Temporal dynamics in a red alga dominated geothermal feature in Yellowstone National Park.

Alga-dominated geothermal spring communities in Yellowstone National Park (YNP), USA, have been the focus of many studies, however, relatively little is known about the composition and community interactions which underpin these ecosystems. Our goal was to determine, in three neighboring yet distinct environments in Lemonade Creek, YNP, how cells cope with abiotic stressors over the diurnal cycle. All three environments are colonized by two photosynthetic lineages, and , both of which are extremophilic Cyanidiophyceae red algae. , a highly specialized obligate photoautotroph, dominated cell counts at all three Lemonade Creek environments. The cell cycle of in YNP matched that observed in synchronized cultures, suggesting that light availability plays a strong role in constraining growth of this alga in its natural habitat. Surprisingly, the mixotrophic and physiologically more flexible , was a minor component of these algal populations. Arsenic detoxification at Lemonade Creek occurred complementary gene expression by different eukaryotic and prokaryotic lineages, consistent with this function being shared by the microbial community, rather than individual lineages completing the entire pathway. These results demonstrate the highly structured nature of these extreme habitats, particularly regarding arsenic detoxification.