Figure 6.

Responses of the two mixotrophic Ochromonas isolates to different environmental conditions. Both isolates reach highest growth rates under saturating light and prey availability. The obligate mixotroph (CCMP1393, top row) has higher chlorophyll content under low‐light compared to high‐light conditions and when prey is available compared to prey‐deplete conditions. Rates of both carbon fixation in the Calvin–Benson cycle (CBC) and ingestion of prey are highest under mixotrophic conditions under high light. Reducing equivalents are exchanged between the plastid and mitochondria linking the photosynthetic with the respirational electron transport chain. Growth is most strongly reduced at low‐light intensities. In contrast, the facultative mixotroph (CCMP2951, bottom row) increases its chlorophyll content when prey is depleted at high light, while in the presence of prey light has little impact on chlorophyll content. Rates of ingestion are highest under low‐light condition and maximum rates of carbon fixation are reached when prey is depleted. Export of reducing equivalents from the chloroplast to mitochondria only acts as overflow during high‐light condition. Growth is most strongly reduced in the absence of prey. AOX, alternative oxidase; TCA, tricarboxylic acid cycle; C_I, respiratory complex I; C_III, respiratory complex III; PSII, photosystem II; PTOX, plastid terminal oxidase; PSI, photosystem I; CBC, Calvin–Benson cycle. [Color figure can be viewed at http://www.wileyonlinelibrary.com]