Synergistic interaction between Azotobacter and Pseudomonas bacteria in a growth-stimulating consortium

Intensifying agricultural production involves an active use of agrochemicals, which results in disrupted ecological balance and poor product quality. To address this issue, we need to introduce biologized science-intensive technologies. Bacteria belonging to the genera Azotobacter and Pseudomonas have complex growth-stimulating properties and therefore can be used as a bioproduct to increase plant productivity. We aimed to create a growth-stimulating consortium based on the strains of the genera Azotobacter and Pseudomonas, as well as to select optimal cultivation parameters that provide the best synergistic effect. We studied strains Azotobacter chroococcum B-4148, Azotobacter vinelandii B-932, and Pseudomonas chlororaphis subsp. aurantiaca B-548, which were obtained from the National Bioresource Center “All-Russian Collection of Industrial Microorganisms” of Kurchatov Institute. All the test strains solubilized phosphates and produced ACC deaminase. They synthesized 0.98–1.33 mg/mL of gibberellic acid and produced 37.95–49.55% of siderophores. Their nitrogen-fixing capacity ranged from 49.23 to 151.22 μg/mL. The strain had high antagonistic activity against phytopathogens. In particular, A. chroococcum B-4148 and A. vinelandii B-932 inhibited the growth of Fusarium graminearum, Bipolaris sorokiniana, and Erwinia rhapontici, while P. chlororaphis subsp. aurantiaca B-548 exhibited antagonism against F. graminearum and B. sorokiniana. Since all the test strains were biologically compatible, they were used to create several consortia. The greatest synergistic effect was achieved by Consortium No. 6 that contained the strains B-4148, B-932, and B-548 in a ratio of 1:3:1. The optimal nutrient medium for this consortium contained 25.0 g/L of Luria-Bertani medium, 8.0 g/L molasses, 0.1 g/L magnesium sulfate heptahydrate, and 0.01 g/L of aqueous manganese sulfate. The optimal cultivation temperature was 28°C. The microbial consortium created in our study has high potential for application in agricultural practice. Further research will focus on its effect on the growth and development of plants, in particular cereal crops, under in vitro conditions and in field experiments.