Prokaryotic ultramicroforms in a Sphagnum peat bog of upper Volga catchment

Abstract

The waters of small lakes located in swampy catchment areas of upper Volga contain considerable amounts of ultrasmall microbial cells that pass through 0.22-μm-pore-size filters. As shown in our previous study [1], most of these cells represent the bacterial genera Herbaspirillum, Herminiimonas, Curvibacter, and Burkholderia of the class Betaproteobacteria, as well as euryarchaea of the uncharacterized clade LDS. The aim of the present study was to investigate the possible effect of the waters draining swampy areas on the composition of the filterable microbial fraction in lakes fed by swampy catchments. To address this question molecular identification was performed of prokaryotic ultramicroforms in the peat of the ombrotrophic Sphagnum bog Obukhovskoe, located, like the lakes studied previously [1], in the Mologa-Sheksna catchment area. The number of filterable microorganisms in 1 g wet peat was 3.8 × 106 cells, or 0.5% of total microbial cell number in the peat. From the DNA of the filterable cell fraction, 100 clones of bacterial and 77 clones of archaeal 16S rRNA genes were obtained. The bacterial clone library contained 16S rRNA gene sequences representing the classes Beta- and Gammaproteobacteria (the genera Janthinobacterium and Pseudomonas, respectively) and the phylum Bacteroidetes (the genera Chryseobacterium and Epilithonimonas) and differed significantly from the clone library of bacterial ultramicroforms of lake water. By contrast, the pools of filterable archaea in bogs and lakes were essentially similar. They were represented by the euryarchaeal clade LDS and methanogens of the orders Methanobacteriales and Methanosarcinales. Additionally, the pool of filterable archaea of the bog included methanogens of the order Methanomicrobiales and representatives of the uncharacterized euryarchaeal clade RC-V (Rice Cluster V) and of the phylum Thaumarchaeota.