The effect of light on microbial uptake of organic substrates for cruise AMT20 (JC053)

This dataset consists of measurements of microbial organic substrate uptake rates in the presence and absence of light. In total, adenosine-tri-phosphate and methionine uptake rates of low nucleic acid containing bacteria and <i>Prochlorococcus</i> cyanobacteria were measured during the Atlantic Meridional Transect programme cruise 20 (AMT20, JC053) between 14th October and 21st November 2010. Sampling was restricted to the North Atlantic gyre. Pre-dawn seawater samples were collected from 20 m depth in 20 L Niskin bottles attached to a standard conductivity-temperature-depth profiler. Experiments were set up for dark and light measurements in a dark room. Light incubation experiments were placed in a 6-L water tank illuminated by a warm white light-emitting diode (LED) array. Parallel dark incubations were done in a similar water tank but were isolated from light. All experiments were run at ambient temperatures controlled by refrigerated water bath. Four 1.6 ml samples were inoculated with 0.5nM L-[³⁵S] methionine or 0.1–0.4nM [α ³³P]-ATP, and incubated for 2h in the light or dark before being fixed with 1% (w/v) paraformaldehyde. Subsequently, different bacterial populations were sorted according to light-scattering properties (90° or side light scatter, SSC) and relative concentration of SYBR Green I stain per particle (green fluorescence; FL1, 530 ± 30 nm) using a FACSort instrument (Becton Dickinson, UK). Radio-assaying of samples was carried out using a liquid scintillation counter (Tri-Carb 3100TR, Perkin-Elmer, Beaconsfield, UK).