Pseudomonas putida PCL1760 is a well-studied bacterium that can be used for a wide range of biotechnological applications. In our study we investigated the effect of deletion of the genes involved in alginate accumulation (algA), flagellar export (flhA), and pili formation pilQ on the behavior of the strain in bioreactors. We obtained the knockout mutant P. putida LN6160 with the deletion of these genes and showed that the absence of these genes reduces mobility and biofilm formation (40% lower after 72 h) in the mutant. At the same time, we noted the positive effect of these deletions on the growth of the mutant strain on rich medium (1.39 × 10¹⁰ CFU/mL in the mutant and 6.4 × 10⁹ CFU/mL in the wild type) and on mineral medium (6.11 × 10⁹ CFU/mL in the mutant and 1.36 × 10⁹ CFU/mL in the wild type) by growing them in small-volume bioreactors. A significant decrease in the biofilm and the foam formation was also observed for LN6160 in a small-volume bioreactor. Most probably, the rapid growth of the deletion strain occurs due to a decrease in the energy load on the bacterial apparatus.

Rhizobacteria synthesizing indole-3-acetic acid (IAA) are often used to stimulate plant growth. To enhance IAA production by the rhizospheric bacterium Pseudomonas baetica MGMM504 during the growth on a tryptophan medium, a plasmid encoding naphthalene 1,2-dioxygenase synthesis genes (EC 1.14.12.12) was introduced. The expression of naphthalene 1,2-dioxygenase genes increased IAA synthesis in P. baetica MGMM504(pJeM2:nahA) by 40 % compared with the control. At the same time, P. putida PCL1760(pJeM2:nahA) showed no significant increase in IAA synthesis compared with PCL1760(pJeM2), which produced only trace amounts of IAA. The tests on wheat revealed a higher plant growth stimulating activity of P. baetica MGMM504(pJeM2:nahA), increasing the root length and germination of wheat seedlings by 45 % and 15 %, respectively, compared with P. baetica MGMM504(pJeM2). Neither variant of P. putida PCL1760 exhibited a phytostimulatory effect. The findings suggest that naphthalene 1,2-dioxygenase promotes the formation of an intermediate, which in itself is not a phytostimulator, but can be converted into one if a specialized IAA synthesis system is present in the strain.

Objective: Bacterial biofilms, as a lifestyle strategy for surviving hostile environments, are influenced by their architecture, which is mainly composed of exopolysaccharides. Alginate ensures the structure and biofilm stability, and its biosynthesis is governed by multiple genes, including algA, which encodes enzymes for the alginate precursor. In this study, we evaluated the impact of algA gene deletion on functional biocontrol properties of Pseudomonas putida, including extracellular polymeric substance (EPS), alginate exopolysaccharide production, plant colonization ability, and biocontrol efficacy against Fusarium oxysporum f.sp. radicis-lycopersici (Forl) ZUM2407 in tomato plants. Methods: The extracellular polymeric substance (EPS) was evaluated after precipitation from a 48-h culture grown statically in LB medium covered with cellophane. Alginate content was quantified calorimetrically at 485 nm using a dissolved EPS dissolved in milli-Q water, filtered, and reacted with 80% phenol and H2SO4. The colonization ability was assessed in competitive and non-competitive environments using tomato plants in a gnotobiotic system. The biocontrol efficiency against Forl ZUM2407 was assayed under laboratory conditions. Results: The results obtained demonstrated that algA deletion significantly reduced EPS and alginate production by up to 12.8 ± 1.4% and 5.8 ± 0.2%, respectively. The root colonization ability evaluated in competitive and non-competitive environments demonstrated substantially reduced ability of P. putida PCL1760-ΔalgA, with 69.0 ± 0.4% and 82.5 ± 0.1% decreases in basal and apical tomato part-plants, respectively. Most notably, P. putida PCL1760-ΔalgA was up to 47.01 ± 7.51% less effective in suppressing disease caused by Forl ZUM2407 compared to its wild-type strain, which was up 49.52 ± 8.2% effective. Conclusion: The algA as a critical gene for alginate-mediated biofilm architecture, contributes to root colonization and biocontrol ability in P. putida. These findings extended the critical role for algA in maintaining the plants colonization capacity of PCL1760 and consequent biocontrol performance against Fusarium wilt.

The selection of an optimal antifoam is critical for efficient fermentation, as industrial agents often have detrimental side effects like growth inhibition, while some can enhance productivity. This study presents a rational approach to developing and screening novel silicone-polyol antifoam emulsions. A key finding was the discovery of selective antibacterial activity in agent 3L10, which strongly inhibited Gram-positive bacteria (especially Corynebacterium glutamicum) but not Gram-negative strains. This specificity, likely mediated by interaction with the mycolic acid layer of C. glutamicum, highlights the necessity for strain-specific antifoam testing. A comprehensive evaluation protocol—combining chemical design, cytotoxicity screening across diverse microorganisms, determination of minimum effective concentrations (MEC), and validation in model bioreactor fermentations—was established. Through this process, agent 6T80 was identified as a promising candidate. It exhibited low MEC, high emulsion stability, no cytotoxicity, and did not impair growth or recombinant protein production in B. subtilis or P. putida fermentations. The study concludes that agent 6T80 is suitable for further application in processes involving Gram-negative and certain Gram-positive hosts, whereas agent 3L10 serves as a valuable tool for studying surfactant-membrane interactions. The developed methodology enables the targeted selection of highly efficient and biocompatible antifoams for specific biotechnological processes.

The selection of an optimal antifoam is critical for efficient fermentation, as industrial agents often have detrimental side effects like growth inhibition, while some can enhance productivity. We studied the efficacy of novel silicone–polyol antifoam emulsions for use in fermentation as defoamers. Except for agent 3L10, all antifoams tested did not show inhibition on six bacterial and one fungal culture. Interestingly, agent 3L10 strongly inhibited Gram-positive bacteria (especially Corynebacterium glutamicum) but not Gram-negative strains. A comprehensive evaluation protocol—combining chemical design, cytotoxicity screening across diverse microorganisms, the determination of minimum effective concentrations (MECs), and validation in model bioreactor fermentations—was established. Through this process, 6T80 was identified as a promising antifoam agent for fermentation. It exhibited a low MEC, high emulsion stability, and no cytotoxicity and did not impair growth or recombinant protein production in Bacillus subtilis or Pseudomonas putida fermentations. This study concludes that agent 6T80 is suitable for further application in processes involving Gram-negative and certain Gram-positive hosts. The developed methodology enables the targeted selection of highly efficient and biocompatible antifoams for specific biotechnological processes.