GAPDH gene diversity in spirochetes: a paradigm for genetic promiscuity.

In this study we have determined gap sequences from nine different spirochetes. Phylogenetic analyses of these sequences in the context of all other available eubacterial and a selection of eukaryotic Gap sequences demonstrated that the eubacterial glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene diversity encompasses at least five highly distinct gene families. Within these gene families, spirochetes show an extreme degree of sequence divergence that is probably the result of several lateral gene transfer events between spirochetes and other eubacterial phyla, and early gene duplications in the eubacterial ancestor. A Gap1 sequence from the syphilis spirochete Treponema pallidum has recently been shown to be closely related to GapC sequences from Euglenozoa. Here we demonstrate that several other spirochetal species are part of this cluster, supporting the conclusion that an interkingdom gene transfer from spirochetes to Euglenozoa must have occurred. Furthermore, we provide evidence that the GAPDH genes present in the protists Parabasalia may also be of spirochetal descent.