In 1996 we reported the occurrence of lipopolysaccharides (lps), a.k.a. endotoxin, in unicellular, eukaryotic algae (Royce, C. L. and R. L. Pardy. 1996. Endotoxin-like properties of an extract from a symbiotic, eukaryotic Chlorella-like green alga. J. Endotox. Res. 3(6)437-444). This discovery was unprecedented and unanticipated as prevailing microbiology canon teaches that lps molecules are found exclusively in Gram negative bacteria and their cyanobacterial relatives. Thus our findings were greeted with considerable skepticism. Lps is a potent activator of the innate immune system and a major factor in Gram negative sepsis and endotoxic shock. The discovery was made in the context of our ongoing studies of algal endocellular symbiosis. We now hypothesize that algal lps may play an important role in abrogating host phagolysosome processes thus allowing the establishment of hereditary algal symbionts within animal tissue. Subsequent studies revealed that in fact, the algal lps molecules are antagonistic to lps from Gram negative bacteria as analyzed in several animal models. The two recent papers below report on the action of algal lps induction of clotting in the horseshoe crab, a bioassay of immense pharmacological and industrial importance, and report on the occurrence of lipid A in flowering plants. Lipid A is the signature moiety of lps. While the chemical nature of these newly discovered lps awaits description, it is emerging that plants other than algae may possess these interesting and biologically important molecules. Moreover, it has been shown that all genes needed for lipid A synthesis exist in Arabidopsis though there are no reports of the compound in the plant. However, this past year, in work to be presented for publication, we demonstrated the presence of lipid A in Arabidopsis protoplasts. Thus, contrary to the canon asserting that lps is exclusively a Gram negative molecule, it may emerge that these molecules are widespread in plants, perhaps in modified form. The precise role of these plant lps remains to be discovered.
- Conrad ML, Pardy RL, Wainwright N, Child A, Armstrong PB. Response of the blood clotting system of the American horseshoe crab, Limulus polyphemus, to a novel form of lipopolysaccharide from a green alga. Comp Biochem Physiol A Mol Integr Physiol. 2006 Aug;144(4):423-8.
- Armstrong MT, Theg SM, Braun N, Wainwright N, Pardy RL, Armstrong PB. Histochemical evidence for lipid A (endotoxin) in eukaryote chloroplasts. FASEB J. 2006 Oct;20(12):2145-6.