Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2005
Publication Date: 6/1/2005
Citation: Zhao, Y., Davis, R.E., Lee, I. 2005. Phylogenetic positions of phytopathogenic mollicutes as inferred from multiple sets of concatenated core house-keeping proteins. International Journal of Systematic and Evolutionary Microbiology. 55:2131-2141.
Interpretive Summary: Plant pathogenic spiroplasmas and phytoplasmas are small, cell wall-less bacteria. These bacteria cause diseases in more than 300 vegetable, ornamental, and perennial species representing over one hundred plant families. Knowledge of evolution of these bacteria should aid in unveiling their lifestyle and their ability to cause diseases. We studied a large group of bacterial proteins that are essential for life. Our results provide a clue to the evolutionary history of these bacteria, which will help us understand how they may have evolved to adapt to their environment and to gain the ability to infect plants. The findings will be of greatest interest to research scientists and students of microbiology and plant pathology.
Technical Abstract: Pyhtopathogenic mollicutes, which include spiroplasmas and phytoplasmas, are cell wall-less bacteria that parasitize plant hosts and insect vectors. Knowledge of evolution of these phytopathogenic agents should aid in unveiling their parasitic lifestyle and pathogenicity. The availability of the first complete phytoplasma and several partial spiroplasma and phytoplasma genome sequences enabled us to investigate the evolutionary relationship between phytopathogenic mollicutes and other micro-organisms, especially gram-positive bacteria, using a comparative genomics approach. Genome data from a total of 41 bacteria species were used for the analysis. Sixty one conserved proteins were selected from each species for construction of a hypothetical phylogenetic tree. Genes of these selected proteins are among a core of genetic elements that constitute a hypothetical minimal genome. These proteins were concatenated into five superproteins according to their functional categories, and phylogenetic trees were reconstructed using distance, parsimony, and likelihood methods. Phylogenetic trees based on the five sets of concatenated proteins are congruent in both clade topology and relative branching length. Spiroplasma kunkelii and phytoplasmas are clustered together with other mollicutes, forming a monophyletic group. Phytoplasmas diverged from spiroplasma and mycoplasmas at early stages of mollicutes evolution. The branch lengths are noticeably longer in the mollicutes clade, suggesting that the genes encoding the six sets of proteins evolved at a greater rate in this clade than in other clades. This observation reinforces the concept that mollicutes may have rapidly evolving genomes.