Functional Genomics Reveals Synthetic Lethality between Phosphogluconate Dehydrogenase and Oxidative Phosphorylation

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Ecosystem-Scale Oxygen Manipulations Alter Terminal Electron Acceptor Pathways in a Eutrophic Reservoir

Lakes and reservoirs globally are experiencing unprecedented changes in land use and climate, depleting dissolved oxygen (DO) in the bottom waters (hypolimnia) of these ecosystems. Because DO is the most energetically favorable terminal electron acceptor (TEA) for organic carbon mineralization, its availability controls the onset of alternate TEA pathways (for example, denitrification, manganese reduction, iron reduction, sulfate reduction, methanogenesis). Low DO concentrations can trigger organic carbon mineralization via alternate TEA pathways in the water column and sediments, which has important implications for greenhouse gas production [carbon dioxide (CO₂) and methane (CH₄)]. In this study, we experimentally injected supersaturated DO into the hypolimnion of a eutrophic reservoir and measured concentrations of TEAs and terminal electron products (TEPs) in the experimental reservoir and an upstream reference reservoir. We calculated the electron equivalents yielded from each TEA pathway and estimated the contributions of each TEA pathway to organic carbon processing in both reservoirs. DO additions to the hypolimnion of the experimental reservoir promoted aerobic respiration, suppressing most alternate TEA pathways and resulting in elevated CO₂ accumulation. In comparison, organic carbon mineralization in the reference reservoir’s anoxic hypolimnion was dominated by alternate TEA pathways, resulting in both CH₄ and CO₂ accumulation. Our ecosystem-scale experiments demonstrate that the alternate TEA pathways that succeed aerobic respiration in lakes and reservoirs can be manipulated at the ecosystem scale. Moreover, changes in the DO dynamics of freshwater lakes and reservoirs may result in concomitant changes in the redox reactions in the water column that control organic carbon mineralization and greenhouse gas accumulation.

     

Cage location effects on visitor attendance at three Sacramento Zoo mangabey enclosures

Research on the effects of enrichment would do well to consider carefully location and/or visitor habituation effects on animal behavior. In the present series of studies, 19,847 visitors to the Sacramento Zoo were counted and categorized by age and sex as they appeared at each of three mangabey cages having only slightly different locations within the zoo. A cage nearest the exit/entrance received significantly more visitors (had greater attracting power) than did a cage away from the exit but on the main path, while the latter cage had more patronage than a cage that was only a few feet off the main walkway. These effects persisted through both subtle and complete changes in the animal inhabitants of the cages. These very strong effects, which are similar to those described by Melton's (Pychological Bulletin 30:720, 721, 1983; Museum News 14(3):6–8, 1936) classic “exit gradient” as well as to other possible effects of simple location (e.g., visitor habituation) are particularly important for species that are behaviorally responsive to visitors.