Microbial antagonism of putative bacterial endophytes from apple (Malus × domestica Borkh)

Abstract

It is presumed that all plants are inhabited by diverse species of microorganisms known as endophytes. Information about composition and activity of endophytic microbiome of woody plants is mostly concerned with bacterial and fungal populations of plant rhizosphere. Meanwhile only fragmented knowledge is present about endophytes that reside in phyllosphere of cultivated tree plants such as domestic apple (Malus x domestica Borkh.). In this study, thirty-eight putative endophytic bacterial isolates were cultured from buds of apple. Analysis of 16 S rRNA gene sequence revealed presence of Curtobacterium, Pantoea and six Pseudomonas species among the isolates. Characterization of microbial growth suppresing properties demonstrated that 17, 2, 3 and 4 of the isolates displayed antagonistic activity against Micrococcus luteus, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa, respectively. None of the culture filtrates was inhibiting growth of all four bacteria or Salmonella typhimurium. Ability to produce siderophores was characteristic to 27 of the isolates, and 8 isolates were producers of hydrogen cyanide. However, these traits only weekly correlated to the microbial growth inhibiting properties of sterile culture filtrates prepared from the isolates. Characterization of capability to cross-inhibit growth among the isolates revealed a complex picture of potential interactions that are present within the population of endophytic bacteria of apple phyllosphere. In addition, it was determined that three of endophytic strains were able to inhibit growth of pathogen of apple Venturia inaequalis, suggesting potential for biocontrol application.