Transcriptome analyses of Naegleria sp., Effects of photosynthetic traits of bacterial prey on predatory amoebae.

Photosynthesis generates reactive oxygen species (ROS) under light condition which damages the cell. Therefore, when unicellular transparent organisms feed on phototrophs in the daytime, light reaches the photosystems of the engulfed prey which probably generates higher levels of ROS inside the predator cells. In order to understand how unicellular predators cope with the photosynthetic oxidative stress, we examined the change in transcriptome of nonphotosynthetic predatory amoeba (Naegleria sp.) feeding on a cyanobacterium (Synechococcus elongatus PCC 7942), upon illumination. As a negative control, S. elongates, which reduced their photosynthetic pigments under a nitrogen-depleted condition and thus reduced photosynthetic ability, was used. In addition, Naegleria sp. was also grown in an organic medium without bacterial prey to examine effects of light stimulus on the amoeba, which is not related to photosynthetic traits of prey. Moreover, to examine effects of chlorophyll and ROS on amoebae, changes in transcriptome of the amoeba were examined under following conditions. Amoebae feeding on E. coli stained with or without chlorophyll a were illuminated; amoebae grown in an organic medium with Rose bengal (singlet oxygen generator under light) without bacterial preys were illuminated; Hydrogen peroxide was added to amoebae cultured in an organic medium without bacterial preys under continuous dark.