Bacterioplankton metabolism of phytoplankton lysates across a cyclone‐anticyclone eddy dipole impacts the cycling of semi‐labile organic matter in the photic zone

Abstract

Mesoscale eddies, prominent physical processes in the stratified ocean gyres, affect community composition and metabolic rates of both phytoplankton and heterotrophic bacterioplankton (free-living bacterial and archaeal) communities. We hypothesized that in situ differences in organic matter production would predispose bacterioplankton communities from cyclonic vs. anticyclonic eddies toward metabolic capabilities better suited to utilizing dissolved organic matter (DOM) from the phytoplankton groups commonly associated with each eddy polarity. To test this, we established dilution batch-culture bioassay incubations along a cyclone to anticyclone spatial transect in the North Pacific Subtropical Gyre. Unamended incubations, to assess spatial variability in ambient DOM bioavailability, and incubations amended with lysates of phytoplankton cultures were established and community growth and metabolic responses were assessed. Over timescales of days, lysate type was more influential than incubation origin: Prochlorococcus lysate was rapidly remineralized, while Emiliania huxleyi lysate was efficiently incorporated into biomass and developed a unique community of copiotrophic bacteria. Over timescales of 1 week to 1 month, eddy effects were indirectly apparent in their potential to promote metabolic processes related to DOM production and consumption. Surface lysate incubations showed priming of ambient DOM, that is, the remineralization of DOM, which was otherwise not bioavailable, in the presence of labile substrates. Some incubations originating from the deep chlorophyll maximum demonstrated signatures of chemoautotrophy fueled by nitrification, coincident with eddy-driven isopycnal uplift. We conclude that eddy polarity itself does not determine community-level bacterioplankton metabolic capabilities; however, mesoscale processes may indirectly affect slower, semi-labile organic matter processing in the oligotrophic ocean.

Deep ocean microbial communities produce more stable dissolved organic matter through the succession of rare prokaryotes

“…Furthermore, deep mesoscales eddies may have a similar effect of mixing differential microbial communities to unseen DOM. Eddies have been shown to contribute to shaping microbial communities and metabolism in the surface ocean ( 62 , 63 ) and influencing major ocean biogeochemical cycles ( 64 ). Our results support both phenomena.…”

Eddy-enhanced primary production sustains heterotrophic microbial activities in the Eastern Tropical North Atlantic

“…Lasternas et al, 2013;Rao et al, 2021) and DOM quality (e.g. Wear et al, 2020). DOM quality impacts bacterial biomass production (BP), bacterial respiration (BR), and bacterial growth efficiency (BGE; e.g.…”

The Seasonal Flux and Fate of Dissolved Organic Carbon Through Bacterioplankton in the Western North Atlantic

“…Both a filtered DOC sample and a TOC sample were collected to monitor changes in organic carbon over the course of each experiment. TOC samples were corrected by the contribution of BOC at T 0 and T Stationary , hereafter referred to as DOC * (Stephens et al, 2020;Wear et al, 2020). BA was observed to fall to low densities by T End (Supplementary Figure 1), so we considered TOC and DOC to be interchangeable by T End .…”