Urea assimilation and oxidation support activity of phylogenetically diverse microbial communities of the dark ocean.

Urea is hypothesized to be an important source of nitrogen and chemical energy to microorganisms in the deep sea; however, direct evidence for urea use below the epipelagic ocean is lacking. Here, we explore urea utilization from 50 to 4000 meters depth in the northeastern Pacific Ocean using metagenomics, nitrification rates, and single-cell stable-isotope-uptake measurements with nanoscale secondary ion mass spectrometry. We find that on average 25% of deep-sea cells assimilated urea-derived N (60% of detectably active cells), and that cell-specific nitrogen-incorporation rates from urea were higher than that from ammonium.

Microbial NO consumption in and above marine NO production hotspots.

The ocean is a net source of NO, a potent greenhouse gas and ozone-depleting agent. However, the removal of NO via microbial NO consumption is poorly constrained and rate measurements have been restricted to anoxic waters. Here we expand NO consumption measurements from anoxic zones to the sharp oxygen gradient above them, and experimentally determine kinetic parameters in both oxic and anoxic seawater for the first time.

Amperometric sensor for nanomolar nitrous oxide analysis.

Nitrous oxide is an important greenhouse gas and there is a need for sensitive techniques to study its distribution in the environment at concentrations near equilibrium with the atmosphere (9.6 nM in water at 20 °C). Here we present an electrochemical sensor that can quantify NO in the nanomolar range.

Dual nitrogen and oxygen isotope fractionation during anaerobic ammonium oxidation by anammox bacteria.

Natural abundance of stable nitrogen (N) and oxygen (O) isotopes are invaluable biogeochemical tracers for assessing the N transformations in the environment. To fully exploit these tracers, the N and O isotope effects (ε and ε) associated with the respective nitrogen transformation processes must be known. However, the N and O isotope effects of anaerobic ammonium oxidation (anammox), one of the major fixed N sinks and NO producers, are not well known.