Sequence analyses of S10-spc operon among 16SrV group phytoplasmas : phylogenetic relationships and identification of discriminating single nucleotide polymorphisms

Phytoplasmas are cell-wall less, uncultivable bacteria, belonging to the class Mollicutes. They parasitise both plant hosts and insect vectors, but knowledge of their biological and molecular properties is limited. In particular, analyses of 16S rDNA nucleotide sequences revealed that 16SrV group phytoplasma strains identified in grapevine plants are closely related, but associated with distinct ecologies. In this work, we investigated the evolutionary relationships of eight representative 16SrV phytoplasma strains by sequencing 15 ribosomal protein (rp) genes positioned within the S10-spc operon. Phylogenetic analyses of concatenated nucleotide and amino acid sequences underscored that 16SrV phytoplasma strains infecting grapevine clustered together in a distinct clade, supporting the hypothesis that they have a probable common origin. Furthermore, sequence typing revealed the presence of single nucleotide polymorphisms distinguishing the analysed 16SrV phytoplasma strains. Moreover, rp gene nucleotide sequences could help the description and the accurate definition of 'Candidatus' species within the 16SrV group.