Membrane lipids of archaea and bacteria.

<p>Archaeal lipids (left) are typically composed of isoprenoid chains linked by ether bonds to an <i>sn</i>-glycerol-1-phosphate (G1P) backbone. The chirality of the two glycerol backbones is fully conserved within each clade not only in structure but in their unrelated synthetic enzymes. Although ether linkages have been observed in bacterial membranes <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001926#pbio.1001926-Lombard1" target="_blank">[15]</a> and isoprenoids are common to all three domains, bacterial lipids (right) are typically composed of fatty acids in ester linkage to an <i>sn</i>-glycerol-3-phosphate (G3P) skeleton. Despite widespread horizontal gene transfer, no bacterium has been observed with the archaeal enantiomer, or vice versa <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.1001926#pbio.1001926-Koga1" target="_blank">[10]</a>.