Metaproteomics reveal that rapid perturbations in organic matter prioritize functional restructuring over taxonomy in western Arctic Ocean microbiomes

We examined metaproteome profiles from two Arctic microbiomes during 10-day shipboard incubations to directly track
early functional and taxonomic responses to a simulated algal bloom and an oligotrophic control. Using a novel peptidebased enrichment analysis, significant changes (p-value < 0.01) in biological and molecular functions associated with carbon
and nitrogen recycling were observed. Within the first day under both organic matter conditions, Bering Strait surface
microbiomes increased protein synthesis, carbohydrate degradation, and cellular redox processes while decreasing C1
metabolism. Taxonomic assignments revealed that the core microbiome collectively responded to algal substrates by
assimilating carbon before select taxa utilize and metabolize nitrogen intracellularly. Incubations of Chukchi Sea bottom
water microbiomes showed similar, but delayed functional responses to identical treatments. Although 24 functional terms
were shared between experimental treatments, the timing, and degree of the remaining responses were highly variable,
showing that organic matter perturbation directs community functionality prior to alterations to the taxonomic distribution at
the microbiome class level. The dynamic responses of these two oceanic microbial communities have important implications
for timing and magnitude of responses to organic perturbations within the Arctic Ocean and how community-level functions
may forecast biogeochemical gradients in oceans.