List of the volvocalean strains and their presence or absence of rickettsial endosymbionts examined in this study.

a<p>Microbial Culture Collection at the National Institute for Environmental Studies <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031749#pone.0031749-Kasai1" target="_blank">[24]</a>.</p>b<p>Culture Collection of Algae at the University of Texas at Austin <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031749#pone.0031749-Starr1" target="_blank">[50]</a>.</p>c<p>Determined in this study.</p>d<p>Based on TEM by Nozaki et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031749#pone.0031749-Nozaki4" target="_blank">[22]</a>.</p>e<p>Based on TEM and DAPI-staining by Nozaki et al. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0031749#pone.0031749-Nozaki2" target="_blank">[20]</a>.