About the action of metabolites of plant growth-promoting rhizobacteria Bacillus subtilis on plant salt tolerance (I)

To find out the mode of plant tolerance enhancement against salinity by plant growth-promoting rhizobacteria Bacillus subtilis, metabolites of strains FZB24 and FZB41 were studied in a test system with tomatoes under the influence of high salinity. The culture filtrate (CF) from the fermentative transitional phase, containing the whole range of produced metabolites by B. subtilis, showed to a certain extent tolerance-increasing action at dilution of 0.1% in the test plants with the parameters length, fresh mass and dry mass of shoots and roots as well as leaf area after 7-day treatment and subsequent plant cultivation under high salt stress. Afterwards, the CF was fractionated with adsorber resin and high performance liquid chromatography, and these fractions, as well as fractions from a CF after 19-h fermentation, were also tested with axenic-cultivated tomato seedlings. Fractions with different proteins and peptides, produced by B. subtilis, showed partly activities depending on concentration with regard to plant growth stimulation, including tolerance enhancement against salt stress. Subsequently, also an extract from B. subtilis culture with special concentrated peptides was examined in the axenic plant test system and showed similar activity depending on concentration. The observed effect of the bacterial metabolites is discussed as one part of the mechanism for plant growth stimulation and at the same time salt tolerance, increasing action of the rhizobacterium by its root colonization and interaction with the plant metabolism.