Boreskov

THE STRUCTURE OF MICROBIAL COMMUNITY IN THE BOTTOM WATERLAYER OF LAKE BAIKAL AND POSSIBLE ROLE OF EUBACTERIAIN DESTRUCTION OF DIATOMSPP‐41Zakharova Yu.P. 1 , Kurilkina M.I. 1 , Likhoshvay Al.V. 1 , Shishlyannikov S.M. 1 , Petrova D.P. 1 ,Kalyuzhnaya Ok.V. 1 , Ravin N.V. 2 , Mardanov A.V. 2 , Beletsky A.V. 2 , Galachyants Yu.P. 1 ,Zemskaya T.I. 1 , Likhoshway Ye.V. 11 Limnological Institute SB RAS, 3, Ulan‐Batorskaya, Irkutsk 664033, Russia,zakharova@lin.irk.ru2 Centre “Bioengineering” RAS, 7, Av. 60‐letiya Octyabrya, Moscow, RussiaIt is important to determine the possible role of bacteria in degradation of diatoms, aswell as the role of factors and participants in the silicon cycle in aquatic ecosystems. The aimof this work was to study associations of bacteria and diatoms in natural objects before theirburial in the sediments and under experimental conditions. The preservation of diatoms inthe surface sediment layer and the amount of bacteria associated with diatom cellsdecreased with depth. The maximal abundance of bacteria associated with diatoms (112thousand bacterial sequences of the 16S rRNA gene fragments) was recorded by means ofpirosequencing in the bottom water layer. The microbial community was represented by thefollowing dominant phylogenetic groups: Proteobacteria, Acidobacteria, Actinobacteria,Cyanobacteria, Bacteroidetes, Verrucomicrobia, Firmicutes, and Nitrospira. However, 32% ofthe sequences appeared to be non‐classified because of the absence of analogues in thedatabase. Seven strains of eubacteria were isolated during cultivation on a medium withdiatom extract. According to the data of microbiological analysis and sequencing of 16SrRNA gene, these strains were identified as Mycoplana bullata, Sphingomonas rhizogenes,Agrobacterium tumefaciens, Bacillus simplex, Acinetobacter johnsonii, Methylobacteriumadhaesivum, and Deinococcus aquaticus. Joint cultivation of these strains with a diatomSynedra acus subsp. radians (Kütz.) Skabitsch. caused inhibition of the diatom growthfollowed by cell destruction. Isolated strains revealed activity of hydrolytic enzymes:protease (B.simplex, M. bullata, and D. aquaticus) of β‐xylosidase, β‐glucosidase, β‐galactosidase, chitobiase (M. bullata, S. rhizogenes, A. tumefaciens, and B. simplex), andamylase (D. aquaticus). The data obtained demonstrate that potential participants in siliconcycle that degrade siliceous valves of diatoms may be present among a great variety ofmicroorganisms in the bottom layer of Lake Baikal.This work was supported by the RAS Presidium Programme “Biosphere Origin andEvolution”, project No. 18.4 and RFBR Gran No. 09‐04‐12231‐ofi‐m.207