The proposed work is to continue studies of lipid metabolism in diverse bacteria some of which are human pathogens. Although many aspects of bacterial lipid metabolism were first worked out in the paradigm Escherichia coli, other bacteria differ from E. coli in various aspects. A focus will be on the last step of the fatty acid elongatin cycle, the enoyl-ACP reductase reaction, which is catalyzed by a set of very diverse proteins. Since fatty acids are an essential component of bacterial membrane lipids, several of these enzymes are the targets of antimicrobials. A second focus will be on the mechanisms of synthesis of unsaturated fatty acids, an essential component of the membrane lipids of most bacteria. A major puzzle is the mechanism of unsaturated fatty acid synthesis in the Clostridia, which include a number of serious human pathogens. Further investigations of the mechanisms of synthesis of the fatty acid-derived vitamins, biotin and lipoic acid, which are essential enzyme cofactors in all three domains of life, are proposed. Prior work provided the E. coli synthetic pathway in E. coli. However, some bacteria make these cofactors but lack one or more of the proteins used by. Current work is focused on the Firmicutes which include the Bacilli, Clostridia, Staphlococci and thus many important pathogens. In the case of lipoic acid synthesis Bacillus subtilis requires four proteins to synthesize this cofactor whereas E. coli required only two proteins. One of the essential proteins is a key subunit of an enzyme of single carbon metabolism and this interplay will be studied. The early part of biotin synthesis in Bacillus subtilis differs greatly from the pathway used by E. coli and this pathway will be dissected. A third pathway to be studied is that found in the a-proteobacteria (e.g., Brucella) which seems a variation of the E. coli pathway. Study of the mechanisms regulating the synthesis of the various biotin and lipoic acid synthetic pathways will also be done. The E. coli and Bacillus subtilis biotn regulatory systems are quite novel and not fully understood. Further study of these regulatory mechanisms is proposed. Finally, a new class of bacterial quorum sensing molecules the Diffusible Signal Factor (DSF) fatty acids were recently discovered. These are cis-2-enoic acids of medium chain length which trigger breakdown of the biofilms formed by diverse bacteria and some fungi. Prior work demonstrated how the Burkholderia cenocepacia DSF is synthesized, but that enzyme is not fully understood or conserved in some other DSF- producing bacteria. Study of these pathways and mechanisms will use a wide array of genetic, biochemical, molecular biological, chemical and structural approaches.

Public Health Relevance

Fatty acids are an essential component of the bacterial cell envelope and are precursors of two essential vitamins. Studies of how these molecules are made provides targets for discovery of new antibiotics that block these processes resulting in death of the bacteria. Fatty acids are also used to coordinate bacteria to cause infections. !

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
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Prokaryotic Cell and Molecular Biology Study Section (PCMB)
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Korpela, Jukka K
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University of Illinois Urbana-Champaign
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Feng, Youjun; Cronan, John E (2014) PdhR, the pyruvate dehydrogenase repressor, does not regulate lipoic acid synthesis. Res Microbiol 165:429-38
Henke, Sarah K; Cronan, John E (2014) Successful conversion of the Bacillus subtilis BirA Group II biotin protein ligase into a Group I ligase. PLoS One 9:e96757
Bi, Hongkai; Yu, Yonghong; Dong, Huijuan et al. (2014) Xanthomonas campestris?RpfB is a fatty Acyl-CoA ligase required to counteract the thioesterase activity of the RpfF diffusible signal factor (DSF) synthase. Mol Microbiol 93:262-75
Hermes, Fatemah A; Cronan, John E (2014) An NAD synthetic reaction bypasses the lipoate requirement for aerobic growth of Escherichia coli strains blocked in succinate catabolism. Mol Microbiol :
Cronan, John E (2014) The structure of lipoyl synthase, a remarkable enzyme that performs the last step of an extraordinary biosynthetic pathway. Biochem J 464:e1-3
Smith, Alexander C; Cronan, John E (2014) Evidence against translational repression by the carboxyltransferase component of Escherichia coli acetyl coenzyme A carboxylase. J Bacteriol 196:3768-75
Bi, Hongkai; Zhu, Lei; Wang, Haihong et al. (2014) Inefficient translation renders the Enterococcus faecalis fabK enoyl-acyl carrier protein reductase phenotypically cryptic. J Bacteriol 196:170-9
Feng, Youjun; Napier, Brooke A; Manandhar, Miglena et al. (2014) A Francisella virulence factor catalyses an essential reaction of biotin synthesis. Mol Microbiol 91:300-14
Cronan, John E (2013) Improved plasmid-based system for fully regulated off-to-on gene expression in Escherichia coli: application to production of toxic proteins. Plasmid 69:81-9
Feng, Youjun; Xu, Jie; Zhang, Huimin et al. (2013) Brucella BioR regulator defines a complex regulatory mechanism for bacterial biotin metabolism. J Bacteriol 195:3451-67

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