Growth of Bacillus subtilis on citrate and isocitrate is supported by the Mg2+-citrate transporter CitM.
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.
Warner
Jessica B
JB
Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands1.
Lolkema
Juke S
JS
Molecular Microbiology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands1.
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
D001426:Bacterial Proteins; D002352:Carrier Proteins; C102671:CitM protein, Bacillus subtilis; D007523:Isocitrates; D027981:Symporters; D019343:Citric Acid; D009532:Nickel; C034219:isocitric acid