Biological Properties of Surface-Active Metabolites of Rhodococcus erythropolis Au-1 and Their Prospects for Crop Technology

Abstract

Background. Trehalose lipids (TLs) are microbial surfactants, they are perspective for using in various industries and agriculture. Investigation of biosurfactants’ properties, as well as mechanisms of their influence on biological objects, is the important task of biotechnology. Objective. The aim of the paper is to study the biological properties of TLs – metabolites of Rhodococcus erythropolis Au-1 – and possible approaches of their using in crop production. Methods. Bacteria were grown on the Goodwin nutrient medium, TLs were extracted from the isolated biomass by the Folch mixture. The influence of test microorganisms on the permeability of cells’ membranes was studied by the release of extracellular protein. The protein content was determined by the Bradford method, the number of viable cells – by the method of serial dilution. Studying of the TLs effect on efficiency of the biocides was carried out on test bacteria by minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the preparations. The influence of the compositions of TLs and biocides on test fungi was evaluated by diameter of inhibition zones in disk susceptibility tests on agar medium. The effect of TLs on the activity of the phytohormone – indolyl 3-acetic acid (IAA) was determined in 2 biotests: on coleoptile stalks of wheat and rhizogenesis of bean seedlings. The influence of metabolites of R. erythropolis Au-1 strain on plant growth was determined in laboratory, vegetative and field experiments. The morphometric indices of wheat and soybean were evaluated after pre-sowing seed treatment. The presence of auxins in the supernatant of R. erythropolis Au-1 was determined with the specific reaction of Salkovsky. Results. It was established that the TLs of R. erythropolis Au-1 strain promote an increase of permeability of cell membranes of phytopathogenic microorganisms (while remaining cell viability). It was shown that TLs enhance antimicrobial activity of biocide-thiosulfonates. The MIC and MBC of biocides in the compositions with trehalose lipids were reduced by 20–50% (for test bacteria), and the diameter of inhibition zones for phytopathogenic fungi increased by an average of 53%. The use of TLs in the IAA composition allows the active concentration of IOC to be reduced by 10 times. In experiments with plants, it has been shown that pre-sowing treatment of seeds with TLs solutions promotes an increase of root and sprout length of the seedlings by 29–37%, and their mass – by 20–31% relative to control. In laboratory conditions it was shown that the supernatant is the most effective preparation: pre-sowing treatment of wheat seed with the supernatant promotes an increase of root and sprout lengths by 58% and 24% respectively. It is established that phytohormones of auxin nature are in the supernatant of R. erythropolis strain. Conclusions. Due to the effect on cell membranes permeability trehalose lipids promote increasing the effectiveness of biocides and plant growth regulators, as well as stimulating plant growth. The obtained results are promising for the development of effective and environmentally friendly products for modern crop production.