Dataset: Laboratory-based growth studies with multiple G. huxleyi strains for genome sequencing

All G. huxleyi isolates were obtained from either the National Center for Marine Algae and Microbiota (East Boothbay, ME) or the Roscoff Culture Collection (Roscoff, France) and maintained in incubators with ~100 µE m-2 s-1 light on a 14:10 light:dark cycle in autoclaved L1 media with a 0.2-µm filtered Vineyard Sound (MA) seawater base. Isolates were grown at different temperatures, as determined by their collection location (reported in strain metadata from NCMA and/or Roscoff; e.g., CCMP371 was collected in June 1987 in the Sargasso Sea at 32°N, 62°W with a culture collection maintenance temperature of 20 °C). To generate enough biomass needed for downstream genome sequencing (details reported elsewhere), large (1 L) batch cultures of each isolate were grown. For each separate isolate, a 25 mL nutrient-replete (L1) culture was used to inoculate 1 L nutrient-replete (L1) media in a Fernbach flask. No replicate cultures were grown for this experiment, as replicates were not necessary given the goal of obtaining DNA for genome sequencing.

Growth was monitored daily at the same time of day by in vivo chlorophyll fluorescence (relative fluorescence units, RFUs) on a Turner Designs Aquafluor handheld fluorometer (in vivo chlorophyll a channel). Briefly, each culture was mixed by swirling 3 times clockwise and then 3 times counterclockwise before aseptically removing a 2 mL subsample with a serological pipette. The subsample was transferred to a 10 mm × 10 mm methacrylate cuvette and placed in the Aquafluor for RFU measurement. A blank measurement was also taken daily using deionized water in place of a culture sample in the same type of cuvette. The RFU value obtained from the blank was subtracted from the RFU value of the culture for a “blank-corrected” RFU. Negative values for the blank were a result of instrument drift and were subtracted as described above. No RFUs in the dataset were missing or anomalous.

The exponential population growth rate for each G. huxleyi strain was calculated by measuring changes in blank-corrected RFUs (in vivo chlorophyll a) as a proxy for biomass over time during the exponential growth phase (minimally 4 days), using the formula µ = (ln(N2) - ln(N1))/t2-t1, where N1 is the in vivo chlorophyll a (RFU) at the start, N2 is the in vivo chlorophyll a (RFU) at the end, t1 is the first timepoint (day), and t2 is the final timepoint (day). RFUs were ln-transformed and fitted with a linear regression of ln(RFU) versus time (days). The regression slope over the most linear portion (where R2 > 98%) of the growth curve was taken as the best estimate of mean daily population growth rate.

The resulting datasets from applying this method included G. huxleyi strain growth conditions, G. huxleyi growth (biomass proxied by relative fluorescence units from in vivo chlorophyll a), and G. huxleyi exponential growth rates.