalysts.

MvaT binds to the PexsC promoter to repress the type III secretion system in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an opportunistic human pathogen capable of causing a variety of acute and chronic infections. Its type III secretion system (T3SS) plays a critical role in pathogenesis during acute infection. ExsA is a master regulator that activates the expression of all T3SS genes. Transcription of exsA is driven by two distinct promoters, its own promoter PexsA and its operon promoter PexsC. Here, in combination with a DNA pull-down assay and mass spectrometric analysis, we found that a histone-like nucleoid-structuring (H-NS) family protein MvaT can bind to the PexsC promoter. Using EMSA and reporter assays, we further found that MvaT directly binds to the PexsC promoter to repress the expression of T3SS genes. The repression of MvaT on PexsC is independent of ExsA, with MvaT binding to the -429 to -380 bp region relative to the transcription start site of the exsC gene. The presented work further reveals the complex regulatory network of the T3SS in P. aeruginosa.

Lead-Free Perovskite Cs2 SnBr6 /rGO Composite for Photocatalytic Selective Oxidation of 5-Hydroxymethylfurfural to 2,5-Diformylfuran.

Severe poisonousness and prolonged instability existing in organic-inorganic lead-based perovskite are two matters seriously hindering its potential future application in photocatalysis. Therefore, it is particularly important to explore ecology-friendly, air-stable and highly active metal-halide perovskites. Herein, a new and stable lead-free perovskite Cs2 SnBr6 decorated with reduced graphene oxide (rGO), is synthesized and employed in the photocatalytic organic conversion. The as-prepared Cs2 SnBr6 is ultrastable, exhibiting no clear changes after being placed in the air for six months. The Cs2 SnBr6 /rGO composite shows excellent photocatalytic activity in photo-driven-oxidation of 5-hydroxymethylfurfural (HMF) to high value enclosed 2,5-diformylfuran (DFF), achieving>99.5 % conversion of HMF and 88 % DFF selectivity in the presence of green oxidant O2 . Comprehensive characterizations disclose a multistep reaction mechanism, demonstrating that the molecular oxygen, photogenerated carriers, ⋅O2 - and 1 O2 altogether synergistically participate in the effective photo-driven conversion of HMF to DFF. This work expands the material gallery towards selective organic conversion and environmentally friendly perovskite options for photocatalytic application.

Regulatory and structural mechanisms of PvrA-mediated regulation of the PQS quorum-sensing system and PHA biosynthesis in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is capable of causing acute and chronic infections in various host tissues, which depends on its abilities to effectively utilize host-derived nutrients and produce protein virulence factors and toxic compounds. However, the regulatory mechanisms that direct metabolic intermediates towards production of toxic compounds are poorly understood. We previously identified a regulatory protein PvrA that controls genes involved in fatty acid catabolism by binding to palmitoyl-coenzyme A (CoA). In this study, transcriptomic analyses revealed that PvrA activates the Pseudomonas quinolone signal (PQS) synthesis genes, while suppressing genes for production of polyhydroxyalkanoates (PHAs). When palmitic acid was the sole carbon source, mutation of pvrA reduced production of pyocyanin and rhamnolipids due to defective PQS synthesis, but increased PHA production. We further solved the co-crystal structure of PvrA with palmitoyl-CoA and identified palmitoyl-CoA-binding residues. By using pvrA mutants, we verified the roles of the key palmitoyl-CoA-binding residues in gene regulation in response to palmitic acid. Since the PQS signal molecules, rhamnolipids and PHA synthesis pathways are interconnected by common metabolic intermediates, our results revealed a regulatory mechanism that directs carbon flux from carbon/energy storage to virulence factor production, which might be crucial for the pathogenesis.

Reversion of Ceftazidime Resistance in Pseudomonas aeruginosa under Clinical Setting.

Pseudomonas aeruginosa is an important nosocomial pathogen which frequently becomes resistant to most antibiotics used in chemotherapy, resulting in treatment failure among infected individuals. Although the evolutionary trajectory and molecular mechanisms for becoming ß-lactam resistant have been well established for P. aeruginosa, the molecular basis of reversion from ß-lactam resistant to susceptible is largely unexplored. In this study, we investigated the molecular mechanisms by which a ceftazidime-resistant clinical strain is converted to a ceftazidime-susceptible isolate under the clinical setting. RNA sequencing and genomic DNA reference mapping were conducted to compare the transcriptional profiles and chromosomal mutations between these two isolates. Our results demonstrate that a gain-of-function mutation in ampD, via deletion of a 53 bp duplicated nucleotide sequence, is the contributory factor for the conversion. Furthermore, we show for the first time that AmpD is involved in intraspecies competitiveness in P. aeruginosa. We also found that AmpD is not responsible for phenotypic changes between R1 and S2, including growth rate, motilities, pyocyanin, rhamnolipid, and biofilm production. This finding provides novel insights into the alteration of ß-lactam sensitivity in P. aeruginosa under the clinical setting.

Spatiotemporal Dynamics of Carbon Footprint of Main Crop Production in China.

As a major agricultural country, the comprehensive accounting of the dynamics and composition of the carbon footprint of major crops in China will provide a decision-making basis for environmental management and agricultural green development in the whole process of the major crop production system in China. To investigate the spatiotemporal dynamics of the carbon footprint for major crops in China, a life cycle-based carbon footprint approach was used to evaluate the carbon footprint per unit area (CFA) and per unit yield (CFY) of eight crops for the period of 1990 to 2019. Our results showed that the CFA for all major crops showed an increasing trend with time before 2016 but slowly decreased afterward, while the CFY decreased by 16-43% over the past 30 years due to the increase in crop yield. The three main grain crops, rice (4871 ± 418 kg CO2-eq · ha-1), wheat (2766 ± 552 kg CO2-eq · ha-1), and maize (2439 ± 530 kg CO2-eq · ha-1), showed the highest carbon footprint and contribution to the total greenhouse gas (GHG) emissions, mainly due to their larger cultivated areas and higher fertilizer application rates. CH4 emission was the major component of the carbon footprint for rice production, accounting for 66% and 48% of the CFA and CFY, respectively, while fertilizer production and usage were the largest components of carbon footprint for dryland crops, making up to 26-49% of the CFA and 26-50% of the CFY for different crops. The present study also highlighted the spatial and temporal patterns of the carbon footprint for major crops in China, which could serve as references for the development of best management practices for different crop production in China, to mitigate agricultural GHG emission and to pursue low-carbon agriculture.

Emergence and Transfer of Plasmid-Harbored rmtB in a Clinical Multidrug-Resistant Pseudomonas aeruginosa Strain.

Multidrug-resistant (MDR) Pseudomonas aeruginosa poses a great challenge to clinical treatment. In this study, we characterized a ST768 MDR P. aeruginosa strain, Pa150, that was isolated from a diabetic foot patient. The minimum inhibitory concentration (MIC) assay showed that Pa150 was resistant to almost all kinds of antibiotics, especially aminoglycosides. Whole genome sequencing revealed multiple antibiotic resistant genes on the chromosome and a 437-Kb plasmid (named pTJPa150) that harbors conjugation-related genes. A conjugation assay verified its self-transmissibility. On the pTJPa150 plasmid, we identified a 16S rRNA methylase gene, rmtB, that is flanked by mobile genetic elements (MGEs). The transfer of the pTJPa150 plasmid or the cloning of the rmtB gene into the reference strain, PAO1, significantly increased the bacterial resistance to aminoglycoside antibiotics. To the best of our knowledge, this is the first report of an rmtB-carrying conjugative plasmid isolated from P. aeruginosa, revealing a novel possible transmission mechanism of the rmtB gene.

Acetylation of CspC Controls the Las Quorum-Sensing System through Translational Regulation of rsaL in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a ubiquitous pathogenic bacterium that can adapt to a variety environments. The ability to effectively sense and respond to host local nutrients is critical for the infection of P. aeruginosa. However, the mechanisms employed by the bacterium to respond to nutrients remain to be explored. CspA family proteins are RNA binding proteins that are involved in gene regulation. We previously demonstrated that the P. aeruginosa CspA family protein CspC regulates the type III secretion system in response to temperature shift. In this study, we found that CspC regulates the quorum-sensing (QS) systems by repressing the translation of a QS negative regulatory gene, rsaL. Through RNA immunoprecipitation coupled with real-time quantitative reverse transcription-PCR (RIP-qRT-PCR) and electrophoretic mobility shift assays (EMSAs), we found that CspC binds to the 5' untranslated region of the rsaL mRNA. Unlike glucose, itaconate (a metabolite generated by macrophages during infection) reduces the acetylation of CspC, which increases the affinity between CspC and the rsaL mRNA, leading to upregulation of the QS systems. Our results revealed a novel regulatory mechanism of the QS systems in response to a host-generated metabolite. IMPORTANCE Bacterial infectious diseases impose a severe threat to human health. The ability to orchestrate virulence determinant in response to the host environment is critical for the pathogenesis of bacterial pathogens. Pseudomonas aeruginosa is a leading pathogen that causes various infections in humans. In P. aeruginosa, the quorum-sensing (QS) systems play an important role in regulating the production of virulence factors. In this study, we find that a small RNA binding protein, CspC, regulates the QS systems by repressing the expression of a QS negative regulator. We further demonstrate that CspC is acetylated in response to a host-derived metabolite, itaconate, which alters the function of CspC in regulating the QS system. The importance of this work is in elucidation of a novel regulatory pathway that regulates virulence determinants in P. aeruginosa in response to a host signal.

NrtR Mediated Regulation of H1-T6SS in Pseudomonas aeruginosa.

NrtR is a Nudix-related transcriptional regulator that is distributed among diverse bacteria and plays an important role in modulating bacterial intracellular NAD homeostasis. Previously, we showed that NrtR influences the T3SS expression and pathogenesis of Pseudomonas aeruginosa and demonstrated that NrtR mediates T3SS regulation through the cAMP/Vfr pathway. In the present study, we found that mutation of the nrtR gene leads to upregulation of the Hcp secretion island-I type VI secretion system (H1-T6SS). Further analysis revealed that mutation of the nrtR gene results in upregulation of regulatory RNAs (RsmY/RsmZ) that are known to control the H1-T6SS by sequestration of RsmA or RsmN. Simultaneous deletion of rsmY/rsmZ reduced the expression of H1-T6SS in the ΔnrtR mutant. In addition, overexpression of either rsmA or rsmN in ΔnrtR decreased H1-T6SS expression. Chromatin immunoprecipitation (ChIP)-Seq and electrophoretic mobility shift assay (EMSA) analyses revealed that NrtR directly binds to the promoters of rsmY, rsmZ and tssA1 (first gene of the H1-T6SS operon). Overall, the results from this study reveal the molecular details of NrtR-mediated regulation of H1-T6SS in P. aeruginosa. IMPORTANCE NrtR is a Nudix-related transcriptional regulator and controls the NAD cofactor biosynthesis in bacteria. P. aeruginosa NrtR binds to the intergenic region between nadD2 and pcnA to repress the expression of the two operons, therefore controlling the NAD biosynthesis. We have previously reported that NrtR controls T3SS expression via the cAMP/Vfr pathway in P. aeruginosa. However, the global regulatory function and direct binding targets of the NrtR remain elusive in P. aeruginosa. This study reveals novel direct regulatory targets of the NrtR in P. aeruginosa, elucidating the molecular mechanism of NrtR-mediated regulation of H1-T6SS.

RplI interacts with 5' UTR of exsA to repress its translation and type III secretion system in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is an important opportunistic pathogen capable of causing variety of infections in humans. The type III secretion system (T3SS) is a critical virulence determinant of P. aeruginosa in the host infections. Expression of the T3SS is regulated by ExsA, a master regulator that activates the expression of all known T3SS genes. Expression of the exsA gene is controlled at both transcriptional and posttranscriptional levels. Here, we screened a P. aeruginosa transposon (Tn5) insertional mutant library and found rplI, a gene coding for the ribosomal large subunit protein L9, to be a repressor for the T3SS gene expression. Combining real-time quantitative PCR (qPCR), western blotting and lacZ fusion assays, we show that RplI controls the expression of exsA at the posttranscriptional level. Further genetic experiments demonstrated that RplI mediated control of the exsA translation involves 5' untranslated region (5' UTR). A ribosome immunoprecipitation assay and qPCR revealed higher amounts of a 24 nt fragment from exsA mRNA being associated with ribosomes in the ΔrplI mutant. An interaction between RplI and exsA mRNA harboring its 24 nt, but not 12 nt, 5' UTR was confirmed by RNA Gel Mobility Shift and Microscale Thermophoresis assays. Overall, this study identifies the ribosomal large subunit protein L9 as a novel T3SS repressor that inhibits ExsA translation in P. aeruginosa.

Parallel Evolution to Elucidate the Contributions of PA0625 and parE to Ciprofloxacin Sensitivity in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a ubiquitous pathogen that causes a wide range of acute and chronic infections. Ciprofloxacin, one of the first-line fluoroquinolone class antibiotics, is commonly used for the treatment of P. aeruginosa infections. However, ciprofloxacin-resistant P. aeruginosa is increasingly reported worldwide, making treatment difficult. To determine resistance-related mutations, we conducted an experimental evolution using a previously identified ciprofloxacin-resistant P. aeruginosa clinical isolate, CRP42. The evolved mutants could tolerate a 512-fold higher concentration of ciprofloxacin than CRP42. Genomic DNA reference mapping was performed, which revealed mutations in genes known to be associated with ciprofloxacin resistance as well as in those not previously linked to ciprofloxacin resistance, including the ParER586W substitution and PA0625 frameshift insertion. Simulation of the ParER586W substitution and PA0625 frameshift insertion by gene editing in CRP42 and the model strain PAO1 demonstrated that while the PA0625 mutation does contribute to resistance, mutation in the ParER586W does not contribute to resistance but rather affects tolerance against ciprofloxacin. These findings advance our understanding of ciprofloxacin resistance in P. aeruginosa.

Molecular spectra of a D-π-A typed polydentate ligand chromophore and its simultaneous response to trace Cu2+ and Co2.

A D-π-A conjugated polydentate ligand chromophore, N-8'-quinolyl-2,4,6- trihydroxyl benzamide (NQTB), was identified and synthesized using tri-hydroxyl phenol as donated-electron group, N-heterocycle quinoline as accepted-electron one and CN bond as bridged one. It was expected to chelate some heavy metal ions with prominent colorimetric or spectral changes. After its UV-vis absorption spectrum was investigated in detail, it was noted that NQTB possessed excellent spectral recognition ability to Cu2+ and Co2+ from other coexisting ions in aqueous. Under the optimized conditions, NQTB could simultaneously discriminate trace Cu2+ and Co2+ in environmental aqueous samples with low detection limits (1.9 × 10-8 mol/L and 5.7 × 10-8 mol/L) and satisfying analytical precisions (R.S.D. ≤3.3% and ≤2.6%) respectively. The sensing mechanism was confirmed to form some stable 5-membered-co-6-membered condensed rings between Cu2+/Co2+ and O/N atoms in NQTB.