No abstract

Site-specific markerless inactivation of genes lysR3 and mtfA of bacteria Pseudomonas brassicacearum S-1 was carried out. It was shown that strains P. brassicacearum S-1-lysR3, P. brassicacearum S-1-mtfA and P. brassicacearum S-1-lysR3-mtfA demonstrate increased antagonistic activity against a number of phytopathogens 1.2–1.6 times higher compared with the original strain. In the laboratory experiment, mutant variants did not affect growth and development of tomato, cucumber and parsley plants. Treating tomato and cucumber seeds with a solution of the culture of the strain P. brassicacearum S-1-lysR3-mtfA led to the increase of seedlings roots length by 1.4 times compared with the original strain. We also determined that the examined strains were able to survive in the soil microbial consortium.

Molecular genetic and functional analysis allowed the identification and characterization of a number of new genetic determinants affecting the synthesis of pyoverdine by P. brassicacearum strain S-1. It was established that inactivation of genes encoding Zn-dependent peptidase (mtfA), peptidase of the C39 (GFU70_09550) family, transmembrane sensor protein (bvgS), heme transporter (ccmC), and protein with unknown function (ydgA) led to changes in fluorescence, efficacy of pyoverdine synthesis and antimicrobial activity in P. brassicacearum strain S-1. A previously undescribed genetic locus that determines the synthesis of pyoverdin was found in the chromosome of the studied bacteria. It was shown that the directed inactivation of this locus led to the complete absence of fluorescence and the production of pyoverdine by P. brassicacearum strain S-1, as well as to the loss of the ability to suppress the growth of the phytopathogenic strain Fusarium oxysporum BIM F-798.