Construction of the mycoplasma evolutionary tree from 5S rRNA sequence data

Area of Science:

• Microbiology
• Evolutionary Biology
• Genomics

Background:

• The evolutionary origins and phylogenetic relationships of mycoplasmas, a group of bacteria lacking cell walls, remain incompletely understood.
• Understanding mycoplasma phylogeny is crucial for their classification and for insights into bacterial evolution.

Purpose of the Study:

• To construct a phylogenetic tree of eubacteria and mycoplasmas using 5S ribosomal RNA (rRNA) sequences.
• To elucidate the evolutionary history and relationships within the mycoplasma genus.

Main Methods:

• Sequencing of 5S rRNA from various eubacterial and mycoplasma species, including Clostridium innocuum, Acholeplasma, Spiroplasma, Ureaplasma, and Mycoplasma species.
• Phylogenetic analysis of determined and published 5S rRNA sequences.

Main Results:

• Mycoplasmas form a coherent phylogenetic group branching from the low G+C Gram-positive bacteria, near lactobacilli and streptococci.
• The Acholeplasma lineage represents an early branch, with cell wall loss and genome reduction occurring subsequently.
• Further branching led to Spiroplasma and then sterol-requiring mycoplasmas, with multiple independent genome reductions to ~500 MDa in Mycoplasma and Ureaplasma species.

Conclusions:

• Mycoplasma evolution is characterized by early cell wall loss and genome reduction, followed by diversification and independent genome downsizing events.
• Mycoplasmas, especially those with smaller genomes, exhibit high mutation rates, indicating rapid evolution.