Microbial processes regulating carbon cycling in ancient oceans remain poorly understood, yet characterizing these processes is critical for understanding early Earth biogeochemistry. Here, we investigate microbial communities associated with sinking particles regulating carbon cycling in meromictic Fayetteville Green Lake, a mid‐Proterozoic marginal ocean analog. The lake's photic zone spans oxic through sulfidic conditions,...

Introduction Assimilation of reduced nitrogen is less energetically costly than assimilation of oxidized forms. In the open ocean, ammonium is generally absent from the water column, including in oxygen-deficient zones (ODZs). Some microorganisms can use alternative organic reduced nitrogen forms like urea and cyanate, as indicated by the presence of cyanase ( cynS ) and urease ( ureC ) genes. Methods Here we examine the Hawai...

Marine snow and other particles are abundant in estuaries, where they drive biogeochemical transformations and elemental transport. Particles range in size, thereby providing a corresponding gradient of habitats for marine microorganisms. We used standard normalized amplicon sequencing, verified with microscopy, to characterize taxon‐specific microbial abundances, (cells per litre of water and per milligrams of particles), acr...

Domoic acid-producing blooms of the diatom genus Pseudo-nitzschia are pervasive in coastal environments globally. Domoic acid, a neurotoxin, accumulates via trophic transfer into marine food webs and is often associated with mass marine mammal mortality and stranding events. In Southern California, California sea lions ( Zalophus californianus ) are an indicator species for food web impacts of domoic acid because they are abun...

In lakes, seasonal phytoplankton blooms and allochthonous plant debris intensify particulate organic carbon fluxes to the lakebed. Microbes associated with these particles likely vary with organic substrate lability and redox conditions. To explore microbial compositional responses to these variables, we analyzed particle‐associated and free‐living assemblages in the permanently redox‐stratified Fayetteville Green Lake using 1...

Grazing by protists and viral infection are the main known sources of marine bacterial mortality, and both processes shape the structure and ecology of microbial communities. We diluted planktonic microbial communities to determine how decreasing the encounter rate between bacteria, grazers, and viruses affects community structure. In experimental treatments, sea water was diluted 10‐fold in water from which protists and bacte...

Marine microbes make up a key part of ocean food webs and drive ocean chemistry through a range of metabolic processes. A fundamental question in ecology is whether the diversity of organisms in a community shapes the ecological functions of that community. While there is substantial evidence to support a positive link between diversity and ecological productivity for macro‐organisms in terrestrial environments, this relations...