Fig. 1: Habitat and establishment of the axenic coculture of the dinoflagellate N. aeruginosum and the cryptomonad Chroomonas sp. Dc01.

a The pond in Hokkaido prefecture, Japan from which N. aeruginosum and Chroomonas sp. Dc01 were collected. b Micrograph of a water sample from the pond showing the coexistence of N. aeruginosum and unicellular algae. The cells were collected on September 24, 2010 [19]. Scale bar = 10 μm. c Micrograph showing the axenic coculture of N. aeruginosum and Chroomonas sp. The coculture contains Chroomonas sp. as a source kleptoplast of N. aeruginosum as well as N. aeruginosum cells with or without kleptoplast, and cysts. Scale bar = 50 μm. d Photograph of a plankton-net filter and a schematic drawing showing the separation of N. aeruginosum cells with Chroomonas sp.-derived kleptoplasts from free Chroomonas sp. (those had not been ingested by N. aeruginosum). A 5-µm diameter plankton-net filter was attached to the bottom of the sieve. The coculture of N. aeruginosum and Chroomonas sp. was filtrated to separate free Chroomonas sp. from N. aeruginosum with kleptoplasts. N. aeruginosum cells on the filter were washed several times before further experiments. e Micrographs showing the coculture of N. aeruginosum cells with Chroomonas sp.-derived kleptoplasts and free Chroomonas sp. (left), filtered N. aeruginosum cells that are separated from free Chroomonas sp. (middle), and free Chroomonas sp. in the flow-through fraction. Scale bar = 10 μm.