Screening Of Genes In Bacillus Velezensis FZB42 Involved In The Colonization Of Fraxinus Mandshurica Root Rhizoplane And The Preliminary Study On Gene Functions

In this study,plant growth promoting rhizobacteria Bacillus velezensis FZB42 and Fraxinus mandshurica were used as the research objects.By identifying the FZB42 colonization sites and the dynamics of colonization in Fraxinus mandshurica,the FZB42 colonization-related genes were screened,and the functions of FZB42 nfrA genes were analyzed.The main results are as follows:(1)FZB42 strain can promote the growth of Fraxinus mandshurica seedlings under high salt conditions.The wild-type FZB42 can colonize the roots of Fraxinus mandshurica stably,and its colonization increases gradually with the growth of host.Epidermal cell surface and intercellular space in the root of Fraxinus mandshurica may be FZB42 preferred colonization sites for green fluorescent labeled strains.(2)Screening of FZB42 transposon-inserted mutant strains AB1,strains with significantly decreased colonization ability in Fraxinus mandshurica root showed a decreasing trend with host growth.Detection of colonization of strain AB1 on the surface of Fraxinus mandshurica,no longer colonized in the form of microcolony aggregation,no obvious biofilm structure was observed,and transposon inserted into gene nfrA in strain AB1.(3)The BB1 of knockout mutant of nfrA gene was successfully constructed by homologous recombination.(4)The colonization ability of knockout mutant strain BB1 on the surface of Fraxinus mandshurica was significantly decreased,and the biofilm formation ability and motility of strain BB1 were not significantly changed compared with wild-type FZB42 strain.The survival rate of strain BB1 under H2O2 stress was significantly lower than that of wild-type strain FZB42,this result showed that the absence of nfrA gene significantly reduced the antioxidant capacity of strain BB1,resulting in its ability to resist host-generated H2O2 during the process of Fraxinus mandshurica colonization,limiting its survival in the root surface environment,resulting in a significant reduction in colonization.Above results will lay a theoretical foundation for revealing the mechanism of B.velezensis FZB42 colonization in Fraxinus mandshurica root.At the same time,it provides theoretical guidance for the development and efficient application of Bacillus sp..