Abstract
Phytoplankton and associated microbial communities provide organic carbon to oceanic food webs and drive ecosystem dynamics. However, capturing those dynamics is challenging. Here, an in situ, semi-Lagrangian, robotic sampler profiled pelagic microbes at 4 h intervals over ~2.6 days in North Pacific high-nutrient, low-chlorophyll waters. We report on the community structure and transcriptional dynamics of microbes in an operationally large size class (>5 μm) predominantly populated by dinoflagellates, ciliates, haptophytes, pelagophytes, diatoms, cyanobacteria (chiefly Synechococcus), prasinophytes (chiefly Ostreococcus), fungi, archaea, and proteobacteria. Apart from fungi and archaea, all groups exhibited 24-h periodicity in some transcripts, but larger portions of the transcriptome oscillated in phototrophs. Periodic photosynthesis-related transcripts exhibited a temporal cascade across the morning hours, conserved across diverse phototrophic lineages. Pronounced silica:nitrate drawdown, a high flavodoxin to ferredoxin transcript ratio, and elevated expression of other Fe-stress markers indicated Fe-limitation. Fe-stress markers peaked during a photoperiodically adaptive time window that could modulate phytoplankton response to seasonal Fe-limitation. Remarkably, we observed viruses that infect the majority of abundant taxa, often with total transcriptional activity synchronized with putative hosts. Taken together, these data reveal a microbial plankton community that is shaped by recycled production and tightly controlled by Fe-limitation and viral activity.
Highlights
Phytoplankton productivity is essential for supporting marine food webs and represents a key variable in Supplementary information The online version of this article contains supplementary material, which is available to authorized users.biogeochemical cycling and climate models [1]
Phytoplankton [4,5,6,7,8], they cannot capture ecological interactions with uncultured community members or the influence of the advection dynamics found in nature
Despite sustaining highly productive fisheries, this region is characterized by frequent, variable levels of iron stress (Fe
Summary
A comparison of drifts from diverse environments revealed a daily “cascade” of transcriptional activity across taxa that was conserved on ocean basin scales [13]. It is unknown whether these findings extend to the majority of eukaryotic primary producers (diatoms, haptophytes, pelagophytes, chlorophytes, etc.), planktonic predators such as ciliates and dinoflagellates, and particleassociated microbes. The Weighted Gene Correlation Network Analysis (WGCNA) R package [18] was used as previously described [13] to identify modules of conserved expression among ORFs and functional clusters
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