Vol 54, No 8 (2018)

The review covers the strategies for the biodegradation of a dangerous pollutant of the environment, an explosive 2,4,6-trinitrotoluene. The characteristics of the metabolism of this compound in microorganisms under aerobic and anaerobic conditions and the main enzymes involved in the transformation are described. The main class of enzymes involved in the destruction of trinitrotoluene are nitroreductases; oxidases, hydrogenases, and peroxidases may also be involved in degradation. Several approaches to the biodegradation of trinitrotoluene in the environment have been singled out and discussed: bioaugmentation of the biomass of TNT-destructor strains and consortia of microorganisms that degrade this compound; stimulation of the autochthonous microflora of polluted natural environments via the introduction of additional substrates for microorganism growth and electron donors for the reduction of trinitrotoluene; pollutant biodegradation by immobilized cells of microorganisms in bioreactors and biofilters; phytoremediation and the application of preventive measures consisting of the introduction of spores and lyophilisates of bacteria with biodegradation activity in a mixture containing nitroaromatic compounds.

The method for the biosynthesis of silver sulfide nanoparticles using a strain of Shewanella oneidensis MR-1 in an aqueous solution of silver nitrate and sodium thiosulfate salts has been optimized. Optimization is associated with the biosynthesis of nanoparticles directly in the culture medium in the presence of live cells, which increases the nanoparticle yield by 15–20% and significantly shortens the entire process of obtaining nanoparticles. It was also shown that an increase in the concentration of sodium thiosulfate and silver nitrate salts from 1 mM to 10 mM increases the nanoparticle concentration in the reaction solution, whereas the nanoparticle yield in terms of the silver introduced in the reaction decreases. The nanoparticles obtained by the optimized and the conventional methods do not differ in shape, size, and chemical composition. It was shown that the efficiency of nanoparticle biosynthesis depends on the composition of the liquid nutrient medium for S. oneidensis MR-1 cell growth. Cell culturing in nutrient medium for over 24 h fails to intensify the biosynthesis process.

The screening of aqueous extracts of herbaceous plants that grow on the territory of the Russian Federation with their subsequent use for the biosynthesis of silver nanoparticles (SNPs) in accordance with the principles of green chemistry has been performed. Extracts from the leaves of three plants (Mentha piperita L., Melilotus officinalis, and Archangelica officinalis) promoted efficient synthesis of SNPs, reducing the silver cation from AgNO₃. SNP formation was tested on a spectrophotometer. Atomic force microscopy showed that plant extracts cause the formation of SNPs of different sizes—from 10 to 80 nm. Scanning electron microscopy revealed SNPs with various shapes and sizes; they were most commonly spherical. The obtained nanoparticles had a bactericidal effect on Escherichia coli K-12 and Pseudomonas aeruginosa PA01 (the latter being more resistant), and they suppressed the formation of E. coli biofilms. The obtained data show that the use of extracts from three herbaceous plants provides a readily available and ecologically safe method for the production of SNPs with antimicrobial activity.