Photo-TROPHICATION · Photo-TROPHICATION: Impact of eutrophication on lake carbon fluxes driven by Aerobic Anoxygenic Phototrophic bacteria.

Anthropogenic disturbances in aquatic environments are causing carbon cycle imbalance and eutrophication. Bacteria perform crucial roles in the seasonal succession of aquatic communities and play a key role in the transfer of dissolved organic carbon to the upper trophic levels through the microbial loop. Aerobic anoxygenic phototrophic (AAP) bacteria harvest energy from light through bacteriochlorophyll reaction centers to supply their heterotrophic metabolism. AAP bacteria undergo large seasonal oscillations in abundance and community composition and are linked to phytoplankton bloom in freshwaters, reaching up to 20-30% of total bacterial community during their peaks. AAP use dissolved organic matter released by phytoplankton bloom, and since they have larger size and are under higher grazing pressure, critically participate in the microbial loop. AAP community is driven by the availability of carbon and phosphorus, elements that condition the lake’s trophic status. The aim of this project is to study how eutrophication is changing the fluxes of carbon that AAP bacteria drive in the environment through respiration and carbon assimilation. Environmental dark and infrared (IR) microbial respiration measurements will decipher the impact that photoheterotrophy has on microbial respiration in different trophic status lakes. Additionally, a novel combination of IR-epifluorescence microscopy with NanoSIMS analysis is proposed to quantify the phytoplankton derived carbon assimilation rates by AAP bacteria in different trophic status lakes. Finally, a unique monthly, 12-years long metagenomic and environmental survey from 4 different trophic status lakes (oligotrophic to eutrophic) will decipher the how the eutrophication is changing the AAP community composition and their genetic repertoire, aiding in the adequate management and restoration of eutrophic environments by providing information about the microbial community changes driven by eutrophication.