Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Parameters
• Instruments
• Project Information
• Funding

Citation note: Sabrina Glynn and Kaycie Lanpher are co-first authors for this dataset

This was a highly collaborative project, and methods regarding community composition are provided by the Scripps Ecological Observatory while environmental and chlorophyll methods are provided by the Southern California Coastal Ocean Observing System. 

Metabolic rates were measured using two assays: phosphate uptake and ATP phosphorylation. Seawater was collected from the Ellen Browning Scripps Memorial Pier at the Scripps Institution of Oceanography (SIO) in La Jolla, California (32°52′1.1″N, 117°15′25.7″W). The seawater was collected just below the surface in acid clean, sample rinsed HDPE bottles using a crane located in the Scripps Pier Laboratory. The seawater was immediately pre-filtered with 250 μm nylon mesh into acid clean, sample-rinsed polycarbonate bottles. 

For both assays, seawater was collected, prefiltered, and aliquoted into triplicate incubation bottles. Radioactive 32P-PO4 was added to each bottle, with this tracer addition marking the beginning of the time course (time zero), with samples collected at specified intervals afterward. For the phosphate uptake assay, incubation water was filtered after a designated incubation period of less than 30 minutes, and particulate material was captured on a GF-75 filter with a nominal pore size of 0.3um). For the ATP-phosphorylation assay, samples were filtered as quickly as possible post-spike (after addition of radioactive 32P-PO4). The filters were then processed to preserve ATP by boiling them in Tris buffer and transferring the supernatant to HPLC.  Radioactive ATP was purified and collection in fractions using preparative HPLC. Radioactivity in all samples was quantified using a liquid scintillation counter. Additonal details are provided in Lanpher & Popendorf, 2022. 

Flow cytometry cell counts were collected on a BD Accuri in two methods-- one for autofluorescence (chlorophyll containing small cells) and one for total cells (DNA stain was used to fluoresce all cells).

Phosphorus stocks were quantified using the molybdenum blue method and spectrophotometry (phosphate) or combustion and acid hydrolysis to convert organic phosphorus to phosphate then subsequent molybdenum blue processing (dissolved organic phosphorus, and particulate phosphorus but from a filter). ATP concentration was measured using the firefly luciferin-luciferase method.

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NSF Award Abstract:

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).

Marine microbes, including single-celled bacteria, archaea, and eukarya, are the main drivers of carbon and energy transformations in the ocean. The efficiency of the microbial loop at transforming dissolved nutrients into biomass and up the food web is defined by the individual activities of the microbial community. Unfortunately, current methods for characterizing microbial activities in the marine environment are biased, with most direct measurements focusing on heterotrophic microbes that respire carbon dioxide in oxygenated waters. These measurements exclude a large diversity of microbes that play major roles in ocean nutrient cycles, including photosynthesizes and chemotrophs as well as microbes in low oxygen, anoxic waters. This project will measure the activity of microbial organisms through novel applications of the adenylate energy system, which is used by all organisms and in almost all metabolic pathways. This work will focus on sites in the California Current Ecosystem with a wide range of oceanographic conditions and variable microbial communities. These locations include low oxygen canyons representative of oxygen minimum zones (OMZs), upwelling locations reflecting eastern boundary currents, and temporally dynamic coastal sites. Within the planned sampling, support will be allocated for undergraduate students to join shipboard efforts to help with seawater sampling and gain experience conducting oceanographic research. The datasets produced from these sampling efforts will be used to develop predictive models of microbial metabolism (activity) that can be applied to other oceanographic regions, based on community structure, abundance, and geochemical parameters across time and environmental concentrations.

The highly productive California Current Ecosystem is subjected to seasonal successions of phytoplankton communities, with diatom and dinoflagellate dominance coinciding with upwelling. The ability of these phytoplankton groups to convert nutrients into biomass have impacts on primary productivity, biogeochemical cycles, and the microbial loop. Hypoxic environments shift the microbial community towards anaerobes and chemotrophs, which have unique metabolisms and differential efficiencies converting acquired carbon sources into biomass and energy. Therefore, the microbial loop efficiency in OMZs is likely to be directly impacted by microbial community structure, but precisely defining these differences in microbial activity has been hampered by biased sampling techniques. This project will address the hypotheses that microbial activity, in terms of energy storage, metabolic rates, and growth rates will be directly liked to and predicted by phytoplankton community structure and abundances in seasonal upwelling systems. Additionally, microbial activities in OMZs are linked directly to the implementation of anaerobic metabolic strategies and can thus be predicted by changes in community structure. Microbial activity will be characterized using high throughput applications of novel measures of the energy charge and adenosine triphosphate (ATP) turnover rates while the microbial community structure will be defined with 16S and 18S rRNA gene amplicon sequencing. Two dedicated, single day cruises to the La Jolla and Scripps Canyons located within the California Bight, and containing known OMZs will be conducted. Additionally, microbial activity measurements will be incorporated into an on-going time-series that is sampled for microbial community structure twice-a-week at the Scripps Institute of Oceanography pier in La Jolla, CA. Measurements from the cruises and time-series will be used to develop predictive models of microbial metabolism based on community structure, abundance, and geochemical parameters across time and within known OMZs using self-organizing maps (SOMs) and random forest regression. Therefore, this project will produce predictive models that can be generalized to broader ocean regions in addition to datasets with unprecedented resolution of natural microbial activity across time and environmental conditions.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.