FIG. 8.

Unrooted phylogenetic tree based on 16S rRNA sequences of thermophilic (thin lines) and hyperthermophilic (thick lines) organisms, highlighting the distribution of DIP (gray circles) and MDIP (boxes) (references 11, 17, and 30 and our unpublished results). The human 18S rRNA sequence was used as an outgroup. The dotted box means that Archaeoglobus profundus possesses the MDIP synthase gene but that the accumulation of MDIP is unknown. The MEGA 4.0 software program (33) was used for sequence alignment and for generation of the phylogenetic tree by use of the neighbor-joining method. Sequences of 16S and 18S rRNA are from the Ribosomal Database Project (http://rdp.cme.msu.edu/hierarchy/hb_intro.jsp).