ERP113543 PRJEB31036 ena-STUDY-UMEA UNIVERSITY-30-01-2019-14:20:49:212-101 Microbial population dynamics in a photobioreactor located in Northern Sweden Municipal wastewater treatment coupled with microalgal cultivation is considered a higher efficient and cost-effective strategy compared to conventional treatment systems. The process, however, remains challenging in Nordic regions due to the unfavorable environmental conditions. In this work, a pilot-scale high-rate algal pond (HRAP) located in Northern Sweden was inoculated with the collection strain S. dimorphus UTEX417 in spring 2015 and operated until autumn. Microbial diversity of eukaryotic and prokaryotic communities in the photobioreactor and their dynamics over time was revealed by high-throughput metabarcoding of 18S and 16S rRNA genes and correlated with light, temperature, dissolved oxygen, biomass and inorganic nutrients concentrations. S. dimorphus was initially stable in the culture, but other microalgae appeared later and co-dominate the system as a consequence of zooplankton predation in summer, which strongly inhibited the original microalgal strain. Desmodesmus, Pseudocharaciopsis, Chlorella, Characium and Oocystis were the main competitor algal species. Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria were the most abundant bacterial phyla in the HRAP, whereas Cyanobacteria only appeared in the second part of the season. The structure of prokaryotic and zooplanktonic communities clearly changed with time, suggesting seasonal variation. Variations of the environmental parameters measured inside the culture partially correlated with changes in the microbial composition, especially for prokaryotes. Our results give a first insight on the microbial composition and dynamics of a HRAP located in Northern Sweden and provide useful information on the type and robustness of microalgal and bacterial species colonizing the culture in different months and under different environmental conditions. Microbial population dynamics in a microalgae-based municipal wastewater treatment photobioreactor located in Northern Sweden Municipal wastewater treatment coupled with microalgal cultivation is considered a higher efficient and cost-effective strategy compared to conventional treatment systems. The process, however, remains challenging in Nordic regions due to the unfavorable environmental conditions. In this work, a pilot-scale high-rate algal pond (HRAP) located in Northern Sweden was inoculated with the collection strain S. dimorphus UTEX417 in spring 2015 and operated until autumn. Microbial diversity of eukaryotic and prokaryotic communities in the photobioreactor and their dynamics over time was revealed by high-throughput metabarcoding of 18S and 16S rRNA genes and correlated with light, temperature, dissolved oxygen, biomass and inorganic nutrients concentrations. S. dimorphus was initially stable in the culture, but other microalgae appeared later and co-dominate the system as a consequence of zooplankton predation in summer, which strongly inhibited the original microalgal strain. Desmodesmus, Pseudocharaciopsis, Chlorella, Characium and Oocystis were the main competitor algal species. Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria were the most abundant bacterial phyla in the HRAP, whereas Cyanobacteria only appeared in the second part of the season. The structure of prokaryotic and zooplanktonic communities clearly changed with time, suggesting seasonal variation. Variations of the environmental parameters measured inside the culture partially correlated with changes in the microbial composition, especially for prokaryotes. Our results give a first insight on the microbial composition and dynamics of a HRAP located in Northern Sweden and provide useful information on the type and robustness of microalgal and bacterial species colonizing the culture in different months and under different environmental conditions. Bacterioplankton Photobioreactor Eukaryotic plankton Metabarcoding Scenedesmus Seasonal dynamics 16S rRNA gene ENA-FIRST-PUBLIC 2019-04-30 ENA-LAST-UPDATE 2019-03-28