title: Selection of a biocontrol agent based on a potential mechanism of action: degradation of nicotinic acid, a growth factor essential for Erwinia amylovora.
abstract: This work describes a medium-based screening method for selecting microbial biocontrol agents against Erwinia amylovora based on the degradation of a specific growth factor. Erwinia amylovora, the causal agent of the devastating fire blight disease, requires nicotinic acid or nicotinamide as an essential growth factor. Potential biocontrol agents are either selected for antimicrobial production in plate or directly on immature pears or apple blossoms. In this work, we have attempted to streamline the selection of a new potential biocontrol agent with a lower risk of non-target effects by isolation based on the ability to degrade nicotinic acid in vitro, using therefore few plant materials. A total of 735 bacteria and 1237 yeast were isolated from apple blossoms and pre-screened for nicotinic acid-degradation. Pseudomonas rhizosphaerae strain JAN was able to degrade both nicotinic acid and nicotinamide. Mutants deficient in this ability were constructed. JAN, but not the mutants, controlled E. amylovora on pear slices. On detached apple blossoms, JAN colonized apple hypanthia and strongly suppressed E. amylovora growth. Under greenhouse conditions, JAN was more effective in controlling blossom blight than P. fluorescens A506, a commercial biocontrol agent of fire blight unable to degrade nicotinic acid and nicotinamide.
authors.affiliation: Plant Pathology, Institute of Integrative Biology (IBZ), ETH Zurich, Zurich, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Paternoster
authors.forename: Geneviève
authors.initials: G
authors.lastname: Défago
authors.forename: Brion
authors.initials: B
authors.lastname: Duffy
authors.forename: Cesare
authors.initials: C
authors.lastname: Gessler
authors.forename: Ilaria
authors.initials: I
authors.lastname: Pertot
mesh_terms: D015169:Colony Count, Microbial; D004251:DNA Transposable Elements; D044084:Erwinia amylovora / Q000254:growth & development* / Q000378:metabolism; D035264:Flowers / Q000382:microbiology; D005638:Fruit / Q000382:microbiology; D027845:Malus / Q000382:microbiology; D016254:Mutagenesis, Insertional; D009539:Nicotinic Acids / Q000378:metabolism*; D010802:Phylogeny; D010935:Plant Diseases / Q000382:microbiology / Q000517:prevention & control*; D018520:Plant Shoots / Q000382:microbiology; D011549:Pseudomonas / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D031989:Pyrus / Q000382:microbiology
chemical_list: D004251:DNA Transposable Elements; D009539:Nicotinic Acids