High diversity of planktonic prokaryotes in Arctic Kongsfjorden seawaters in summer 2015

Kongsfjorden is a typical glacier fjord in the European Arctic. In order to know the distribution and diversity of planktonic prokaryotes in the fjord subjected to strong physical gradient related with local glacier dynamics, prokaryote communities along a transect extending from the outer to the inner fjord was investigated in the summer of 2015 using 454 pyrosequencing of archaeal and bacterial 16S rRNA genes. Higher diversity and species richness were detected in Bacteria than in Archaea in each sample. Archaeal 16S rRNA gene sequences were not detected in the outer area of the fjord. Nitrososphaeria within the phylum Crenarchaeota and Poseidoniia within the Thermoplasmatota were two dominant archaeal groups in the fjord. At the genus level, Nitrosopumilus, Nitrosopelagicus, MGIIa-L1, and MGIIb–O2 dominated seawater archaeal communities. Higher abundances of Poseidoniale-related archaea were observed in the deep water than in the surface water. The Proteobacteria, Bacteroidota, and Actinobacteriota dominated the planktonic bacterial communities, with Verrucomicrobiota (represented by Verrucomicrobiae) dominating the middle area of the fjord. At the class level, Bacteroidia, Alphaproteobacteria, Gammaproteobacteria, and Actinobacteria dominated the bacterial communities within Kongsfjorden. Sequences affiliated with genera Polaribacter and Yoonia were frequently detected in the fjord. Results suggest that planktonic archaeal and bacterial community compositions in Kongsfjorden can be driven by different major environmental factors.