title: Growth of Bacillus subtilis on citrate and isocitrate is supported by the Mg2+-citrate transporter CitM.
abstract: Bacillus subtilis 168 was assayed for its growth on tricarboxylic acid (TCA) cycle intermediates and related compounds as the sole carbon sources. Growth of the organism was supported by citrate, D-isocitrate, succinate, fumarate and L-malate, whereas no growth was observed in the presence of cis-aconitate,2-oxoglutarate, D-malate, oxaloacetate and tricarballylate. Growth of the organism on the tricarboxylates citrate and D-isocitrate required the presence of functional CitM, an Mg(2+)-citrate transporter, whereas its growth on succinate, fumarate and L-malate appeared to be CitM-independent. Interestingly, the naturally occurring enantiomer D-isocitrate was favoured over L-isocitrate by the organism. Like citrate, D-isocitrate was shown to be an inducer of citM expression in B. subtilis. The addition of 1 mM Mg(2+) to the growth medium improved growth of the organism on both citrate and D-isocitrate, suggesting that D-isocitrate was taken up by CitM in complex with divalent metal ions. Subsequently, the ability of CitM to transport D-isocitrate was demonstrated by competition experiments and by heterologous exchange in right-side-out membrane vesicles prepared from E. coli cells expressing citM. None of the other TCA cycle intermediates and related compounds tested were recognized by CitM. Uptake experiments using radioactive (63)Ni(2+) provided direct evidence that D-isocitrate is transported in complex with divalent metal ions.
authors.affiliation: Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands1.
authors.forename: Jessica B
authors.initials: JB
authors.lastname: Warner
authors.affiliation: Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands1.
authors.forename: Juke S
authors.initials: JS
authors.lastname: Lolkema
mesh_terms: D001412:Bacillus subtilis / Q000254:growth & development* / Q000378:metabolism; D001426:Bacterial Proteins; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D019343:Citric Acid / Q000378:metabolism*; D002952:Citric Acid Cycle / Q000502:physiology*; D007523:Isocitrates / Q000378:metabolism*; D009532:Nickel / Q000378:metabolism; D013379:Substrate Specificity; D027981:Symporters
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C102671:CitM protein, Bacillus subtilis; D007523:Isocitrates; D027981:Symporters; D019343:Citric Acid; D009532:Nickel; C034219:isocitric acid