ABSTRACT
High catalytic activity, long-term stability, and economical Pt-free catalysts for the hydrogen evolution reaction (HER) are required for the conversion of renewable energy systems. Noble nanomaterial Pt is a superior electrolysis catalyst for water splitting under typical experimental conditions with a relatively low overpotential. However, the use of Pt is limited by its high cost and activity degradation over time. Among several prospective alternatives, Ru has emerged as a promising alkaline electrolysis catalyst because of its significant catalytic activity and reduced cost compared to Pt. We designed and suggested Pd-doped hollow Ru-Te nanorods (PdRuTeNRs) via successive galvanic replacement reactions of sacrificial Te nanotemplates to further boost efficiency. The Pd/partially oxidized RuO2/Ru/Te hetero-interfaced composition exhibited an HER mass activity of 11.3 A g-1 Ru, twice that of Pt. In addition, the present PdRuTeNRs sufficiently maintained the activity from the 2000-cycle continuous test, greatly reducing the required cost by a quarter.
ABSTRACT
Pyruvate is an important intermediate of central carbon metabolism and connects a variety of metabolic pathways in Escherichia coli Although the intracellular pyruvate concentration is dynamically altered and tightly balanced during cell growth, the pyruvate transport system remains unclear. Here, we identified a pyruvate transporter in E. coli using high-throughput transposon sequencing. The transposon mutant library (a total of 5 × 105 mutants) was serially grown with a toxic pyruvate analog (3-fluoropyruvate [3FP]) to enrich for transposon mutants lacking pyruvate transport function. A total of 52 candidates were selected on the basis of a stringent enrichment level of transposon insertion frequency in response to 3FP treatment. Subsequently, their pyruvate transporter function was examined by conventional functional assays, such as those measuring growth inhibition by the toxic pyruvate analog and pyruvate uptake activity. The pyruvate transporter system comprises CstA and YbdD, which are known as a peptide transporter and a conserved protein, respectively, whose functions are associated with carbon starvation conditions. In addition to the presence of more than one endogenous pyruvate importer, it has been suggested that the E. coli genome encodes constitutive and inducible pyruvate transporters. Our results demonstrated that CstA and YbdD comprise the constitutive pyruvate transporter system in E. coli, which is consistent with the tentative genomic locus previously suggested and the functional relationship with the extracellular pyruvate sensing system. The identification of this pyruvate transporter system provides valuable genetic information for understanding the complex process of pyruvate metabolism in E. coliIMPORTANCE Pyruvate is an important metabolite as a central node in bacterial metabolism, and its intracellular levels are tightly regulated to maintain its functional roles in highly interconnected metabolic pathways. However, an understanding of the mechanism of how bacterial cells excrete and transport pyruvate remains elusive. Using high-throughput transposon sequencing followed by pyruvate uptake activity testing of the selected candidate genes, we found that a pyruvate transporter system comprising CstA and YbdD, currently annotated as a peptide transporter and a conserved protein, respectively, constitutively transports pyruvate. The identification of the physiological role of the pyruvate transporter system provides valuable genetic information for understanding the complex pyruvate metabolism in Escherichia coli.
