Phenotypic and Molecular-Phylogenetic Analysis Provide Novel Insights into the Diversity of Curtobacterium flaccumfaciens

A multi-phasic approach was used to decipher the phenotypic features, genetic diversity, and phylogenetic position of 46 Curtobacterium spp. strains isolated from dry beans and other annual crops in Iran and Spain. Pathogenicity tests, resistance to arsenic compounds, plasmid profiling and BOX-PCR were performed on the strains. Multilocus sequence analysis (MLSA) was also performed on five housekeeping genes (i.e. atpD, gyrB, ppk, recA, and rpoB) of all the strains, as well as five pathotype strains of the species. Pathogenicity test showed that six out of 42 strains isolated in Iran were non-pathogenic on common bean. Despite no differences found between pathogenic and non-pathogenic strains in their plasmid profiling, the former were resistant to different concentrations of arsenic, while the latter were sensitive to the same concentrations. Strains pathogenic on common bean were polyphyletic with at least two evolutionary lineages (i.e. yellow-pigmented strains vs. red-/orange-pigmented strains). Non-pathogenic strains isolated from solanaceous vegetables were clustered within either the strains of C. flaccumfaciens pv. flaccumfaciens or different pathovars of the species. The results of MLSA and BOX-PCR analysis were similar to each other and both methods were able to discriminate the yellow-pigmented strains from the red-/orange-pigmented strains. A comprehensive study of a worldwide collection representing all five pathovars as well as non-pathogenic strains of C. flaccumfaciens is warranted for a better understanding of the diversity within this phytopathogenic bacterium.