Fig. 6: Comparison of growth rate at different light intensities between free Chroomonas sp. Dc01 and N. aeruginosum with kleptoplasts derived from Chroomonas sp. Dc01.
a To examine the cellular growth of N. aeruginosum with kleptoplasts, free Chroomonas sp. Dc01 was first removed from the coculture with illumination (10 µmol photons m−2 s−1) in order to inhibit N. aeruginosum from newly ingesting Chroomonas sp., and then the culture was exposed to the indicated light intensities. Changes in N. aeruginosum cell number for 5 days were determined. Free Chroomonas sp. Dc01 alone was simultaneously cultured in the same inorganic medium with illumination (10 µmol photons m−2 s−1) and then exposed to the indicated light intensities for 5 days. b Growth rates under the indicated light intensities. The growth rate (µ) was calculated as the difference between the natural logarithm of the cell number (N) at different time points (t, day 0–5) according to the following equation: µ = ln(Nt5/Nt0)/(t5−t0). The error bars represent standard deviation (three independent cultures). *P < 0.05; N.S., no significant difference (t-test). The changes in respective cell numbers are show in Supplementary Fig. 1. c To examine the effects of nuclei derived from Chroomonas sp. Dc01 on the growth/survival of N. aeruginosum in e and f, free Chroomonas sp. Dc01 was removed from the coculture with illumination (10 µmol photons m−2 s−1). N. aeruginosum with kleptoplasts were further cultured for 12 days until ~40% of the cells had lost nuclei derived from Chroomonas sp. Dc01. Then, from hour 0, the culture was kept at 10 µmol photons m−2 s−1 or subjected to 200 µmol photons m−2 s−1, and further cultured for 5 days. d Micrographs showing the change in the nucleus and kleptoplast derived from Chroomonas sp. in N. aeruginosum cells at 10 and 200 µmol photons m−2 s−1, respectively. Cells were stained with SYBR Green. Images of differential interference contrast (DIC), SYBR Green staining, and kleptoplast red fluorescence (Chl) are shown. The arrowhead indicates a nucleus derived from Chroomonas sp. For comparison, Chroomonas sp. Dc01 cells alone, which were cultured at 200 µmol photons m−2 s−1, are also shown. Scale bar = 10 μm. Changes in N. aeruginosum cell density (e) and ratio of N. aeruginosum cells possessing the nuclei derived from Chroomonas sp. Dc01 (f) at 10 and 200 µmol photons m−2 s−1. The error bars represent standard deviation (three independent cultures).
