Phylogenetic analyses of the constituents of Type III protein secretion systems

Lily Nguyen, Ian T. Paulsen, Jason Tchieu, Christoph J. Hueck, Milton H. Saier*

*Corresponding author for this work

Research output: Contribution to journalReview articlepeer-review

89 Citations (Scopus)


Multicomponent Type III protein secretion systems transfer Gram-negative bacterial virulence factors directly from the bacterial cytoplasm to the cytoplasm of a host eukaryotic cell in a process that may involve a single energy-coupled step. Extensive evidence supports the conclusion that the genetic apparatuses that encode these systems have been acquired independently by different Gram-negative bacteria, presumably by lateral transfer. In this paper we conduct phylogenetic analyses of currently sequenced constituents of these systems and their homologues. The results reveal the relative relatedness of these systems and show that they evolved with little or no exchange of contituents between systems. This fact suggests that horizontal transmission of the genes encoding these systems always occurred as a unit without the formation of hybrid gene clusters. Moreover, homologous flagellar proteins show phylogenetic clustering that suggests that the flagellar systems and Type III protein secretory systems diverged from each other following very early duplication of a gene cluster sharing many (but not all) genes. Phylogenies of most or all of the flagellar proteins follow those of the source organisms with little or no lateral gene transfer suggesting that homologous flagellar proteins are true orthologues. We suggest that the flagellar apparatus was the evolutionary precursor of Type III protein secretion systems.

Original languageEnglish
Pages (from-to)125-144
Number of pages20
JournalJournal of Molecular Microbiology and Biotechnology
Issue number2
Publication statusPublished - Apr 2000
Externally publishedYes


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