title: TCA cycle activity in Staphylococcus aureus is essential for iron-regulated synthesis of staphyloferrin A, but not staphyloferrin B: the benefit of a second citrate synthase.
abstract: Staphylococcus aureus elaborates two citrate-containing siderophores, staphyloferrin A (SA) and staphyloferrin B (SB), that enhance growth under iron-restriction, yet, paradoxically, expression of the TCA cycle citrate synthase, CitZ, is downregulated during iron starvation. Iron starvation does, however, result in expression of SbnG, recently identified as a novel citrate synthase that is encoded from within the iron-regulated SB biosynthetic locus, suggesting an important role for SbnG in staphyloferrin production. We demonstrate that during growth of S. aureus in iron-restricted media containing glucose, SB is produced but, in contrast, SA production is severely repressed; accordingly, SB-deficient mutants grow poorly in these media. Hypothesizing that reduced TCA cycle activity hinders SA production, we show that a citZ mutant is capable of SB synthesis, but not SA synthesis, providing evidence that SbnG does not generate citrate for incorporation into SA. A citZ sbnG mutant synthesizes neither staphyloferrin, is severely compromised for growth in iron-restricted media, and is significantly more impaired for virulence than either of the single-deletion mutants. We propose that SB is the more important of the two siderophores for S. aureus insofar as it is synthesized, and supports iron-restricted growth, without need of TCA cycle activity.
authors.affiliation: Department of Microbiology and Immunology, University of Western Ontario, London, ON, Canada.
authors.forename: Jessica R
authors.initials: JR
authors.lastname: Sheldon
authors.forename: Cristina L
authors.initials: CL
authors.lastname: Marolda
authors.forename: David E
authors.initials: DE
authors.lastname: Heinrichs
mesh_terms: D002950:Citrate (si)-Synthase / Q000378:metabolism*; D002951:Citrates / Q000378:metabolism*; D002952:Citric Acid Cycle; D003470:Culture Media / Q000737:chemistry; D005947:Glucose / Q000378:metabolism; D007501:Iron / Q000378:metabolism*; D009952:Ornithine / Q000031:analogs & derivatives* / Q000378:metabolism; D017262:Siderophores / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000201:enzymology* / Q000254:growth & development / Q000378:metabolism*
chemical_list: D002951:Citrates; D003470:Culture Media; D017262:Siderophores; C083439:staphyloferrin B; C063851:staphyloferrin A; D007501:Iron; D009952:Ornithine; D002950:Citrate (si)-Synthase; D005947:Glucose