Abstract
Minute 3. Report of the Chairman.
J. M. Bradbury thanked Drs R. Rosengarten, G. Stanek, C. Citti and the organizing committee of the 14th International Congress of the IOM for their assistance in making arrangements and for providing accommodation for the subcommittee meetings.
It was recorded with great regret that Dr Roger Miles had passed away on 25 October 2001. His contributions to subcommittee business since 1994 were much appreciated. The resignation of Dr F. Laigret was also recorded and his involvement with the subcommittee since 1992 was gratefully acknowledged.
The subcommittee was very pleased to congratulate Dr J. G. Tully on the award of the prestigious Bergey medal in recognition of his lifelong contributions in the field of systematic bacteriology.
Several novel species in the class Mollicutes were described in the previous biennium. These included Mycoplasma agassizii, Mycoplasma alligatoris and Mycoplasma microti, which were isolated from the desert tortoise, the American alligator and the prairie vole, respectively. Some organisms were also transferred into the genus Mycoplasma from other genera: Mycoplasma haemofelis, Mycoplasma haemomuris, Mycoplasma suis and Mycoplasma haemocanis were transferred from the genus Haemobartonella and Mycoplasma wenyonii from the genus Eperythrozoon. Three novel Candidatus Mycoplasma species were described. These were Candidatus Mycoplasma haemodidelphidis' from the opossum, Candidatus Mycoplasma haemolamae from the alpaca and Candidatus Mycoplasma heamominutum from the cat. Ureaplasma parvum was split off from Ureaplasma urealyticum as a separate novel species and there was a novel Candidatus Phytoplasma species, Candidatus Phytoplasma brasiliense.
Minute 4. Spiroplasma taxonomy.
R. F. Whitcomb summarized recent work on the phylogeny and taxonomy of spiroplasmas and other mollicutes that included serology, 16S rRNA gene sequencing, phylogeny and the acquisition of 16 candidate novel species from tabanids (horseflies) collected in Costa Rica and Australia.
Phylogenetic trees constructed by using maximum-parsimony (the preferred method), maximum-likelihood or distance-matrix-based methods gave trees with similar topologies. Serology had been fundamental in the establishment of the existing spiroplasma species and groups. More than 5000 serological cross-tests were carried out and none disagreed with the phylogenetic trees. In terms of host association, the spiroplasmas from horseflies fell into two groups, which were earlier judged as short or long in morphology. Members of the former group grow to 1011 colony-forming units (c.f.u.) in culture, are easily filterable, utilize arginine, and the G+C content of their DNA is high (2931 mol%). Although the second group of horsefly spiroplasmas is technically not monophyletic, its members occupy a group of closely related clades of the apis group. The G+C content of the DNA of members of this clade set is 26 mol%, the members' cells are very long, grow to 1010 c.f.u. in culture and glucose, but not arginine, is utilized. These two groups appear as clades in the overall tree. The research group has compiled the polyphasic classification using all the available information on G+C content, genome size, serology, sterol requirement, glucose utilization etc. This approach permits an organism to be classified in the absence of a 16S rRNA gene sequence.
Serological methods for identification of spiroplasmas were regarded as highly appropriate, especially when used in conjunction with 16S rRNA gene sequence analysis. These tests are less cumbersome than the DNADNA reassociation method. Furthermore, serology operates at the same level of taxonomic resolution as DNADNA reassociation. Availability of antisera, although not currently a problem, could become one in the future. At this point, antisera to all existing species, groups, and candidate species and/or groups are available.
Minute 5. Phytoplasma taxonomy.
G. Firrao reported on phylogeny and taxonomy of phytoplasmas. Classification of phytoplasmas will in the near future be based on polyphasic taxonomy. In a paper on the aster yellows cluster of phytoplasmas, classification was based on sequence comparisons of the 16S rRNA genes and the tuf genes [Marcone et al., Int J Syst Evol Microbiol 50 (2000), 17031713]. By this approach, the number of groups was reduced, although it may not be applicable to all phytoplasmas. A short manuscript on the genus Candidatus Phytoplasma was in preparation in which the essential properties of this Candidatus genus are described. A list of species will probably also be included. The proposed classification will be based on results already published and an alignment of all 16S rRNA gene sequences currently available for phytoplasmas (about 150) will be provided. About 30 Candidatus Phytoplasma species will be described, based on a cut-off level of 97.5 % sequence similarity of the 16S rRNA genes.
The difficulties associated with defining a type for a Candidatus genus were discussed and another concern was that authors who determined the 16S rRNA gene sequences of a particular Candidatus Phytoplasma species might not necessarily be involved in naming the species, thus denying them some credit for their work. It was suggested that a series of short papers defining the various novel species should be published in association with the paper on the genus Candidatus Phytoplasma.