Cyanobacterial heterocyst glycolipids in cultures and environmental samples: Diversity and biomarker potential

Abstract

The envelope of cyanobacterial heterocysts contains characteristic glycolipids termed heterocyst glycolipids (HGs). Six cultures of heterocyst‐forming cyanobacteria, as well as samples from 2 polar ecosystems and 12 Spanish freshwaters, were analyzed for their HG content. We tentatively identified four novel HGs in the cyanobacterial strains, including derivatives with a nonhexose sugar moiety. We observed unexpectedly diverse HG distributions in cultures, with very singular fingerprinting for Aphanizomenon aphanizomenoides and Aphanizomenon ovalisporum, thus supporting the taxonomic robustness of HGs. The analysis of HGs in environmental samples revealed even larger diversity and increased abundance of certain HGs that are minor components in cultured strains. Interpretation of HG patterns could be applied to support taxonomic characterization of the community of heterocystous cyanobacteria and to detect changes in the cyanobacterial consortia mediating N2 fixation. In addition to taxonomy, environmental factors seem to influence the biosynthesis of HGs. For example, in our studied environmental samples, temperature appears to influence the relative distribution of keto‐hexacosanol and hexacosanediols, as previously proposed for cultures. Our results extend the knowledge of HG distributions in cyanobacteria and the environment and illustrate the potential of HGs as biomarkers for applications in both ecological and paleoenvironmental studies.