Size-fraction partitioning of community gene transcription and rates of nitrogen metabolism in a marine oxygen minimum zone

The taxonomic composition and functional potential of marine microbial communities can vary at the microscale between particle-associated (PA; >1.6 µm) and free-living (FL; 0.2-1.6 µm) niches. It remains unclear, however, how the expression and activity of most biochemical processes differ between PA and FL fractions. We combined metatranscriptomics with rate measurements to compare microbial activity across PA and FL fractions in the major oxygen minimum zone (OMZ) of the Eastern Tropical North Pacific, focusing on key metabolic processes of the dissimilatory nitrogen (N) cycle.