Experiments and modelling unravel mechanisms of nitrous oxide production from nitrate, the primary nitrous oxide production pathway in oxygen minimum zones. Results highlight the critical role of microbial interactions in regulating this pathway.

Glycolate is a major product of phytoplankton photorespiration, but its fate in the microbial food web is not well constrained. Here, we used stable isotope probing and mass spectrometry combined with genomic analyses and microscopy to quantify glycolate metabolism by a taxonomically diverse set of heterotrophic marine bacteria. We found that 9 of 16 tested strains with the genomic capability to metabolize glycolate directly assimilated and respired glycolate carbon in monoculture. We next co-cultivated glycolate-incorporating strains with non-incorporating strains and found that several cross-feeders incorporated more glycolate carbon into their biomass than direct incorporators. Carbon use efficiency, reflecting proportional differences in movement of glycolate carbon into biomass versus into carbon dioxide, were distinct across cocultures and ranged from 0.01 - 3.15% depending on the strain mixtures. These results suggest that the fate of glycolate carbon is not limited to microbial taxa with the genetic capability for direct assimilation, and that bacterial metabolic interactions via cross-feeding play a critical role in influencing the efficiency of carbon transfer. Such information is critical to refine conceptual and numerical models of heterotrophic processing and transfer of organic carbon in an era of global change with predicted increases in photorespiration. ### Competing Interest Statement The authors have declared no competing interest. Lawrence Livermore National Laboratory, https://ror.org/041nk4h53, 19-LW-044

Nitrite oxidation, the second step of nitrification, is essential to the global nitrogen cycle. Nitrite-oxidizing bacteria (NOB) are classified into two groups based on the cellular localization of th...

A new study led by Barbara Bayer (CeMESS, University of Vienna) discovered that ammonia-oxidizing microorganisms contribute much less to carbon fixation in the ocean than previously assumed. The study...