Bacillus megaterium 501 rif introduced into the soil: factors affecting the rate of survival, sporulation and decomposition of the herbicide prometryn

Introduction of microorganisms into the soil is a fundamental problem in application of microbial preparations in agriculture, crop production and ecology. Its effectiveness depends on many factors (i.e. the type and strain of microorganism, the physical and chemical properties of the soil, plant cover, climate and so on), which are not well understood, leading to a high variability of the results of application of microbial preparations. In this article, there is reported the first investigation of survival and sporulation dynamics of Bacillus megaterium 501 rif introduced into sod-podzolic soil, depending on the temperature of the soil, organic matter content and herbicide prometryn, the 2-methylthio-4,6-bis (iso-propylamino)-sim-triazine, application. In laboratory experiments it was found that the optimal conditions for the Bacillus megaterium 501 rif introduced into the soil are achieved at a temperature of 20 °С. After the third day after inoculation the titer of bacteria in the soil increased almost 10 times and remained at that level until the end of the experiment (32 days ). B. megaterium 501 rif throughout the experiment was mainly in the form of a physiologically active cells and fits well into the soil microbiom. Under these conditions an additional incorporation into the soil of the organic matter, such as cereal straw and corn flour, leads to 10-100-fold increase of the amount of B. megaterium 501 rif. At 37 °С the total number of B. megaterium 501 rif reduced several times, and stabilized at this level until the end of the experiment. In this case, 100 % of B. megaterium 501 rif revert into spores and are physiologically inactive. The temperature below the minimum for physiological reproduction of B. megaterium (4 °С) inhibits spore formation and leads to a rapid loss of physiologically active bacterial cells introduced into the soil. The total number of bacteria decreases 1000 times within a month. These data lead to the conclusion that the «low-temperature shock» reduces the competitiveness of B. megaterium to the indigenous microflora and its resistance to bactericidal metabolic products of soil biome. It is shown that at the optimum temperature (20 °С) of soil the B. megaterium inoculation and the use of additional organic matter such as straw accelerate the decomposition of herbicide prometryn, can potentially be used in a biotechnology of remediation of the soil, contaminated by herbicide.