Limnospira (Cyanobacteria) chemical fingerprint reveals local molecular adaptation

Limnospira can colonize a wide variety of environments ( e.g. freshwater, brackish, alkaline or alkaline-saline water) and develop permanent blooms that limit overshadowed adjacent photo-trophs diversity, especially in alkaline and saline environments. Previous phylogenomic analysis of Limnospira allowed us to distinguish two major phylogenetic clades (I and II) but failed to clearly segregate strains according to their respective habitats in terms of salinity or of biogeography. In the present work, we attempt to determine whether Limnospira display metabolic signatures specific to its different habitats, particularly brackish or alkaline-saline ecosystems, and question the impact of accessory genes repertoire on respective chemical adaptation. The study of the metabolomic diversity of 93 strains of Limnospira of the Paris Museum Collection, grown under standardized lab culture conditions, showed clearly distinct chemical fingerprints that were correlated with the respective biogeographic origin of the strains. The molecules that most discriminate the different Limnospira geographic groups are sugars, lipids, peptides, photosynthetic pigments, and antioxidant molecules. Interestingly, these molecule enrichments might represent adaptation traits to the local conditions encountered in their respective sampling environments concerning salinity, light and oxidative stress. We hypothesize that within extreme environments, such as those colonized by Limnospira , flexible genes that are necessary for the adaptation to specific local environmental conditions ( e.g. salinity, light, oxidative pressure) are selected, leading to the specific production of certain metabolites involved in stress defence mechanisms. Importance Cyanobacteria are a group of photoautotrophic microorganisms that have colonized a wide range of environments around the world. Phylogenomic analysis of Limnospira platensis allowed to distinguish two major phylogenetic clades (I and II) but failed to clearly segregate strains following their habitats in terms of salinity or biogeography. One can presume that the genes found within this variable portion of the genome of these clades could be involved in L. platensis adaptation to local environmental conditions. In the present paper, we attempt to determine whether Limnospira platensis display metabolic signatures specific for its different habitats, particularly brackish or alkaline-saline ecosystems, and question the impact of accessory gene repertoire on respective chemical adaptation.