Stratification of Prokaryotic Communities in the White Sea Bottom Sediments

Investigation of prokaryotic communities from different horizons of the bottom sediments in the Kandalaksha Gulf, White Sea revealed two characteristic groups of sampling points. The first group demonstrated stratification of prokaryotic communities depending on the horizon depth, while the second one, with uniform prokaryotic communities, was typical of the sections with active organic matter decomposition. Microorganisms involved in decomposition of labile organic compounds (Woeseia and Sandaracinaceae), as well as sulfate reducers (SEEP-SRB1 and Sva0081) predominated in the upper horizons of the stratified sediments (the first group of samples). In the lower layers (30 and 50 cm), the share of microorganisms potentially involved in the degradation of complex compounds (e.g., Desulfatiglans, Hyphomicrobiaceae, and Mycobacterium) increased. The share of prokaryotes with unknown metabolism, such as JS1, SG8-4, WCHB1-81, Aerophobales, and S085, increased as well. Thus, the structure of prokaryotic communities was affected by the presence and abundance of organic matter, which decreased with depth.