| STUDY | Lipids containing a ladderane--a chain of fused cyclobutane rings--make up the bulk of dense membranes in certain unusual bacteria. Jaap S. Sinninghe Damsté of the Royal Netherlands Institute for Sea Research and coworkers discovered the compounds in anammox bacteria, which anaerobically oxidize ammonia to dinitrogen [Nature, 419, 708 (2002)]. The staircaselike motif of cis-fused cyclobutanes has never before been seen in nature. The most abundant lipid in the bacteria is the methyl ester of a C20 fatty acid with five fused rings (shown). Other lipids contain three fused cyclobutane rings attached to a cyclohexane. Both ladderane moieties occur in alcohols and glycerol ethers as well as in fatty acids. The lipids are found in a membrane that surrounds the compartment within the bacterial cell where ammonia is oxidized. Their presence makes the membrane exceptionally dense and resistant to diffusion, helping to contain toxic intermediates such as hydrazine and hydroxylamine, the researchers suggest |
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