Distribution of the verrucomicrobial clade Spartobacteria along a salinity gradient in the Baltic Sea

A recent pyrosequencing study along the whole Baltic Sea salinity transect identified members of the Verrucomicrobia class Spartobacteria as an important component of Baltic Sea bacterioplankton. In this study, catalysed reporter deposition-fluorescence in situ hybridization was used for cellular quantification. The published probes VER47 and SPA714 were optimized for samples from the Baltic Sea and a new, specific probe (SPA476) was used to quantify the dominant spartobacterial lineage LD29'. The results confirmed that in the brackish surface waters of the Baltic Sea Spartobacteria comprise an important component, constituting up to 12% of all bacteria. The positive correlation and physical association of Spartobacteria with phytoplankton suggest their involvement in the utilization of phytoplankton-derived organic matter in the Baltic Sea.