The growth of the world's population sets the task of providing people with quality food. Getting a high yield of plants is impossible without the use of fertilizers and plant protection products. However, the use of a large number of chemical compounds leads to their excessive accumulation in plants and can have a negative impact on human health. On the other hand, compounds used for multidirectional treatment of plants partially enter the soil, penetrate into the groundwater, which ultimately affects the quality of natural waters and bottom sediments. Therefore, the primary task is to intensify agricultural production without causing additional damage to the environment. This problem can be partially solved using microorganisms with target properties. For example, microorganisms that increase the bioavailability of nutrients that have phytostimulating properties, have antifungal, insecticidal, acaricidal effects and, at the same time, decompose pesticide residues. Microorganisms that combine several useful traits are especially valuable.
Thphe aim of this work was to search for new microbial strains that are applicable for agricultural production and possess a complex technologically significant potential.
30 strains of soil organisms were isolated from soil samples of the central chernozem region of Russia. The primary selection of strains was performed by direct plating on an agar mineral medium containing sodium benzoate as the only source of carbon and energy. We proceeded from the assumption that the ability to degrade benzoate can serve as a criterion for the presence of a minimum biodegradative potential for two reasons. Despite the relatively simple structure of the benzoate molecule, the biodegradation of this compound presupposes the presence of specialized biodegradation pathways and genes. Bacterial strains capable of degrading benzoate are, to varying degrees, capable of degrading other pollutants. It is important to emphasize that the isolation of soil microorganisms on a mineral medium with benzoate made it possible to quickly assess the presence of one of two biodegradative pathways - ortho- or meta-cleavage of catechol. The data obtained did not allow us to detect strains decomposing benzoate via the pathway of meta-cleavage, since there was no yellow coloration of the medium, characteristic of 2-hydroxymuconic semialdehyde formed as a result of meta-cleavage of catechol, a product of benzoate biodegradation. Thus, it was shown that the metabolism of benzoate in the isolated strains occurs with the induction of catechol 1,2-dioxygenase.
Some of the isolated strains showed high antagonistic activity against fungi-phytopathogens. The new Pseudomonas strain showed high activity. This strain completely inhibited the growth of the fungus Fusarium graminearum, preventing the phytopathogen from developing within a month of co-cultivation. The ability of this strain to inhibit the growth of the bacterial phytopathogen Ralstonia sp. 7-1 should be specially noted. Thus, a number of bacterial strains have been identified that are promising for use in plant protection technologies.
Among the highlighted ones, a new bacterial strain Bacillus sp. This strain is a spore-forming culture and is distinguished by an unusual morphology and development cycle of gram-positive cells. During growth, the strain forms chains of cells of irregular shape, which on the first day of growth on rich nutrient media are filled with multiple lipid granules of unknown nature. Of particular interest is the ability of one of the cells in the chain to divide, forming a helical cell form, which is further split into multiple small irregular cell forms.
Thus, the study of the microbial diversity of chernozems made it possible to identify strains potentially significant for biotechnology, combining such important properties as activity against phytopathogens and decomposition of pollutants, which makes it possible to develop biopreparations for multipurpose purposes. In addition, the isolation of new, previously undescribed bacteria significantly expands the understanding of microbial biodiversity.
The reported study was funded by RFBR according to the research project № 19-54-80003.