Acholeplasma multilocale sp. nov., isolated from a horse and a rabbit

Genome analysis-based union of the genus Mesoplasma with the genus Entomoplasma

Early characterization of strains designated into the genera Entomoplasma and Mesoplasma was based upon biological and chemical characteristics. With the advent of 16S rRNA gene sequence analysis as an added taxonomic character, it became clear that the two genera did not form distinct and separate monophyletic clusters. A genome-level analysis of all 17 validly published species within the family Entomoplasmataceae has recently been performed. Phylogenetic analyses, comparisons of gene content, and the lack of genus-specific genes supported that species from the two genera are intermixed and should not be taxonomically separated. This level of analysis clearly reveals the necessity to revise the taxonomy of this family by merging the two genera into one, Entomoplasma. Additionally, it was definitively determined that the strain originally designated as Acholeplasma multilocale resides in this cluster and should be formally renamed as Entomoplasma multilocale. Merging Mesoplasma and Entomoplasma yields a paraphyletic genus, but is supported by cell morphology and ecology to be distinguished from the genera Spiroplasma and Mycoplasma.

Convergent Evolution among Ruminant-Pathogenic Mycoplasma Involved Extensive Gene Content Changes

Convergent evolution, a process by which organisms evolved independently to have similar traits, provides opportunities to understand adaptation. The bacterial genus Mycoplasma contains multiple species that evolved independently to become ruminant pathogens, which represents an interesting study system for investigating the process. In this work, we determined the genome sequences of 11 Entomoplasma/Mesoplasma species. This new data set, together with the other available Mollicutes genomes, provided comprehensive taxon sampling for inferring the gene content evolution that led to the emergence of Mycoplasma Mycoides cluster. Our results indicated that the most recent common ancestor (MRCA) of the Mycoides-Entomoplasmataceae clade lost ∼15% of the core genes when it diverged from the Spiroplasma Apis clade. After this initial wave of genome reduction, relatively few gene gains or losses were inferred until the emergence of the Mycoides cluster. Compared with those Entomoplasmataceae lineages that maintained the association with insects, the MRCA of the Mycoides cluster experienced a second wave of gene losses, as well as acquiring >100 novel genes through horizontal gene transfer. These gene acquisitions involved many with the Mycoplasma Hominis/Pneumoniae lineages as the putative donors, suggesting that gene exchanges among these vertebrate symbionts with distinct phylogenetic affiliations may be important in the emergence of the Mycoides cluster. These findings demonstrated that the gene content of bacterial genomes could be exceedingly dynamic, even for those symbionts with highly reduced genomes. Moreover, the emergence of novel pathogens may involve extensive remodeling of gene content, rather than acquisition of few virulence genes.

Genetic analysis of housekeeping genes of members of the genus Acholeplasma: Phylogeny and complementary molecular markers to the 16S rRNA gene

The partial nucleotide sequences of the rpoB and gyrB genes as well as the complete sequence of the 16S-23S rRNA intergenic transcribed spacer (ITS) were determined for all known Acholeplasma species. The same genes of Mesoplasma and Entomoplasma species were also sequenced and used to infer phylogenetic relationships among the species within the orders Entomoplasmatales and Acholeplasmatales. The comparison of the ITS, rpoB, and gyrB phylogenetic trees with the 16S rRNA phylogenetic tree revealed a similar branch topology suggesting that the ITS, rpoB, and gyrB could be useful complementary phylogenetic markers for investigation of evolutionary relationships among Acholeplasma species. Thus, the multilocus phylogenetic analysis of Acholeplasma multilocale sequence data (ATCC 49900 (T) = PN525 (NCTC 11723)) strongly indicated that this organism is most closely related to the genera Mesoplasma and Entomoplasma (family Entomoplasmataceae) and form the branch with Mesoplasma seiffertii, Mesoplasma syrphidae, and Mesoplasma photuris. The closest genetic relatedness of this species to the order Entomoplasmatales was additionally supported by the finding that A. multilocale uses UGA as the tryptophan codon in its gyrB and gyrA sequences. Use of the UGA codon for encoding tryptophan was previously reported as a unique genetic feature of Entomoplasmatales and Mycoplasmatales but not of Acholeplasmatales. These data, as well as previously published data on metabolic features of A. multilocale, leads to the proposal to reclassify A. multilocale as a member of the family Entomoplasmataceae.