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E. A. FREUNDT ET AL.
diameter, and absence of reversion of fresh isolates to bacteria under
appropriate conditions (Subcommittee on the Taxonomy of Mjrcplasmatales, 1972).
B. Families and genera
Two families are currently recognised in the order Mycoplasmatales.
Family I, the Mycoplasmataceae, includes two genera, Mycoplasma and
Ureaplasma, both of which are distinguished by requiring cholesterol or
other sterols for growth. Associated with this property is their sensitivity
to 1.5% digitonin (Ern0 and Stipkovits, 1973; Freundt et al., 1973a).
The genome size is about 5 x 108 daltons (Bak et al., 1969). Members of the
genus Ureaplasma, previously known as T-mycoplasmas, differ from those
of the genus Mycoplasma in their ability to catabolise urea (Shepard et al.,
1974). Almost all the mycoplasmas of proven pathogenicity to man and
animals are found within the genus Mycoplasma.
Family 11, the Acholeplasmataceae, is characterised by not depending on
sterols for growth and by being resistant to 1’5% digitonin. The genome
size is 1.0 x 109 daltons (Bak et al., 1969). Only one genus, Acholeplmma, is
recognised.
A new genus Anaeroplasma, that will neither fit into Mycoplasmataceae
nor Acholeplasmataceae, because it includes sterol-requiring as well as
sterol-non-requiring organisms, was recently established by Robinson
et al. (1975). Species of this genus are strict anaerobes and have been
isolated hitherto only from the rumens of cattle and sheep.
Recently Skripal (1974) suggested the establishment within the order
Mycoplasmatales of a third family, the Spiroplasmataceae, which was later
accepted by the Subcommittee on Taxonomy of Mycoplasmatales (1977).
The proposed new family, which contains only one genus, Spiroplasma
(Saglio et al., 1973), differs from the two other families in exhibiting helical
morphology and rotational and undulating motility. Sterols are required
for growth, and sensitivity to 1.5% digitonin has been demonstrated.
The genome size is 1.0 x 109 daltons. The discovery in 1973 of the first
member of the new taxon, S. citri, an organism associated with and probably
causing “stubborn disease” of citrus plants, very obviously opened up an
exciting and most promising new field in mycoplasmology. I n addition
to important plant and insect pathogens, the Spiroplasmataceae includes
an organism, the suckling mouse cataract spiroplasma, that is pathogenic
to vertebrates.
Thermoplasma (Darland et al., 1970) is yet another genus that has been
accepted by the Subcommittee for inclusion in the class Mollicutes,
although its allocation to order and family has been postponed until more
E. A. FREUNDT ET AL.
diameter, and absence of reversion of fresh isolates to bacteria under
appropriate conditions (Subcommittee on the Taxonomy of Mjrcplasmatales, 1972).
B. Families and genera
Two families are currently recognised in the order Mycoplasmatales.
Family I, the Mycoplasmataceae, includes two genera, Mycoplasma and
Ureaplasma, both of which are distinguished by requiring cholesterol or
other sterols for growth. Associated with this property is their sensitivity
to 1.5% digitonin (Ern0 and Stipkovits, 1973; Freundt et al., 1973a).
The genome size is about 5 x 108 daltons (Bak et al., 1969). Members of the
genus Ureaplasma, previously known as T-mycoplasmas, differ from those
of the genus Mycoplasma in their ability to catabolise urea (Shepard et al.,
1974). Almost all the mycoplasmas of proven pathogenicity to man and
animals are found within the genus Mycoplasma.
Family 11, the Acholeplasmataceae, is characterised by not depending on
sterols for growth and by being resistant to 1’5% digitonin. The genome
size is 1.0 x 109 daltons (Bak et al., 1969). Only one genus, Acholeplmma, is
recognised.
A new genus Anaeroplasma, that will neither fit into Mycoplasmataceae
nor Acholeplasmataceae, because it includes sterol-requiring as well as
sterol-non-requiring organisms, was recently established by Robinson
et al. (1975). Species of this genus are strict anaerobes and have been
isolated hitherto only from the rumens of cattle and sheep.
Recently Skripal (1974) suggested the establishment within the order
Mycoplasmatales of a third family, the Spiroplasmataceae, which was later
accepted by the Subcommittee on Taxonomy of Mycoplasmatales (1977).
The proposed new family, which contains only one genus, Spiroplasma
(Saglio et al., 1973), differs from the two other families in exhibiting helical
morphology and rotational and undulating motility. Sterols are required
for growth, and sensitivity to 1.5% digitonin has been demonstrated.
The genome size is 1.0 x 109 daltons. The discovery in 1973 of the first
member of the new taxon, S. citri, an organism associated with and probably
causing “stubborn disease” of citrus plants, very obviously opened up an
exciting and most promising new field in mycoplasmology. I n addition
to important plant and insect pathogens, the Spiroplasmataceae includes
an organism, the suckling mouse cataract spiroplasma, that is pathogenic
to vertebrates.
Thermoplasma (Darland et al., 1970) is yet another genus that has been
accepted by the Subcommittee for inclusion in the class Mollicutes,
although its allocation to order and family has been postponed until more