The Mangotoxin Biosynthetic Operon (mbo) Is Specifically Distributed within Pseudomonas syringae Genomospecies 1 and Was Acquired Only Once during Evolution
ABSTRACTMangotoxin production was first described inPseudomonas syringaepv. syringae strains. A phenotypic characterization of 94P. syringaestrains was carried out to determine the genetic evolution of the mangotoxin biosynthetic operon (mbo). We designed a PCR primer pair specific for thembooperon to examine its distribution within theP. syringaecomplex. These primers amplified a 692-bp DNA fragment from 52 mangotoxin-producing strains and from 7 non-mangotoxin-producing strains that harbor thembooperon, whereas 35 non-mangotoxin-producing strains did not yield any amplification. This, together with the analysis of draft genomes, allowed the identification of thembooperon in five pathovars (pathovars aptata, avellanae, japonica, pisi, and syringae), all of which belong to genomospecies 1, suggesting a limited distribution of thembogenes in theP. syringaecomplex. Phylogenetic analyses using partial sequences from housekeeping genes differentiated three groups within genomospecies 1. All of the strains containing thembooperon clustered in groups I and II, whereas those lacking the operon clustered in group III; however, the relative branching order of these three groups is dependent on the genes used to construct the phylogeny. Thembooperon maintains synteny and is inserted in the same genomic location, with high sequence conservation around the insertion point, for all the strains in groups I and II. These data support the idea that thembooperon was acquired horizontally and only once by the ancestor of groups I and II from genomospecies 1 within theP. syringaecomplex.