Biosynthesis of exopolysaccharides by soil bacteria <i>Paenibacillus mucilaginosus</i> on a nutrient molasses medium

Abstract

Bacterial exopolysaccharides exhibiting water-retaining and cementing properties play an essential role in such processes as the formation and stabilization of soil aggregates, regulation of nutrients and water flow through plant roots, as well as reduction of salt stress in plants. When bacteria producing exopolysaccharides are introduced into a soil, plants become more resistant to water stress due to improved structure and significant accumulation of proline, sugars and free amino acids under the conditions of water deficiency. In this work, we set out to determine the efficiency of exopolysaccharide biosynthesis by the soil bacteria Paenibacillus mucilaginosus when cultivated on a nutrient molasses medium. The bacterial strains P. mucilaginosus 560 and 574 provided by the Departmental collection of non-pathogenic microorganisms for agricultural purposes (All-Russia Research Institute for Agricultural Microbiology, St. Petersburg) were used as exopolysaccharide producers. In order to determine the influence of cultivation conditions on the synthesis of exopolysaccharides by P. mucilaginosus, the one-factor-at-a-time (OFAT) method was used. On the basis of the obtained results, we determined the most effective producer of exopolysaccharides, the age and dose of the inoculum, the optimal values of the cultivation temperature and medium pH, the source of nitrogen and its concentration, as well as the aeration conditions affecting exopolysaccharide biosynthesis and the growth of the selected bacterial strain P. mucilaginosus. It was established that the P. mucilaginosus 574 strain is the most effective producer of exopolysaccharides. It was shown that the biosynthesis of exopolysaccharides is most effective and economical upon the cultivation of P. mucilaginosus 574 on a nutrient medium containing 2% molasses without addition of minerals and nitrogen. The maximum amount of exopolysaccharides can reach 9.55 g/L on a nutrient medium containing 2% molasses at a volume of 50 ml with the addition of 0.1% corn extract as an inducer of exopolysaccharide synthesis at a cultivation temperature of 30±1 °C, a medium pH of 6.0±0.2 with the introduction of 5% inoculum after 24 hours of inoculation. The obtained research results are recommended for use when creating new technologies for the production of microbiological fertilizers.