The dissertation is devoted to the study of biological properties of the B. amyloliquefaciens subsp. plantarum IMB B-7524 strain and the study of exometabolites that determine its biological activity.
The strain B. amyloliquefaciens subsp. plantarum IMV B-7524 has been isolated from the soil; its antagonistic, elicitor and phyto-stimulating activities and the nature of exometabolites, which determine them, have been investigated. It has been shown that mitigation or elimination of the negative influence of biotic factors of an environment, in particular, phytopathogenic micromycetes, is possible under the conditions of synthesis of the complex of exometabolites of multi-directional action by the strain IMV В-7524 Thus, it has been shown that the strain B.amyloliquefaciens subsp. plantarum ІМВ В-7524 is a promising agent for biocontrol of diseases of agricultural crops caused by phytopathogenic microorganisms.
Based on the results of multi-stage screening of antagonists of actual and collectible phytopathogenic micromycetes and bacteria, 5 strains of bacilli were selected. The strains listed had the highest level and a wide range of antagonistic activity against the specified phytopathogens and the topical pathovars of bacteria of the genus Pseudomonas among the 100 studied strains. In the most cases, antagonistic activity of the selected bacilli strains had the same level, and in certain cases exceeded that of the strain B. amyloliquefaciens IMV B-7100, which is the basis of the known preparation Phytodoctor (Sporophyte). Among these strains, the strain Bacillus sp. С6 was distinguished by indicators of stimulation of growth and development of plants; its metabolites had positive effect on germination and accumulation of biomass in plants of winter wheat roll culture. This property of exometabolites of the strain extends greatly the spectrum of its biological activity and allows us to consider it a promising agent for biocontrol of diseases of agricultural crops.
According to the results of polyphase taxonomic analysis, which included the study of cultural-morphological, physiological-biochemical, chemo-taxonomic and molecular-genetic properties, the selected strain was identified as B. amyloliquefacienssubsp. plantarum ІМВ В-7524. It has been found that the strain B. amyloliquefaciens subsp. plantarum ІМВ В-7524 meets the safety requirements for strains that may be used to create biological preparations for plant growing.
It has been established that in strains of aerobic spore-forming bacteria, selected on basis of the screening results, such as Bacillus sp.С1, С10, Lg24s, Lg37s and B. amyloliquefaciens subsp. plantarum ІМВ В-7524, expression of the genes of synthesis of cyclopepeptide antibiotics of the fengycin family took place. The level of expression of these genes was maximal in the strain IMV В-7524. Besides the genes of fengicynsynthases, transcription of the gene of synthesis of cycloplipopeptides of the iturin family of ituD was also observed in strains IMV B-7524 and Bacillus sp. Lg 37s. It has been shown that exometabolites of the strain B. amyloliquefaciens subsp. plantarum IMV B-7524 includes antibiotic compounds belonging to the fengycin family. Thus, it has been determined that the high antagonistic activity of the selected strain is due to its ability to simultaneously synthesize lipopeptide antibiotics belonging to the families of fengycins and iturins.
The concept of participation of these antibiotics in the manifestation of biocontrol on phytopathogenic micromycetes by the aerobic spore-forming bacteria has been expanded. It has been determined that, when processing young plants of winter wheat with salicylic acid and exometabolites of strain B. amyloliquefaciens subsp. plantarum IMV В-7524, with further infection with the phytopathogenic micromycete B. sorokiniana, a significant reduction of disease development was observed, compared with the control. Since, under the experimental conditions, the treatment with exometabolites of bacilli and conidia of the phytopathogen were separated in space and time, such a result, probably, was achieved not only by the direct fungicidal effect of antibiotics of microbial origin, but also by the stimulation of own self-defense potential of plants. The confirmation of this conclusion is an increase of PAL activity in the roots and shoots of winter wheat plants, because PAL is considered to be a well-known biochemical marker for induction of systemic resistance in plants.
We have investigated the qualitative and quantitative composition of exometabolites that cause the phytostimulating activity of the strain B. amyloliquefaciens subsp. plantarum IMV В-7524. It was established that diluted cultural liquid of the strain stimulates the germination and plant biomass accumulation of winter wheat. It has been shown that the strain synthesizes compounds which belong to 3 classes of hormones–stimulants and a stress hormone abscisic acid.
