SIDORENKO M.L., MARTYNENKO E.S.
Agricultural Biology 2026; 61(3): 482-497
In light of the growing awareness of the negative impacts associated with the use of chemical fertilizers, the search for alternative solutions that can reduce the chemical burden on agroecosystems while ensuring the availability of nutrients for plants is becoming increasingly relevant. A promising and environmentally safe approach is the identification of autochthonous microorganisms capable of stimulating plant growth and converting poorly available phosphates into soluble forms. The use of regionally adapted strains ensures their survival and effectiveness under the specific soil and climatic conditions of the target area. Pantoea agglomerans is a widely distributed bacterium of the family Enterobacteriaceae , capable of adapting to diverse environmental conditions and found in soil, water, plants, and air. In the present study, the strain Pantoea agglomerans F19 VKPM-13869, isolated from agricultural soils of Primorsky Krai, was comprehensively characterized for the first time, and a unique set of biologically significant traits relevant to crop production was identified. The strain demonstrated exceptionally high phosphate-solubilizing activity (up to 703 mg/L), with effective phosphorus solubilization maintained at pH 5-6 and moderate salinity (NaCl up to 3 %). A pronounced plant growth-promoting effect on spring wheat and barley was observed. The strain also exhibited 100 % fungicidal and bactericidal activity against the native microflora of cereal seeds. The aim of this study was to investigate the properties of a new перспективного phosphate-solubilizing strain, Pantoea agglomerans F19 VKPM-13869, for agricultural applications. The work was conducted in 2025 at the Core Facility “Biotechnology and Genetic Engineering” of the Federal Scientific Center for Terrestrial Biodiversity of East Asia, Far Eastern Branch of the Russian Academy of Sciences. The strain Pantoea agglomerans F19 (VKPM-13869) was obtained from the All-Russian Collection of Industrial Microorganisms of the National Research Center Kurchatov Institute. It was originally isolated from agricultural soil (agro-dark-humus podbel typical soil, Primorsky Krai, Russia). Cultural and morphological characteristics of the strain were determined on Pikovskaya and GRM agar media using light microscopy. Biochemical properties were assessed using the standardized API 50 CH system (bioMérieux SA, France). Phosphatase activity was determined qualitatively using reagents based on phenolphthalein phosphate and p-nitrophenyl phosphate, while dehydrogenase activity was assessed by the reduction of tetrazolium chloride in semi-solid agar. The production of indole-3-acetic acid was evaluated using the Loper and Schroth method with Salkowski reagent. Qualitative assessment of phosphate-solubilizing activity was carried out on Pikovskaya agar containing insoluble phosphorus sources (Ca3(PO4)2, FePO4, and AlPO4), with calculation of the phosphorus solubilization index (PSI). Quantitative accumulation of soluble phosphorus was determined colorimetrically in liquid Pikovskaya medium on days 3, 5, and 7 of cultivation. The strain’s tolerance to abiotic factors was examined by varying temperature (15-44 °C), pH (from 5 to 9), and NaCl concentration (1-10 %). The plant growth-promoting effect was evaluated based on germination energy and laboratory germination rates of spring wheat (Triticum aestivum L., cultivar Primorskaya 50) and spring barley (Hordeum vulgare L., cultivar Tikhookeansky) after a 30-minute exposure of seeds to a bacterial suspension (10⁷ cells/mL). The fungicidal and bactericidal activity of the strain against native seed microflora was assessed without isolating or identifying specific phytopathogens. Statistical analysis was performed using SPSS v. 11.5, with differences considered significant at p £ 0.05. On Pikovskaya agar, the strain P. agglomerans F19 formed distinct halo zones, while on GRM medium it produced shiny, convex, round yellow colonies. The cells were Gram-negative rods measuring 0.5-1.0 × 1.0-3.0 mm, non-spore-forming, catalase-positive, and oxidase-negative. The strain utilized various carbohydrates (L-arabinose, galactose, xylose, maltose, mannitol, mannose, L-rhamnose, sucrose, and trehalose), fermented glucose with acid production without gas, produced both alkaline and acid phosphatases, exhibited dehydrogenase activity, and synthesized indole-3-acetic acid. High phosphate-solubilizing activity was confirmed: on Pikovskaya medium, the strain formed solubilization zones with diameters of 1.6-2.1 cm for all three insoluble phosphorus sources. The PSI value for tricalcium phosphate reached 5.1±0.1 by day 7. Quantitative analysis revealed soluble phosphorus accumulation ranging from 204 to 703 mg/L by day 7, with a maximum for tricalcium phosphate (603.5±26.7 mg/L). It was established that both growth and phosphorus solubilization were maintained within a pH range of 5-7 and at NaCl concentrations up to 3 %, while at 5 % NaCl growth slowed, and at 10 % it ceased. Treatment of seeds with the bacterial suspension increased germination energy of wheat and barley seeds by 18 % and 20 %, respectively, and laboratory germi-nation rates by 18 % and 16 %. In all experimental variants with treated seeds, 100 % fungicidal and bactericidal activity against native seed microflora was observed. The obtained results indicate a unique combination of agronomically valuable traits in P. agglomerans F19, making it a promising candidate for the development of next-generation microbial products - biofertilizers and biopesticides, particularly for acidic and moderately saline soils of the Russian Far East.
