GBE Bacterial DNA Sifted from the Trichoplax adhaerens (Animalia: Placozoa) Genome Project Reveals a Putative Rickettsial Endosymbiont Timothy Driscoll1,y, Joseph J. Gillespie1,2,*,y, Eric K. Nordberg1,AbduF.Azad2, and Bruno W. Sobral1,3 1Virginia Bioinformatics Institute at Virginia Polytechnic Institute and State University 2Department of Microbiology and Immunology, University of Maryland School of Medicine 3Present address: Nestle´ Institute of Health Sciences SA, Campus EPFL, Quartier de L’innovation, Lausanne, Switzerland *Corresponding author: E-mail:
[email protected]. yThese authors contributed equally to this work. Accepted: March 1, 2013 Abstract Eukaryotic genome sequencing projects often yield bacterial DNA sequences, data typically considered as microbial contamination. However, these sequences may also indicate either symbiont genes or lateral gene transfer (LGT) to host genomes. These bacterial sequences can provide clues about eukaryote–microbe interactions. Here, we used the genome of the primitive animal Trichoplax adhaerens (Metazoa: Placozoa), which is known to harbor an uncharacterized Gram-negative endosymbiont, to search for the presence of bacterial DNA sequences. Bioinformatic and phylogenomic analyses of extracted data from the genome assembly (181 bacterial coding sequences [CDS]) and trace read archive (16S rDNA) revealed a dominant proteobacterial profile strongly skewed to Rickettsiales (Alphaproteobacteria) genomes. By way of phylogenetic analysis of 16S rDNA and 113 proteins conserved across proteobacterial genomes, as well as identification of 27 rickettsial signature genes, we propose a Rickettsiales endosymbiont of T. adhaerens (RETA). The majority (93%) of the identified bacterial CDS belongs to small scaffolds containing prokaryotic-like genes; however, 12 CDS were identified on large scaffolds comprised of eukaryotic-like genes, suggesting that T.