4 research outputs found
The Family Acholeplasmataceae (Including Phytoplasmas)The Prokaryotes
The family Acholeplasmataceae was originally established to
accommodate the genus Acholeplasma, comprising the mollicutes that
could be cultivated without the supplement of cholesterol and that
use UGA as a stop codon instead of coding for tryptophan. It was
later shown that the phytoplasmas, a large group of uncultivable,
wall-less, non-helical mollicutes that are associated with plants and
insects, shared taxonomically relevant properties with members of the
genus Acholeplasma. Being not cultivable in vitro in axenic culture, the
phytoplasmas could not be classified using the standards used for other
mollicutes and are named using the category of Candidatus, as “Ca.
Phytoplasma.”
Although phytoplasmas are associated with habitats and ecology
different from acholeplasmas, the two genera Acholeplasma and
“Candidatus Phytoplasma” are phylogenetically related and form a
distinct clade within the Mollicutes. The persisting inability to grow
the phytoplasmas in vitro hinders the identification of their distinctive
phenotypic traits, important criteria for mollicute classification. Until
supplemental phenotypic traits become available, the genus “Candidatus
Phytoplasma” is designated, on the basis of phylogeny, as a tentative
member in the family Acholeplasmataceae. Phylogenetic analysis based
on gene sequences, in particular, ribosomal sequences, has provided
the major supporting evidence for the composition and taxonomic
subdivision of this group of organisms with diverse habitats and ecology
and has become the mainstream for the Acholeplasmataceae systematics.
However, without the ability to determine phenotypic properties, the
circumscription of related species among the non culturable members of
the family remains a major issue.
The genus Acholeplasma comprises 14 species predominantly associated
with animals and isolated from mammalian fluids but regarded as not
normally pathogenic. Conversely, the genus “Ca. Phytoplasma” includes
plant pathogens of major economic relevance worldwide. To date, 36
“Ca. Phytoplasma species” have been described