Effect of Inactivation of the Bacillibactin Synthase Gene in Bacillus subtilis Strain IV3 on Its Biocontrol Properties

Microorganisms synthesize numerous biologically active compounds that stimulate plant growth and development. In particular, siderophores that eliminate the manifestations of iron deficiency and optimize the associated physiological and biochemical processes in crops in degraded soils. Due to the production of catechol-type siderophores, including bacillibactin, Bacillus strains reduce the risks of phytopathogenic microorganisms and are promising agents of biological plant defense. In this study, the rhizosphere isolate Bacillus subtilis IV3 was characterized as a promising strain with phytoprotective properties. A mutant strain with inactivated bacillibactin biosynthesis gene was obtained from the parental strain B. subtilis IV3 using the CRISPR-Cas9 technology. Comparative characterization of biocontrol properties showed that the native strain synthesized siderophores and IAA, formed dense biofilms, exhibited antagonistic activity against Alternaria sp., F. solani and F. oxysporum, adhered freely and penetrated into the potato root. Loss of the functional dhbF gene resulted in a decrease in the iron assimilation capacity of the strain as well as in a 36.12% decrease in proteolytic activity. Mutation in the dhbF gene affected growth dynamics, reducing biomass yield by 45.7%, and did not affect the antagonistic activity of the strain, biofilm formation, sporulation, adhesion ability, and colonization of potato roots.