Differential timing for glucose assimilation in Prochlorococcus and coexistent microbial populations in the North Pacific Subtropical Gyre

Obtain cell abundances for marine microorganisms, particularly Prochlorococcus, over a diel cycle in the surface seawater of the North Pacific subtropical gyre. Sampling times of the day are given next to the file name: U-HOT296-FCM-1_001.fcs 6:20:00 AM U-HOT296-FCM-2_001.fcs 6:20:00 AM U-HOT296-FCM-3_001.fcs 12:20:00 PM U-HOT296-FCM-4_001.fcs 12:20:00 PM U-HOT296-FCM-5_001.fcs 6:20:00 PM U-HOT296-FCM-6_001.fcs 6:20:00 PM U-HOT296-FCM-7_001.fcs 12:20:00 AM U-HOT296-FCM-8_001.fcs 12:20:00 AM U-HOT296-FCM-9_002.fcs 6:20:00 AM U-HOT296-FCM-10_002.fcs 6:20:00 AM U-HOT296-FCM-11_001.fcs 12:20:00 PM U-HOT296-FCM-12_001.fcs 12:20:00 PM U-HOT296-FCM-13_001.fcs 6:20:00 PM U-HOT296-FCM-14_001.fcs 6:20:00 PM U-HOT296-FCM-15_001.fcs 12:20:00 AM U-HOT296-FCM-16_001.fcs 12:20:00 AM U-HOT296-FCM-18_001.fcs 6:20:00 AM U-HOT296-FCM-17_001.fcs 6:20:00 AM U-HOT296-FCM-19_001.fcs 12:20:00 PM U-HOT296-FCM-20_001.fcs 12:20:00 PM
Notes:
Subsamples for flow cytometric cell counts were taken in duplicate 2 ml samples, fixed with paraformaldehyde (0.24% final concentration) and incubated for 15 min in the dark before flash freezing and storing at -80˚C until analysis back in the laboratory. Phytoplankton groups were enumerated using a BD Influx flow cytometer equipped with a forward scatter (FSC) detector with small particle option (BD Biosciences, San Jose, CA, USA). Prochlorococcus, Synechococcus, Crocosphaera and pigmented eukaryotes (<5-µm (1)) were enumerated in unstained samples following published protocols (2). Briefly, cells were identified based on red fluorescence signals vs FSC, then further gated by FSC and orange fluorescence. The high phycoerythrin (orange) signal in Synechococcus and Crocosphaera was used to distinguish them from Prochlorococcus and pigmented eukaryotes. A 488 plus a 457 nm (200 and 300 mW solid state, respectively) laser focused into the same pinhole resolved dim surface Prochlorococcus population from background noise in a FSC vs red fluorescence plot. Potential particle aggregates were discarded using a pulse width vs. forward scatter plot. Calibration and alignment were done using 1-μm yellow-green microspheres (Polysciences, USA). 1. Duhamel S, Kim E, Sprung B, Anderson OR. Small pigmented eukaryotes play a major role in carbon cycling in the P-depleted western subtropical North Atlantic, which may be supported by mixotrophy. Limnol Oceanogr. 2019;64:2424-40. 2. Bock N, Van Wambeke F, Dion M, Duhamel S. Microbial community structure in the western tropical South Pacific. Biogeosciences. 2018;15(12):3909-25.