Nucleic acid relationships among Acholeplasma species

Revised minimal standards for description of new species of the class Mollicutes (division Tenericutes)

Minimal standards for novel species of the class Mollicutes (trivial term, mollicutes), last published in 1995, require revision. The International Committee on Systematics of Prokaryotes Subcommittee on the Taxonomy of Mollicutes proposes herein revised standards that reflect recent advances in molecular systematics and the species concept for prokaryotes. The mandatory requirements are: (i) deposition of the type strain into two recognized culture collections, preferably located in different countries; (ii) deposition of the 16S rRNA gene sequence into a public database, and a phylogenetic analysis of the relationships among the 16S rRNA gene sequences of the novel species and its neighbours; (iii) deposition of antiserum against the type strain into a recognized collection; (iv) demonstration, by using the combination of 16S rRNA gene sequence analyses, serological analyses and supplementary phenotypic data, that the type strain differs significantly from all previously named species; and (v) assignment to an order, a family and a genus in the class, with an appropriate specific epithet. The 16S rRNA gene sequence provides the primary basis for assignment to hierarchical rank, and may also constitute evidence of species novelty, but serological and supplementary phenotypic data must be presented to substantiate this. Serological methods have been documented to be congruent with DNA-DNA hybridization data and with 16S rRNA gene placements. The novel species must be tested serologically to the greatest extent that the investigators deem feasible against all neighbouring species whose 16S rRNA gene sequences show >0.94 similarity. The investigator is responsible for justifying which characters are most meaningful for assignment to the part of the mollicute phylogenetic tree in which a novel species is located, and for providing the means by which novel species can be identified by other investigators. The publication of the description should appear in a journal having wide circulation. If the journal is not the International Journal of Systematic and Evolutionary Microbiology, copies of the publication must be submitted to that journal so that the name may be considered for inclusion in a Validation List as required by the International Code of Bacteriological Nomenclature (the Bacteriological Code). Updated informal descriptions of the class Mollicutes and some of its constituent higher taxa are available as supplementary material in IJSEM Online.

Evidence for the bacterial origin of Acholeplasma laidlawii A

L-forms from a Corynebacterium were induced in hyperosmolar media and gradually adapted to normal osmolarity over a period of two years. During this adaptation several morphologic L-form variants derived from the L-form cultures and were serologically identified as Acholeplasma laidlawii A. The possibility that the bacterial and L-form cultures were contaminated with acholeplasmas was carefully investigated; this was determined not to be the case. Membrane protein gel electrophoresis patterns of these L-form variants were identical to the ATCC A. laidlawii strain PG-8. Acholeplasma phage MVL-1 displayed no affinity for these L-form variants. Phage MVL-2 showed low affinity, but after virus enhancement in the specific host, high plaquing efficiency ensued. DNA hybridization experiments showed a high level of nucleotide sequence homology (greater than 90%) between the L-form-derived variants and PG-8. The homology between the diphtheroid L-forms and the PG-8 strain was 16.4% with te50 values of 86%; this indicates strong base pairing homology. These findings suggest that the L-form variants are acholeplasmas and that they are biologically and genetically related to the Corynebacterium L-forms.

Interspecies and intraspecies DNA homology among established species of Acholeplasma: a review

Radiolabeled DNA probes prepared in vitro by the nick translation method were used to determine the nucleotide sequence homology among the eight established and one unclassified species of Acholeplasma. Very little DNA homology (2 to 21 percent) was found among these nine distinct species and the heteroduplexes showed at least 15 percent mismatching as determined by thermal elution endpoints. The data obtained by hybridization analyses paralleled the results obtained by the growth inhibition and epi-immunofluorescence serologic procedures. The small amount of nucleotide sequence homology among the nine distinct species indicate that the Acholeplasma species are quite distinct and unrelated to each other genomically, findings which should provide useful insight on the molecular biology and evolutionary pathways of these organisms. Labeled 3H-DNA probes to five strains of either A. laidlawii or A. axanthum hybridized to a varying degree to excess amounts of unlabeled DNAs from 12 strains of A. laidlawii and six strains of A. axanthum, respectively. Nucleic acid hybridization analyses showed a wide variation (48 to 100 percent) in DNA homologies among different strains of the two species. The results demonstrate that strains of A. laidlawii and/or A. axanthum isolated from diverse hosts and habitats (birds, rodents, cats, swine, sheep, cattle, horses, goats, primates, and plants) exhibit extensive genotypic variations. 3H-DNA-DNA hybridization procedures were found to be extremely useful in establishing or confirming the existence of distinct species within the genus Acholeplasma.