title: Should 'Candidatus Phytoplasma' be retained within the order Acholeplasmatales?
abstract: Phytoplasmas are a diverse but phylogenetically coherent group of cell-wall-less bacteria affiliated with the class Mollicutes. Due to difficulties in establishing axenic culture, phytoplasmas were assigned to a provisional genus, 'Candidatus Phytoplasma', and the genus was embraced within the order Acholeplasmatales. However, phytoplasmas differ significantly from species of the genus Acholeplasma in their habitat specificities, modes of life, metabolic capabilities, genomic architectures, and phylogenetic positions. This communication describes the unique ecological, nutritional, biochemical, genomic and phylogenetic properties that distinguish phytoplasmas from species of the genus Acholeplasma and all other taxa in the class Mollicutes. Since such distinguishing properties of the phytoplasmas are not referable to the descriptions of the order Acholeplasmatales and of all other existing orders, namely Mycoplasmatales, Entomoplasmatales and Anaeroplasmatales, this communication raises the question of whether 'Candidatus Phytoplasma' should be retained in the order Acholeplasmatales or whether a novel provisional order and family should be created to accommodate the genus 'Ca. Phytoplasma'.
authors.affiliation: Molecular Plant Pathology Laboratory, USDA-Agricultural Research Service, Beltsville, MD 20705, USA.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: Molecular Plant Pathology Laboratory, USDA-Agricultural Research Service, Beltsville, MD 20705, USA.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Davis
authors.affiliation: Molecular Plant Pathology Laboratory, USDA-Agricultural Research Service, Beltsville, MD 20705, USA.
authors.forename: Wei
authors.initials: W
authors.lastname: Wei
authors.affiliation: Molecular Plant Pathology Laboratory, USDA-Agricultural Research Service, Beltsville, MD 20705, USA.
authors.forename: Ing-Ming
authors.initials: IM
authors.lastname: Lee
mesh_terms: D004269:DNA, Bacterial / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D045582:Phytoplasma / Q000145:classification* / Q000378:metabolism; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D004269:DNA, Bacterial; D012336:RNA, Ribosomal, 16S