[Conservative motif CMLD in silicic acid transport proteins of diatom algae].

Sequencing of fragments of genes coding for silicic acid transport (SIT) proteins of diatoms of evolutionary distant classes (centric Chaetoceros muelleri Lemmermann, pennate araphid Synedra acus Kützing, pennate raphid Phaeodactylum tricornutum Bohlin, and pennate with keeled raphe system Cylindrotheca fusiformis Reimann et Lewin), revealed the presence in these proteins of a conservative amino acid motif CMLD. Hydropathy profiles suggest that CMLD occupies a position between two transmembrane strands which do not contain lysine and arginine residues. The two strands are good candidates for the role of the channel along which transport of silicic acid occurs. CMLD is a rare motif. Diatoms are known to need Zn2+ for the incorporation of silica. Presumably, CMLD is the site of Zn2+ binding of SITs. We found that the growth of diatoms is inhibited by a negatively charged alkylating reagent 5-(2-iodoacetamidoethyl)aminonaphtalene-1-sulfonic acid which cannot penetrate through the cell membrane. Cysteine of CMLD can be a target of this reagent. Synthetic peptide NCMLDY forms a complex with Zn2+, as revealed by the fact that the ion considerably reduces the rate of alkylation of the peptide.

[The first results of a study of the phylogenetic diversity of microorganisms in southern Baikal sediments from the area of subsurface depositions of methane hydrates].

Phylogenetic analysis of the bacterial communities in Lake Baikal bottom sediments in the region of subsurface methane hydrate depositions has been carried out using data on 16S rRNA sequences. The composition of these microbial communities is shown to be different in different horizons. Methanotrophic bacteria are found in the surface layer (0-5 cm), and uncultured bacteria constitute a great portion of this population. In deeper sediment layers (92-96 cm), achange in the microbial community occurs; specifically, a decreased homology with the known sequences is observed. The new sequences form separate clusters on a phylogenetic tree, indicating the possibly endemic nature of the bacteria revealed. Organisms related to the genus Pseudomonas constitute the main portion of the population. An archaea-related sequence was found in a horizon containing gas hydrate crystals (100-128 cm). Uncultured bacteria remain predominant.