Distribution of long chain heterocyst glycolipids in cultures of the thermophilic cyanobacterium Mastigocladus laminosus and a hot spring microbial mat

摘要

The intact polar lipid (IPL) composition of a microbial mat growing in a sulfidic Icelandic hot spring at 55°C was investigated. The composition was dominated by the glycolipids monoglycosyldiacylglycerol (MGDG), diglycosyldiacylglycerol (DGDG), sulfoquinovosyldiacylglycerol (SQDG) and the glycerophospholipid phosphatidylglycerol (PG). We also detected a series of heterocyst glycolipids (HGs) with an elongated aglycone moiety via comparison with those found in other microbial mats. Based on the mass spectra, we identified the components as 1-(O-hexose)-3,27,29-triacontanetriol (C_(30) HG triol) and 1-(O-hexose)-3,29,31-dotriacontanetriol (C_(32) HG triol). The principal mat builders were the thermophilic heterocystous cyanobacterium Mastigocladus laminosus (Stigonematales) and green nonsulfur-like bacteria (GNSLB) closely related to Chloroflexus aurantiacus. Since HGs are characteristic lipids for heterocystous cyanobacteria, M. laminosus is the likely source of the long chain HGs. IPL analysis of cultivated M. laminosus confirmed that this heterocystous cyanobacterium synthesized the C_(32) HG triol and a related isomer. Culture experiments at different growth temperatures showed no change in the overall HG composition but revealed that the relative proportion of the different C_(32) HG triol isomers varied, possibly as a physiological response to maintaining sub-μM O_2 concentration within the heterocyst. Combined with previous studies, our results suggests that the C_(32) HG triol might be of chemotaxonomic value for identifying heterocystous cyanobacteria of the order Stigonematales in hot spring and other microbial mats.