The effect of the diatom D. geminata and its associated microbiome on nutrient cycling of lakes and rivers at the Chilean Patagonia

The diatom Didymosphenia geminata has emerged as nuisance species in freshwater ecosystems around the world, developing thick mats of carbohydrate stalk material in ultraoligotrophic streams and lakes. D. geminata mats are nutrient-rich environments, that serve as substrate for a wide range of microorganisms capable of influencing biogeochemical cycles in their ecosystem. Therefore, the analysis of the microbiota associated to D. geminata mats, together with physical and chemical data, represents a pivot tool in our understanding of this invasive diatom's role on the biogeochemical cycles of affected lakes and rivers. We measured physical and chemical parameters and determined the bacteria and archaea communities attached to D. geminata mats from three different freshwater ecosystems located in the chilean Patagonia.

All studied ecosystems were poor in nutrients (i.e., carbon, phosphorous, and nitrogen), well oxygenated, and with a mean temperature of 9.3 ± 2.7 °C. The core microbiome of D. germinata mats was defined based on the taxa shared among samples. These taxa are dominated by psychrophilic microorganisms, including organic carbon degrading bacteria and heavy metals tolerant bacteria. The dominant genera were influenced by environmental conditions and included potential N₂-fixing members, suggesting a possible association between D. geminata and N-fixers. This association could represent an important input of N into these ecosystems, with potential greater consequences on nutrient cycling than previously thought.