For the first time in more than half a century, a joint Cuban/American science team has worked together to quantify the impacts of chemical weathering and sustainable agriculture on river water quality in Cuba-the largest and most populous Caribbean island. Such data are critical as the world strives to meet sustainable development goals and for understanding rates of landscape change in the tropics, an understudied region. To characterize the landscape, we collected and analyzed water samples from 25 rivers in central Cuba where upstream land use varies from forested to agricultural. Cuban river waters bear the fingerprint of the diverse rock types underlying the island, and many carry exceptionally high dissolved loads. Chemical denudation rates are mostly among the top 25% globally and are similar to those measured in other Caribbean islands. High rates of solute export and the distinct composition of the waters in specific basins suggest flow paths that bring river source waters into contact with fresh, weatherable rock-unusual in a warm, wet, tropical climate where weathering should extend deep below the surface. Tectonically driven uplift likely maintains the supply of weatherable material, leading to channel incision and, thus, to the exposure of bedrock in many river channels. Despite centuries of agriculture, the impact on these rivers' biogeochemistry is limited. Although river water in many central Cuban rivers has high levels of E. coli bacteria, likely sourced from livestock, concentrations of dissolved nitrogen are far lower than other areas where intensive agriculture is practiced, such as the Mississippi River Basin. This suggests the benefits of Cuba's shift to conservation agriculture after 1990 and provides a model for more sustainable agriculture worldwide.

Cells exist in a state of continuous metabolic flux. The Krebs cycle, a central metabolic hub in the cell, is responsible for supplying precursors for the synthesis of amino acids, nucleotides, and compounds required for energy transfer. During periods of increased metabolic flux, metabolites in the Krebs cycle become depleted and must be replenished. Pyruvate carboxylase (PC), a multifunctional enzyme, replenishes the Krebs cycle by catalyzing the conversion of pyruvate to oxaloacetate, a Krebs cycle intermediate. The Shorewood SMART Team (Students Modeling A Research Topic) created a model of PC using 3D printing technology. PC contains four distinct domains: biotin carboxylase (BC), central allosteric, carboxyltransferase (CT), and biotin carboxyl carrier protein (BCCP). The overall reaction is initiated by BCCP‐biotin carboxylation in the BC domain. BCCP‐carboxybiotin physically translocates to the CT domain to transfer its carboxyl group to pyruvate. The active site of the CT domain undergoes a reconfiguration upon pyruvate binding to accommodate the docking of BCCP‐carboxybiotin for pyruvate carboxylation. With the rise in antibiotic resistance, understanding how PC functions may provide a target in developing new antibiotics, whereby the new drug would eliminate critical metabolic activity, thus killing the bacteria. Supported by a grant from the NIH‐CTSA UL1RR031973.

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