Certain species of Mucorales have been identified as causative agents of mucormycosis, a rare yet often lethal fungal infection. Notably, these fungi exhibit intrinsic resistance to common azole drugs, which target lipids. Given the pivotal role of lipids in drug resistance and their contribution to innate resistance to azoles, this study provides a comprehensive overview of key lipid classes, including sphingolipids (SLs), glycerophospholipids (GPLs), and sterols, in Rhizopus delemar 99-880, a well-characterized reference strain among Mucorales. Using shotgun lipidomics as well as liquid- and gas-chromatography-based mass spectrometric analyses, we identified the lipid intermediates and elucidated the biosynthetic pathways of SLs, PGLs, and sterols. The acidic SLs were not found, probably because the acidic branch of the SL biosynthesis pathway terminates at α-hydroxy phytoceramides, as evident by their high abundance. Intermediates in the neutral SL pathway incorporated higher levels of 16:0 fatty acid compared to other pathogenic fungi. A strikingly high phosphatidylethanolamine (PE)/phosphatdylcholine (PC) ratio was observed among GPLs. Ergosterol remains the major sterol, similar to other fungi, and our analysis confirms the existence of alternate ergosterol biosynthesis pathways. The total lipidomic profile of R. delemar 99-880 offers insights into its lipid metabolism and potential implications for studying pathogenesis and drug resistance mechanisms.
Keywords: amphotericin B; drug resistance; mass spectrometry; mucormycosis; phospholipids; posaconazole; sphingolipids; sterols.