R-039. A Cluster Analysis of Lipid Component Parts and Selection of Its Combinations Unique to Each Taxon in Archaea

Y. Koga, M. Nakano;
Univ. of Occupational and Environmental Hlth., Kitakyushu, JAPAN.

Membrane polar lipids of Archaea consist of a glycreol backbone with ether-linked isoprenoid chains (core lipid), phosphodiester-linked polar head groups and/or sugar moieties. Core lipids, polar head groups, and monosaccharide units of glycolipids are designated lipid component parts (LCP). Polar lipid composition varies depending on the family or genus to which the archaeal organism belongs. For chemotaxonomic purposes, we developed a simplified analysis of LCP and reported previously. In order to elucidate the relationship of lipid composition and rRNA phylogeny quantitatively we tried two computer-assisted analyses of the LCP distribution pattern among 44 species of euryarchaeal organisms (mainly methanogenic archaea). One is a cluster analysis of the distribution of 20 kinds of LCPs (other than archaeol) performed by the hierarchical grouping method of Ward. The other is a computer-assisted selection of unique hallmark LCP combination that is found exclusively in a given taxon. The cluster analysis revealed that most of the clusters corresponded with the orders and families of Euryarchaeota classified by the rRNA sequence similarity with some exceptions. Members of seven genera of three families of the order Methanomicrobiales have completely the same LCP composition that is so unique that the group was placed the most outside of the other methanoarchaeal orders. The dendrogram revealed the members of Methanosarcinales are more diverse than the other euryarchaeal members. A hypethesis that may explains the reason of the correlation and the discrepancy between the lipid dendrogram and rRNA phylogenetic tree is presented. Unique lipid component parts combinations were selected for most of order, family and genus-level taxa, which are useful for a chemotaxonomic marker. The results confirm and extend the previously reported conclusion based on a more quantitative and convincing basis.