Living in Vulcan's forge: Algal adaptation to stressful geothermal ponds on Vulcano Island (southern Italy) as a result of pre‐selective mutations

Abstract

SUMMARYFour species of eukaryotic algae proliferate in the sulfureous, acidic (pH 3.1) water of the largest geothermal pond on Vulcano Island (southern Italy). Consequently, this pond constitutes a natural laboratory for analysis of adaptation by phytoplankters to extremely stressful conditions. To distinguish between the pre‐selective or post‐selective origin of adaptation processes allowing the existence of phytoplankters in the pond, a Luria‐Delbrück fluctuation test was carried out with the chlorophycean Dictyosphaerium chlorelloides and the cyanobacterium Microcystis aeruginosa, both isolated from non‐extreme waters; natural water from the Vulcano Island pond was used as selective factor. Preselective, resistant D. chlorelloides cells appeared with a frequency of 4.7 × 10−7 per cell per generation. We propose that the micro‐algae inhabiting this stressful pond could be the descendents of chance mutants that arrived in the past or are even arriving at the present. The genetic adaptation of D. chlorelloides to Vulcano waters could help to explain the survival of photosynthesizers in very stressful geothermal waters during the Neoproterozoic ‘snowball Earth’, a period when primary production collapsed in the biosphere. On the other hand, adaptation to these conditions was not observed in M. aeruginosa, suggesting that cyanobacteria may not be able to develop any kind of adaptation to Vulcano pond water.