title: Loss of a mycobacterial gene encoding a reductase leads to an altered cell wall containing beta-oxo-mycolic acid analogs and accumulation of ketones.
abstract: Mycolic acids are essential components of the mycobacterial cell wall. In this study, we show that a gene encoding a reductase involved in the final step of mycolic acid biosynthesis can be deleted in Mycobacterium smegmatis without affecting cell viability. Deletion of MSMEG4722 (ortholog of Mycobacterium tuberculosis Rv2509) altered culture characteristics and antibiotic sensitivity. The DeltaMSMEG4722 strain synthesized alpha-alkyl, beta-oxo intermediates of mycolic acids, which were found esterified to cell wall arabinogalactan. While the precursors could not be isolated directly due to their inherent instability during base treatment, their presence was established by prior reduction of the beta-oxo group by sodium borohydride. Interestingly, the mutant also accumulated unsaturated ketones, similar to tuberculenone from M. tuberculosis, which were shunt products derived from spontaneous decarboxylation of alpha-alkyl, beta-oxo fatty acid precursors of mycolic acids.
authors.affiliation: School of Biosciences, University of Birmingham, Edgbaston, Birmingham, UK. a.bhatt@bham.ac.uk
authors.forename: Apoorva
authors.initials: A
authors.lastname: Bhatt
authors.forename: Alistair K
authors.initials: AK
authors.lastname: Brown
authors.forename: Albel
authors.initials: A
authors.lastname: Singh
authors.forename: David E
authors.initials: DE
authors.lastname: Minnikin
authors.forename: Gurdyal S
authors.initials: GS
authors.lastname: Besra
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002473:Cell Wall / Q000201:enzymology* / Q000235:genetics; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D007659:Ketones / Q000378:metabolism*; D050356:Lipid Metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009161:Mycobacterium / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D009171:Mycolic Acids / Q000737:chemistry* / Q000378:metabolism*; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism*; D010957:Plasmids / Q000235:genetics; D012680:Sensitivity and Specificity; D016415:Sequence Alignment; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D000900:Anti-Bacterial Agents; D007659:Ketones; D009171:Mycolic Acids; D010088:Oxidoreductases; C019825:carboxylic acid reductase