Effect of Selenium–Arabinogalactan Nanocomposite on Environmental Bacteria

It has been previously shown that a selenium (Se) nanocomposite (NC) based on the natural polysaccharide arabinogalactan (AG) produced from Siberian larch wood (Larix sibirica Ledeb.), containing 0.000625% of Se, has antibacterial properties against phytopathogens, such as Clavibacter sepedonicus, Pectobacterium carotovorum, and Phytophthora cactorum. The same concentration of Se/AG NC stimulated the growth and development of potato plants in vitro, as well as the formation of their roots, while Se did not accumulate in potato tissues after plant treatment. However, to realize the full potential of Se/AG NC in agriculture for fighting phytopathogens with the aim of developing commercial nanopreparations, additional toxicological studies are needed to fully address their effects. In this study, to assess the environmental risk of using Se/AG NCs, it was applied to a number of bacteria isolated from soil (Escherichia coli, Bacillus cereus, and B. megaterium), water (Micrococcus luteus, B. subtilis, and Sarcina flava), and activated sludge and wastewater of treatment facilities (Serratia marcescens, M. luteus, B. cereus, and Pseudomonas aeruginosa). When studying the antibacterial activity of Se/AG NC against 11 test cultures of bacteria using the agar diffusion method, it was shown that Se/AG NC had a toxic effect only at high concentrations in the range from 40 mg/mL Se/AG NC (1.68 mg/mL Se) to 0.625 mg/mL Se/AG NC (0.026 mg/mL Se) on two types of bacteria M. luteus isolated from the waters of Lake Baikal and B. cereus obtained from activated sludge of treatment facilities. The maximum diameter of the growth inhibition zone of the test cultures after exposure to different concentrations of Se/AG NC was noted for M. luteus (water) and E. coli (soil) at 40 mg/mL − 26.3 and 20.3 mm, respectively. Thus, the negative impact of Se/AG NC on bacteria from different ecological niches was registered only at high concentrations, similar to the predicted concentrations of Se/AG NC in wastewater, which demonstrates the environmental safety of Se/AG NC for use in agriculture.