Acidophilic green algal genome provides insights into adaptation to an acidic environment

Significance Extremely acidic environments are scattered worldwide, and their ecosystems are supported by acidophilic microalgae as primary producers. To understand how acidophilic algae evolved from their respective neutrophilic ancestors, we determined the draft genome sequence of the acidophilic green alga Chlamydomonas eustigma and performed comparative genome analyses between C . eustigma and its neutrophilic relative Chlamydomonas reinhardtii . The results suggest that higher expression of heat-shock proteins and H + -ATPase, loss of some metabolic pathways that acidify cytosol, and acquisition of metal-detoxifying genes by horizontal gene transfer have played important roles in the adaptation to acidic environments. These features are also found in other acidophilic green and red algae, suggesting the existence of common mechanisms in the adaptation to acidic environments.