Nitrate Reduction Functional Genes and Nitrate Reduction Potentials Persist in Deeper Estuarine Sediments. Why?

Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are processes occurring simultaneously under oxygen-limited or anaerobic conditions, where both compete for nitrate and organic carbon. Despite their ecological importance, there has been little investigation of how denitrification and DNRA potentials and related functional genes vary vertically with sediment depth. Nitrate reduction potentials measured in sediment depth profiles along the Colne estuary were in the upper range of nitrate reduction rates reported from other sediments and showed the existence of strong decreasing trends both with increasing depth and along the estuary. Denitrification potential decreased along the estuary, decreasing more rapidly with depth towards the estuary mouth. In contrast, DNRA potential increased along the estuary. Significant decreases in copy numbers of 16S rRNA and nitrate reducing genes were observed along the estuary and from surface to deeper sediments. Both metabolic potentials and functional genes persisted at sediment depths where porewater nitrate was absent. Transport of nitrate by bioturbation, based on macrofauna distributions, could only account for the upper 10 cm depth of sediment. A several fold higher combined freeze-lysable KCl-extractable nitrate pool compared to porewater nitrate was detected. We hypothesised that his could be attributed to intracellular nitrate pools from nitrate accumulating microorganisms like Thioploca or Beggiatoa. However, pyrosequencing analysis did not detect any such organisms, leaving other bacteria, microbenthic algae, or foraminiferans which have also been shown to accumulate nitrate, as possible candidates. The importance and bioavailability of a KCl-extractable nitrate sediment pool remains to be tested. The significant variation in the vertical pattern and abundance of the various nitrate reducing genes phylotypes reasonably suggests differences in their activity throughout the sediment column. This raises interesting questions as to what the alternative metabolic roles for the various nitrate reductases could be, analogous to the alternative metabolic roles found for nitrite reductases

The animal welfare aspects of surgical artificial insemination in the canine

Letter to the Edito

The animal welfare aspects of surgical artificial insemination in the canine

[Extract] Dear Editor As a group of veterinarians with a particular interest, and postgraduate specialist qualifications, in veterinary reproduction (theriogenology), we are writing to our colleagues in the profession to consider the ethics and welfare of surgical artificial insemination in the canine

Unraveling the Anomalous Solvatochromic Response of the Formate Ion Vibrational Spectrum: An Infrared, Ar-Tagging Study of the HCO2-, DCO2-, and HCO2-center dot H2O Ions

Reductive activation offers an attractive synthetic route for conversion of CO2 to transportable fuels, a process that often involves creation of the formate ion as an intermediate. We carry out an Ar-tagging infrared spectroscopic study of isolated HCO2¯ and its first hydrate, HCO2¯·H2O, and analyze the resulting band patterns with electronic structure and vibrationally anharmonic calculations. Strong vibronic interactions and intramolecular mode couplings are identified that are responsible for the deceptively complex solvation behavior of this familiar ion. In particular, the CH stretch fundamental is found to be anomalously low in energy in the isolated ion and to dramatically blue shift (by hundreds of cm–1) upon solvation. These two effects are traced to the large dependence of the electronic wave function on the CH bond length, reminiscent of the classic curve-crossings that dominate the dissociation behavior of neutral salt molecules