Viral and Bacterial Counts from Fkt_240412 Cruise to the ETSP Oxygen Minimum Zone

Samples were collected on the Falkor (too) cruise Fkt240412 to the ETSP OMZ of the coast of Chile at one nearshore and one offshore station. Data comes from samples from one vertical depth profile taken at each station. The data table includes associated CTD data including dissolved oxygen (umol/kg), salinity (ppm) and temperature (C). For more information on additional data collected during this cruise, please visit https://schmidtocean.org/cruise/microbes-in-oxygen-minimum-zones/#data Sample collection and preservation Two one milliliter aliquots of raw seawater per depth were collected from niskin bottles, stored in cryotubes and preserved with 10ul 50% EM-grade glutaraldehyde to a final concentration of 0.5% glutaraldehyde per sample (Brussaard 2004). Samples were then incubated at 4C for 60 minutes and snap frozen via tube immersion in -80C cooled ethanol for 60 seconds prior to storage as -80C. Flow Cytometry Counts A ZE5 Cell Analyzer flow cytometer (Bio-Rad, Hercules, CA, USA) was used to measure optical properties of viral and bacterial particles from each sample. To ensure accurate calibration of the flow cytometer, ZE5 QC beads (Bio-Rad, Hercules, CA, USA) were run daily. After thawing, samples were diluted 1:10 with 0.02um filter sterilized TE Buffer pH 8.0 for bacterial counts, and similarly at a dilution of 1:100 for viral particle counts. Diluted samples were stained using a 10x working stock of SYBRTM Green I Nucleic Acid Stain (Thermofisher Scientific, USA) to a final dilution of 5 * 10^-5 SYBRTM Green I commercial solution (Brussaard 2004). Stained diluted samples were then incubated at room temperature in the dark for 15 min (Marie et al. 2005; Brussaard et al. 2000). 180 µl of sample was run at a flow rate of 0.5 µl sec-1. Particles were excited with a 488 nm blue excitation laser and data acquisition was triggered on green fluorescence. Signals were recorded from detectors with bandpass filters for forward scatter (FSC), right angle light scatter (SSC) and fluorescence emission in green (525/35nm). Data files were analyzed using FlowJo 10.6 software (Becton Dickinson & Company, San Jose, CA, USA). Viral and bacterial particles were identified from two logarithmic scatter plots based on fluorescence and characteristic light scattering properties. Total bacteria and viral particle counts are identified based on size and green fluorescence and counts were converted to abundances using the volume of sample processed. Brussaard, C. P., D. Marie, and G. Bratbak. 2000. “Flow Cytometric Detection of Viruses.” Journal of Virological Methods 85 (1–2): 175–82. Brussaard, Corina P. D. 2004. “Optimization of Procedures for Counting Viruses by Flow Cytometry.” Applied and Environmental Microbiology 70 (3): 1506–13. Marie, D., N. Simon, and D. Vaulot. 2005. “Phytoplankton Cell Counting by Flow Cytometry.” Algal Culturing Techniques, 253–67.