| Summary: | <p>Abstract</p> <p>Background</p> <p>The original anaerobic unsaturated fatty acid biosynthesis pathway proposed by Goldfine and Bloch was based on in <it>vivo </it>labeling studies in <it>Clostridium butyricum </it>ATCC 6015 (now <it>C. beijerinckii</it>) but to date no dedicated unsaturated fatty acid biosynthetic enzyme has been identified in Clostridia. <it>C. acetobutylicium </it>synthesizes the same species of unsaturated fatty acids as <it>E. coli</it>, but lacks all of the known unsaturated fatty acid synthetic genes identified in <it>E. coli </it>and other bacteria. A possible explanation was that two enzymes of saturated fatty acid synthesis of <it>C. acetobutylicium</it>, FabZ and FabF might also function in the unsaturated arm of the pathway (a FabZ homologue is known to be an unsaturated fatty acid synthetic enzyme in enterococci).</p> <p>Results</p> <p>We report that the FabF homologue located within the fatty acid biosynthetic gene cluster of <it>C. acetobutylicium </it>functions in synthesis of both unsaturated fatty acids and saturated fatty acids. Expression of this protein in <it>E. coli </it>functionally replaced both the FabB and FabF proteins of the host in <it>vivo </it>and replaced <it>E. coli </it>FabB in a defined in <it>vitro </it>fatty acid synthesis system. In contrast the single <it>C. acetobutylicium </it>FabZ homologue, although able to functionally replace <it>E. coli </it>FabZ in <it>vivo </it>and in <it>vitro</it>, was unable to replace FabA, the key dehydratase-isomerase of <it>E. coli </it>unsaturated fatty acid biosynthesis in <it>vivo </it>and lacked isomerase activity in <it>vitro</it>.</p> <p>Conclusion</p> <p>Thus, <it>C. acetobutylicium </it>introduces the double of unsaturated fatty acids by use of a novel and unknown enzyme.</p>
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