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This paper presents a study of designing phase-specific and -mixed Ir−Ru−Mn trimetallic electrocatalysts with enhanced performance. By changing the content of Ru, the alloy electrocatalyst evolved from a face-centered tetragonal (fct) phase to a mixture of fct and hexagonal close-packed (hcp) phases and finally to the hcp phase. Among these trimetallic systems, the hcp-phase Ir0.23Ru0.20Mn0.57 electrocatalyst (Ru/Ir = 0.47:0.53) delivered the best performance toward the oxygen evolution reaction (OER), achieving an overpotential of 226 mV at 10 mA cm−2 and a Tafel slope of ∼46.8 mV dec−1. Interestingly, this low-Ir hcp-phase catalyst maintained stable operation for >57 h at a current density of 100 mA cm−2 in 0.1 M HClO4, whereas the Ir-rich fct-phase counterpart (Ir0.35Ru0.07Mn0.58) degraded within 22 h under identical conditions. Potentiodynamic polarization curve study indicated that oxidative dissolution is the dominant degradation pathway, and the structural characterizations indicated that the hcp-phase alloy remained intact, while rutile-type IrRuMnOx oxide was formed for the fct-phase alloy electrocatalyst. These results underscore the effect of the crystal phase on OER durability of the electrocatalyst and point to a design strategy for improving the durability of OER electrocatalysts without increasing the Ir content. 

Abstract Heterologous expression of polyketide synthase (PKS) genes inEscherichia colihas enabled the production of various valuable natural and synthetic products. However, the limited availability of malonyl-CoA (M-CoA) inE. coliremains a substantial impediment to high-titer polyketide production. Here we address this limitation by disrupting the native M-CoA biosynthetic pathway and introducing an orthogonal pathway comprising a malonate transporter and M-CoA ligase, enabling efficient M-CoA biosynthesis under malonate supplementation. This approach substantially increases M-CoA levels, enhancing fatty acid and polyketide titers while reducing the promiscuous activity of PKSs toward undesired acyl-CoA substrates. Subsequent adaptive laboratory evolution of these strains provides insights into M-CoA regulation and identifies mutations that further boost M-CoA and polyketide production. This strategy improvesE. colias a host for polyketide biosynthesis and advances understanding of M-CoA metabolism in microbial systems. 

Abstract Anthropogenic perturbations to the nitrogen cycle, primarily through use of synthetic fertilizers, is driving an unprecedented increase in the emission of nitrous oxide (N2O), a potent greenhouse gas and an ozone depleting substance, causing urgency in identifying the sources and sinks of N2O. Microbial denitrification is a primary contributor to biotic production of N2O in anoxic regions of soil, marine systems, and wastewater treatment facilities. Here, through comprehensive genome analysis, we show that pathway partitioning is a ubiquitous mechanism of complete denitrification within microbial communities. We have investigated mechanisms and consequences of process partitioning of denitrification through detailed physiological characterization and kinetic modeling of a synthetic community of Rhodanobacter thiooxydans FW510-R12 and Acidovorax sp. GW101-3H11. We have discovered that these two bacterial isolates, from a heavily nitrate (NO3−) contaminated superfund site, complete denitrification through the exchange of nitrite (NO2−) and nitric oxide (NO). The process partitioning of denitrification and other processes, including amino acid metabolism, contribute to increased cooperativity within this denitrifying community. We demonstrate that certain contexts, such as high NO3−, cause unbalanced growth of community members, due to differences in their substrate utilization kinetics. The altered growth characteristics of community members drives accumulation of toxic NO2−, which disrupts denitrification causing N2O off gassing.