Single-cell analysis reveals an active and heterotrophic microbiome in the Guaymas Basin deep subsurface with significant inorganic carbon fixation by heterotrophs.

Unlabelled: The marine subsurface is a long-term sink of atmospheric carbon dioxide with significant implications for climate on geologic timescales. Subsurface microbial cells can either enhance or reduce carbon sequestration in the subsurface, depending on their metabolic lifestyle. However, the activity of subsurface microbes is rarely measured.

Inactive hydrothermal vent microbial communities are important contributors to deep ocean primary productivity.

Active hydrothermal vents are oases for productivity in the deep ocean, but the flow of dissolved substrates that fuel such abundant life ultimately ceases, leaving behind inactive mineral deposits. The rates of microbial activity on these deposits are largely unconstrained. Here we show primary production occurs on inactive hydrothermal deposits and quantify its contribution to new organic carbon production in the deep ocean.

Rates and physicochemical drivers of microbial anabolic activity in deep-sea sediments and implications for deep time.

Sediment microorganisms influence global climate and redox by altering rates of organic carbon burial. However, the activity and ecology of benthic microorganisms are poorly characterized, especially in the deep sea. Here, we conducted nearly 300 stable isotope tracer experiments in sediments from the Pacific and Atlantic oceans (100-4500 m water depth) to determine the rates, spatial distribution, and physicochemical controls on microbial total anabolic activity, nitrogen fixation, and inorganic/organic carbon uptake.

NanoSIMS sample preparation decreases isotope enrichment: magnitude, variability and implications for single-cell rates of microbial activity.

The activity of individual microorganisms can be measured within environmental samples by detecting uptake of isotope-labelled substrates using nano-scale secondary ion mass spectrometry (nanoSIMS). Recent studies have demonstrated that sample preparation can decrease C and N enrichment in bacterial cells, resulting in underestimates of activity. Here, we explore this effect with a variety of preparation types, microbial lineages and isotope labels to determine its consistency and therefore potential for correction.