Heterocyte glycolipid diketones: A novel type of biomarker in the N2-fixing heterocytous cyanobacterium Microchaete sp.
Résumé
The heterocyte (heterocyst) glycolipid (HG) content of heterocytous (heterocystous) cyanobacteria canprincipally be separated into two different types. In the first type, the aglycone moiety attached to thesugar headgroup exclusively contains hydroxyl functionalities resulting in the formation of HG diolsand HG triols. In the second type, one of the hydroxyl groups is replaced by a ketone functionality givingrise to HG keto-ols and HG keto-diols. In the N2-fixing heterocytous cyanobacterium Microchaetesp. PCC7126 both types of HGs were dominant and consisted primarily of two structural isomers each of theHG28diol and HG28keto-ol. In addition to these well-characterized HGs,Microchaetesp. PCC 7126 alsocontained a yet undescribed type of HG that based on comparison of retention times, molecular weightand mass spectrometry consisted of a hexose headgroup attached to an aglycone moiety with 28 carbonatoms at which two instead of one ketone functionalities were attached. Hence, the novel HG structurewas identified as HG28diketone. This study thus provides further evidence for the large structural diver-sity of HGs, which allows chemotaxonomic profiling of heterocytous cyanobacteria and in turn studyingthe community composition of these important diazotrophs in the geological rock record.