Rostislav Alexandrovich Streletsky

Complexes of cultured saprotrophic bacteria and yeasts from different components of soil constructions (humus soil horizon and peat) were studied simultaneously with the assessment of auxin-producing activity (synthesis of 3-indolylacetic acid, IAA), of some bacteria and yeast strains isolated. The study was conducted at the stage of laying two variants of constructions in Syktyvkar, formed from components of local origin (variant 1) and imported (humus soil horizon, Moscow, peat "Seliger-agro", Tver region) (variant 2).

The taxonomic structure of microbial complexes isolated from the studied substrates had significant features of similarity. At the same time, components of variant 1 revealed a greater diversity of cultivated saprotrophic bacteria (Bacillus species) species resistant to adverse environmental conditions as well as the presence of psychrophilic basidiomycete yeast Leucosporidium scottii, which was not found in the components of variant 2.

The average IAA production by the yeast strains studied was 647.6 µg/L and by saprotrophic bacteria - 741.3 µg/L. The highest values of IAA concentration were found in the culture liquid of the yeast Tausonia pullulans (strain Y-6) - 3362.6 µg/l, isolated from the humus soil layer of variant 1, and of the two saprotrophic bacteria Flavobacterium рsychrophilum (strain B-7 - 2616.8 µg/L and B-5 - 1056.3 µg/L), isolated from the humus soil horizon in variant 1 and from peat of variant 2. For strains of the yeast Leucosporidium scottii and the cultured saprotrophic bacteria Flavobacterium psychrophilum the ability to synthesize IAA was found for the first time. 

A laboratory experiment was carried out to investigate the sorption behavior of 2.4-D onto two types of bentonite material: Na-Ca bentonite and organically modified bentonite (HDTMA-Br) using hexadecyltrimethylammonium bromide. The amount of HDTMA-Br was equivalent to the cation exchange capacity of the dominant mineral, montmorillonite, in the bentonites. The results showed that the organically modified bentonite absorbed 4.5 times more 2.4-D compared to the unmodified Na-Ca bentonite, indicating a significantly stronger sorption affinity for the organic cation. This finding suggests that organically modified bentonites may be more effective for the removal of 2.4-D from contaminated soil or water. In the range of pH values between 4 and 6, the sorption sites on the hydrophobic surface of organobentonite were found to have a relatively uniform energy for 2.4-d molecules (Freundlich constant n ≈ 0.8). Hydrophobic interactions were the dominant mechanism for the uptake of 2.4-D at these pH values. The possibility of using HDTMA-bentonite to reduce the mobility of 2.4-D in soils and landscapes, or to create new formulations, should be considered only after a thorough evaluation of the toxic effects of the organoclay on nontarget organisms.