Dataset: Bacterial Productivity measurement of bulk seawater and mesocosm experiments taken aboard the R/V Endeavor in the Western North Atlantic during the research cruise EN683 in May and June, 2022

Seawater was collected aboard R/V Endeavor during the research cruise EN683 (2022-05-24 to 2022-06-12). Samples were collected in one of three ways: bulk seawater from each station was collected into acid-washed 50 mL Falcon tubes from Niskin bottles mounted on a rosette, equipped with a CTD and triggered at specific depths; or from large volume (LV) mesocosm experiments sampled by pouring water from each mesocosm into an acid-washed 50 mL Falcon tube; or from Sargassum mesocosm experiments by submerging acid-washed 50 mL Falcon tubes into the incubation tank to collect surrounding water.

To 1.7ml triplicate subsamples and one killed control, isotopically diluted L-[3,4,5-3H(N)]-Leucine (PerkinElmer, NET460250UC, specific activity of 3.7 TBq/mmol) was added (20 nM final concentration). Samples and killed control were incubated between 6 and 36 hours at near in-situ temperature.  Live samples were killed with 100% (w/v) TCA and centrifuged (10,000 rpm at 4°C for 10 min) to pelletize cell material.  The supernatant liquid was removed and 1 mL of ice-cold 5% (w/v) TCA solution was added, followed by vortex mixing and centrifugation. Supernatant removal, mixing, and centrifugation were repeated using 1 mL of ice-cold 80% ethanol solution. Again, the supernatant liquid was removed and each sample was left to dry in a hood overnight.  After drying, 1 mL of scintillation cocktail (ScintiSafe 30% Cocktail, Fisher SX23-5) was added and left overnight so that precipitated proteins dissolve into scintillation fluid.  Incorporated radioactivity was measured using a PerkinElmer Tri-Carb 2910TR LSA scintillation counter for bulk, and PerkinElmer Tri-Carb 3110TR LSA for large volume (mesocosm) samples.  Radioactivity was compared to 1 mL of scintillation cocktail spiked with an identical amount of isotopically diluted L-[3,4,5-3H(N)]-Leucine that was added to samples. Incorporation rate was calculated by dividing sample radioactivity by incubation time.

For experiments using Exetainer vials, isotopically diluted L-[3,4,5-3H(N)]-Leucine addition was scaled to achieve 20 nM final concentrations in the ~ 3.0 mL volume Exetainer vial subsample.  The addition of TCA was also scaled accordingly. Vials were carefully and fully filled with subsample prior to capping to prevent leaking or cracking when pressure was applied.