| Summary: | <p>Abstract</p> <p>Background</p> <p>The fatty acids of anaerobic ammonium oxidizing (anammox) bacteria contain linearly concatenated cyclobutane moieties, so far unique to biology. These moieties are under high ring strain and are synthesised by a presently unknown biosynthetic pathway.</p> <p>Results</p> <p>Gene clusters encoding enzymes of fatty acid biosynthesis in the anammox bacterium <it>Kuenenia stuttgartiensis </it>and 137 other organisms were analysed and compared <it>in silico </it>to gain further insight into the pathway of (ladderane) fatty acid biosynthesis. In <it>K. stuttgartiensis </it>four large gene clusters encode fatty acid biosynthesis. Next to the regular enzyme complex needed for fatty acid biosynthesis (FASII), the presence of four putative S-adenosyl-methionine (SAM) radical enzymes, two enzymes similar to phytoene desaturases and many divergent paralogues of <it>β</it>-ketoacyl-ACP synthase (<it>fabF</it>) were unusual. Surprisingly, extensive synteny was observed with FASII gene clusters in the deltaproteobacterium <it>Desulfotalea psychrophila</it>. No ladderane lipids were detected in lipid extracts of this organism but we did find unusual polyunsaturated hydrocarbons (PUHC), not detected in <it>K. stuttgartiensis</it>.</p> <p>Conclusion</p> <p>We suggest that the unusual gene clusters of <it>K. stuttgartiensis </it>and <it>D. psychrophila </it>encode a novel pathway for anaerobic PUFA biosynthesis and that <it>K. stuttgartiensis </it>further processes PUFA into ladderane lipids, in similar fashion to the previously proposed route of ladderane lipid biosynthesis. However, the presence of divergent paralogues of <it>fabF </it>with radically different active site topologies may suggest an alternative pathway where ladderane moieties are synthesised externally and are recruited into the pathway of fatty acid biosynthesis.</p> <p>Reviewers</p> <p>This article was reviewed by Dr Michael Galperin (nominated by Prof E. Koonin), Dr Andrei Osterman and Dr Jeremy Selengut.</p>
|
|---|
