Although edaphic antibiotic resistance genes (ARGs) pose serious threats to human well-being, their spatially explicit patterns and responses to environmental constraints at the global scale are not well understood. This knowledge gap is hindering the global action plan on antibiotic resistance launched by the World Health Organization. Here, a global analysis of 1088 soil metagenomic samples detected 558 ARGs in soils, where ARG abundance in agricultural habitats was higher than that in nonagricultural habitats. Soil ARGs were mostly carried by clinical pathogens and gut microbes that mediated the control of climatic and anthropogenic factors to ARGs. We generated a global map of soil ARG abundance, where the identified microbial hosts, agricultural activities, and anthropogenic factors explained ARG hot spots in India, East Asia, Western Europe, and the United States. Our results highlight health threats from soil clinical pathogens carrying ARGs and determine regions prioritized to control soil antibiotic resistance worldwide.
21 September 2015 in Environmental Science & Technology
Dissimilatory nitrate reduction processes, including denitrification, anaerobic ammonium oxidation (ANAMMOX), and dissimilatory nitrate reduction to ammonium (DNRA), play an important role in controlling the nitrate dynamics and fate in estuarine and coastal environments. We investigated potential rates of denitrification, ANAMMOX, and DNRA in the sediments of the Yangtze Estuary via slurry incubation experiments combined with isotope‐tracing techniques to reveal their respective contributions to total nitrate reduction in this hypereutrophic estuarine ecosystem. Measured rates of denitrification, ANAMMOX, and DNRA ranged from 0.06 to 4.51 µmol N kg−1 h−1, 0.01 to 0.52 µmol N kg−1 h−1, and 0.03 to 0.89 µmol N kg−1 h−1, respectively. These potential dissimilatory nitrate reduction process rates correlated significantly with salinity, sulfide, organic carbon, and nitrogen. Denitrification contributed 38–96% total nitrate reduction in the Yangtze Estuary, as compared to 3–45% for DNRA and 1–36% for ANAMMOX. In total, the denitrification and ANAMMOX processes removed approximately 25% of the external inorganic nitrogen transported annually into the estuary. In contrast, most external inorganic nitrogen was retained in the estuary and contributes substantially to the severe eutrophication of the Yangtze Estuary.
Climate models project that extreme precipitation events will intensify in proportion to their intensity during the 21st century at large spatial scales. The identification of the causes of this phenomenon nevertheless remains tenuous. Using a large ensemble of North American regional climate simulations, we show that the more rapid intensification of more extreme events also appears as a robust feature at finer regional scales. The larger increases in more extreme events than in less extreme events are found to be primarily due to atmospheric circulation changes. Thermodynamically induced changes have relatively uniform effects across extreme events and regions. In contrast, circulation changes weaken moderate events over western interior regions of North America, and enhance them elsewhere. The weakening effect decreases and even reverses for more extreme events, whereas there is further intensification over other parts of North America, creating an “intense gets intenser” pattern over most of the continent.