Microbial Eukaryotes that Lack Sterols

It is widely held that sterols are key cyclic triterpenoid lipids in eukaryotic cell membranes and are synthesized through oxygen-dependent multi-enzyme pathways. However, there are known exceptions―ciliated protozoans, such as Tetrahymena, along with diverse low-oxygen adapted eukaryotes produce, instead of sterols, the cyclic triterpenoid lipid tetrahymanol that does not require molecular oxygen for its biosynthesis. Here, we report that a number of anaerobic microbial eukaryotes (protists) utilize neither sterols nor tetrahymanol in their membranes. The lack of detectable sterol-like compounds in their membranes may provide an opportunity to reconsider the physiological function of sterols and sterol-like lipids in eukaryotes. This article is protected by copyright. All rights reserved.