Ionofore antibiotic polynactin produced by <i>Streptomyces</i> sp. 156A isolated from Lake Baikal

<p>The potential antibacterial activity of secondary metabolites produced by <i>Streptomyces</i> sp. 156A isolated from Lake Baikal was investigated. The selective liquid–liquid extraction method was applied to obtain a mixture of nactins (polynactin) produced by the strain. The polynactin consisted of nonactin (3%), monactin (18%), dinactin (36%), trinactin (31%) and tetranactin (12%). The compounds were identified by MS/MS, ¹H and ¹³C NMR methods. The loss of neutral 184 and 198 Da fragments from a sodiated molecular ion, [M + Na]⁺, of nactins was observed in the MS/MS spectrum. The polynactin was shown to possess the antibiotic activity against Gram-positive strains including opportunistic strains and strains isolated from various ecosystems of Lake Baikal.</p

The bacteria from the GenBank database most closely related, according to 16S rRNA gene sequences identified from deep near-bottom layer of Lake Baikal.

<p>The bacteria from the GenBank database most closely related, according to 16S rRNA gene sequences identified from deep near-bottom layer of Lake Baikal.</p

Changes in the degree of preservation of diatom frustules in different layers of Lake Baikal bottom sediments.

<p>(A, B) 0–1 cm. (C, D) 2–3 cm. (E, F) 6–7 cm. Scale bars: (A, C, E) 100 µm; (B, D, F) 10 µm.</p

The structure of bacterial community in the near-bottom water layer of Lake Baikal.

<p>Every taxonomic group presented in the dendrogram accounted for no less than 1% of the total number of sequence reads, with the width of branches being proportional to the number of identified reads. Values at the nodes show the number of OTU_0.03 for a given taxon. The diagram at the bottom shows the proportions of OTU_0.03 assigned to taxa of different ranks.</p

Bacterial diversity in the near-bottom water layer of Lake Baikal, as characterized by rarefaction curves of OTUs defined at genetic distance levels of 0.01, 0.03, 0.05, and 0.07.

<p>Bacterial diversity in the near-bottom water layer of Lake Baikal, as characterized by rarefaction curves of OTUs defined at genetic distance levels of 0.01, 0.03, 0.05, and 0.07.</p

Vertical distribution of microorganisms in bottom sediments of Lake Baikal.

<p>(1) Number of diatom-associated bacteria, (2) total number of microorganisms.</p

Bacterial isolates associated with the laboratory culture of <i>S. acus.</i>

<p><i> A. johnsonii</i> BW65UT1570 (A, F), <i>M. adhaesivum</i> BW66UT1570 (B), <i>A. tumefaciens</i> BW62UT1570 (D). The degradated siliceous frustules of diatom <i>S. acus</i> in cocultures with <i>B. simplex</i> BW64UT1570 (C), <i>A. johnsonii</i> BW65UT1570 (E). Axenic culture <i>S. acus</i> (G). Epifluorescent microscopy, DAPI staining (A, B); scanning electron microscopy (D, E, F, G). Scale bar: A, B and G, 50 µm; C, 40 µm; D, 10 µm; E, F, 5 µm.</p

Sample coverage, species richness and species diversity indices.

<p>Sample coverage, species richness and species diversity indices.</p