Microbes in springs in Iceland

Two endemic subterranean freshwater amphipod species, Crangonyx islandicus and Crymostygius thingvallensis inhabit groundwater in Icelandic lava fields. Divergent mtDNA lineages of C. islandicus, in different regions of Iceland, indicate that the species survived the Ice age in Iceland, in separated groundwater watersheds. These findings show strong evidence for an old groundwater ecosystem in Iceland, which might be based on chemoautotrophy. Similar systems are found in various places around the world, commonly in limestone karst where concentration of sulphur is high in the groundwater. That is considerably different from the cold groundwater springs where C. islandicus is found, but they are mostly found at the edges of basaltic lava fields. With combination of eDNA and metabarcoding, the microbial diversity of this peculiar system can now be revealed. Results show that the microbial community of the amphipods are dominated by chemolithoheterotrophs possibly capable of utilising iron and manganese as energy source. These same groups are not found to be as abundant in the spring sources indicating they are confined to the amphipods. The microbial community in the spring sources reflects that this is a three-way ecotone with species from the surface water, groundwater and the overlaying terrestrial ecosystem present. The microbial spring community is shaped by pH at the local scale while on regional scale other factors have impacts such as geographical location, temperature and the presence of fish. Only few chemolithoautotrophic taxa are found in this system indicating that they are not the greatest contributors to the primary production.