Co-occurence and co-metabolism of phototrophic and heterotrophic microbial communities in the Baltic Sea

Sammanfattning: In the marine water column, microbial autotrophs and heterotrophs coexist forming the beginning of the food chain which sustains the whole biological system. Both groups play a vital role in the microbial loop. Primary producers, such as algae and Cyanobacteria, use available nutrients in the water (and atmospheric CO2) to release energy, in the form of DOM (dissolved organic matter). Heterotrophic bacteria can then use this energy to remineralise recalcitrant and semilable organic matter present in the water column. Interactions between and among these communities are complex and dependent on several factors such as temperature, salinity, availability of nutrients (C, P, N among others). This remineralisation process is possible, in part, because of extracellular enzymes, produced by the microbial community to hydrolyse large molecules (> 600 Da). In this study, samples were isolated from the Baltic Sea. Then Illumina Miseq amplicon sequencing and an enzymatic assay were performed, with the objective of identifying the microbial community and determine patterns of co-occurrence as well as access extracellular enzymatic activity (EEA) in those same communities. Several taxa were identified through sequencing. Among them: heterotrophic bacteria (mainly from the Proteobacteria phylum), Cyanobacteria (mainly Synechococcus) and green algae with Trebouxiophyceae as the dominant class. The EEA showed activity consistent with summer Cyanobacterial blooms, with enzyme activity associated with phosphate mineralisation and cellulose degradation.