Bacterioneuston in Lake Baikal: Abundance, Spatial and Temporal Distribution.

An aquatic surface microlayer covers more than 70% of the world's surface. Our knowledge about the biology of the surface microlayer of Lake Baikal, the most ancient lake on Earth with a surface area of 31,500 km², is still scarce. The total bacterial abundance, the number of cultured heterotrophic temporal bacteria, and the spatial distribution of bacteria in the surface microlayer and underlying waters of Lake Baikal were studied. For the first time, the chemical composition of the surface microlayer of Lake Baikal was determined. There were significant differences and a direct relationship between the total bacterial abundance in the surface microlayer and underlying waters of Lake Baikal, as well as between the number of cultured heterotrophic bacteria in studied water layers in the period of summer stratification. In the surface microlayer, the share of cultured heterotrophic bacteria was higher than in the underlying waters. The surface microlayer was characterized by enrichment with PO43-, total organic carbon and suspended particulate matter compared to underlying waters. A direct relationship was found between the number of bacteria in the surface microlayer and environmental factors, including temperature, total organic carbon and suspended particulate matter concentration.

Ionofore antibiotic polynactin produced by Streptomyces sp. 156A isolated from Lake Baikal.

The potential antibacterial activity of secondary metabolites produced by Streptomyces 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.