Dataset: Flow cytometry data from Incurrent and Excurrent flow

A ZE5 Cell Analyzer flow cytometer (Bio-Rad, Hercules, CA, USA) was used to measure optical properties of single cells from each sample and quantify requested populations. To ensure accurate calibration of the flow cytometer, ZE5 QC beads (Bio-Rad, Hercules, CA, USA) were run daily.

Picophytoplankton (less than 3 µm) and nanophytoplankton (3-20 µm) were analyzed using a slight modification of the method described in Lomas et al., 2010. Immediately after thawing at room temperature, 300-400 µl of sample was prescreened through 70 µm mesh and run at a flow rate of 1 µl sec-1. Particles were excited with a 488 nm blue laser and data acquisition was triggered on red fluorescence. Signals were recorded from detectors with bandpass filters for forward scatter (FSC), right angle light scatter (SSC) and fluorescence emission in red (692/80 nm) indicative of chlorophyll a, and orange (593/52 nm) for phycoerythrin. Data files were analyzed from logarithmic dot plots based on fluorescence and characteristic light scattering properties (DuRand & Olson, 1996) using FlowJo 10.6 software (Becton Dickinson & Company, San Jose, CA, USA). Total pico and nano phytoplankton populations were identified based upon cell size and red fluorescence. Phycoerythrin containing cell populations were determined by orange fluorescence. Based upon these gating criteria, the number of cells in each identified population was enumerated and converted to cell abundances using the processed sample volume and adjusted for dilution by preservative.

For total bacteria analysis, samples were thawed, diluted 1:10 with Tris EDTA (TE) Buffer pH 8.0 and stained using a 10x working stock of SYBR Green I Nucleic Acid Stain (Thermofisher Scientific, USA) at room temperature in the dark for 15 min using the protocol of Marie et al. (2005). At a flow rate of 0.5 µl sec-1, 180 µl of the diluted sample was run. Particles were excited with a 488 nm blue 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 from two logarithmic scatter plots based on fluorescence and characteristic light scattering properties. Total bacteria counts were identified based on size and presence of green fluorescence and counts were converted to cell abundances using the volume of sample processed including adjustments for preservation, dilution and staining.