Addressing the Joint Impact of Temperature and pH on Adaptation in the Time of Climate Change.

Global warming and acidification of the global ocean are two important manifestations of the ongoing climate change. To characterize their joint impact on adaptation and fitness, we analyzed the temperature-dependent adaptation of at different pHs (7.0, 7.5, 8.0, 8.3 and 8.5) that mimic the pH of the world ocean in the past, present and future. Comparison of growth at 20, 25 and 30 °C show that higher temperature per se facilitates the logarithmic growth of in nutrient-rich environments in a pH-dependent manner. Further survival tests carried out in artificial seawater for 35 days revealed that cell culturability declined significantly upon incubation at 25 °C and 30 °C but not at 20 °C. Moreover, although acidification displayed a negative impact on cell culturability at 25 °C, it appeared to play a minor role at 30 °C, suggesting that elevated temperature, rather than pH, was the key player in the observed reduction of cell culturability. In addition, analyses of the stressed cell morphology and size distribution by epifluorescent microscopy indicates that likely exploits different adaptation strategies (e.g., acquisition of coccoid-like morphology) whose roles might differ depending on the temperature-pH combination.