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.

We characterized the cryptic plasmid pM27181 (15,416 bp) isolated from the Stutzerimonas stutzeri strain DIA-8. Sequencing and bioinformatic analysis allowed identification of 20 open reading frames, including genes involved in replication (rep), mobilization (relaxase/mobilization protein), segregation (parA, parG), and site-specific recombination (XerC-like protein), as well as the putative Csr/Rsm regulatory module. Deletion analysis and random ligation yielded three minireplicons: pEBNT-1-K, pEBNT-2, and pEBNT-3. Each contains a replication module comprising a rep gene and an iteron-containing region. All three variants replicated autonomously in both Escherichia coli and Pseudomonas putida. Loss of one of the two iterons in variant pEBNT-3 relative to pEBNT-2 has a host-dependent effect. In P. putida, this deletion increased plasmid copy number, possibly due to attenuation of negative feedback, but reduced segregational stability. In E. coli cells the deletion decreased copy number without a corresponding decrease in segregational stability. pEBNT-1-K retained mobilization activity, whereas no mobilization was detected for pEBNT-2 and pEBNT-3 under the conditions tested, suggesting a reduced risk of horizontal dissemination. These findings suggest that replication control is host-dependent and may involve interaction among the Rep protein, iteron repeats, and intracellular factors. The minireplicons provide a basis for developing genetic tools for pseudomonads and a model for studying plasmid replication in different bacterial hosts.

Bacterial isolates from the samples of Orostachys spinosa (L.) growing in the Baikal region were identified and studied. A total of 16 strains with different morphotypes were obtained, and their generic affiliation was determined by 16S rRNA sequencing. The antagonistic activity was confirmed for most strains belonging to the genus Bacillus. The most pronounced antagonism was exhibited by the strains 117B1–117B5, 117BA, and 117BE, which suggests their possible use as biological control agents against fungal phytopathogens. The ability to synthesize bacterial auxins was expressed in all the studied strains, but at a comparatively low level. The ability to fix atmospheric nitrogen under aerobic conditions was revealed in 14 of the 16 strains. The ability to mobilize phosphorus from calcium salt of phytic acid was found in 11 strains. The highest phosphorus mobilizing activity was observed in representatives of the genus Pseudomonas, particularly in the strains 117B7, 117B9, 117BB, and 117BD. Representatives of the genus Bacillus (the strains 117B1, 117B3, 117B4, 117B5, 117B8, and 117BE) had strong cellulase activity. The greatest ability to degrade cellulose was demonstrated by the strain Bacillus sp. 117BA. The findings indicate that the strains Bacillus sp. 117BA and 117BE and Pseudomonas sp. 117BB and 117BD are promising candidates for the development of new biopreparations.