Bacterial infection often results in the formation of tissue abscesses, which represent the primary site of interaction between invading bacteria and the innate immune system. We identify the host protein calprotectin as a neutrophil-dependent factor expressed inside Staphylococcus aureus abscesses. Neutrophil-derived calprotectin inhibited S. aureus growth through chelation of nutrient Mn2+ and Zn2+: an activity that results in reprogramming of the bacterial transcriptome. The abscesses of mice lacking calprotectin were enriched in metal, and staphylococcal proliferation was enhanced in these metal-rich abscesses. These results demonstrate that calprotectin is a critical factor in the innate immune response to infection and define metal chelation as a strategy for inhibiting microbial growth inside abscessed tissue.

The peripheral membrane ATPase MinD is a component of the Min system responsible for correct placement of the division site in Escherichia coli cells. By rapidly migrating from one cell pole to the other, MinD helps to block unwanted septation events at the poles. MinD is an amphitropic protein that is localized to the membrane in its ATP-bound form. A C-terminal domain essential for membrane localization is predicted to be an amphipathic ␣-helix with hydrophobic residues interacting with lipid acyl chains and cationic residues on the opposite face of the helix interacting with the head groups of anionic phospholipids (Szeto, T. H., Rowland, S. L., Rothfield, L. I., and King, G. F.

The MinCDE proteins help to select cell division sites in normal cylindrical Escherichia coli by oscillating along the long axis, preventing unwanted polar divisions. To determine how the Min system might function in cells with multiple potential division planes, we investigated its role in a round-cell rodA mutant. Round cells lacking MinCDE were viable, but growth, morphology and positioning of cell division sites were abnormal relative to Min+ cells. In round cells with a long axis, such as those undergoing cell division, green fluorescent protein (GFP) fusions to MinD almost always oscillated parallel to the long axis. However, perfect spheres or irregularly shaped cells exhibited MinD movement to and from multiple sites on the cell surface. A MinE-GFP fusion exhibited similar behavior. These results indicate that the Min proteins can potentially localize anywhere in the cell but tend to move a certain maximum distance from their previous assembly site, thus favoring movement along the cell's long axis. A new model for the spatial control of division planes by the Min system in round cells is proposed.

FtsA, a member of the ATPase superfamily that includes actin and bacterial actin homologs, is essential for cell division of Escherichia coli and is recruited to the Z ring. In turn, recruitment of later essential division proteins to the Z ring is dependent on FtsA. In a polar recruitment assay, we found that FtsA can recruit at least two late proteins, FtsI and FtsN, to the cell poles independently of Z rings. Moreover, a unique structural domain of FtsA, subdomain 1c, which is divergent in the other ATPase superfamily members, is sufficient for this recruitment but not required for the ability of FtsA to localize to Z rings. Surprisingly, targeting the 1c subdomain to the Z ring by fusing it to FtsZ could partially suppress a thermosensitive ftsA mutation. These results suggest that subdomain 1c of FtsA is a completely independent functional domain with an important role in interacting with a septation protein subassembly.Cytokinesis in Escherichia coli is a complex process that relies on the intricate timing and placement of the Z ring. FtsZ assembly into the Z ring at mid-cell is proposed to provide a scaffold upon which at least 12 essential cell division proteins, including FtsA, ZipA, FtsEX, FtsK, FtsQ, FtsL, YgbQ, FtsW, FtsI, and FtsN, are recruited in a mostly linear order of dependency (6, 27). The resulting putative protein complex or divisome is required for the synthesis of the division septum and subsequent formation of new cell poles. FtsA, the second protein recruited to the Z ring, is a membrane-associated cytosolic protein (25) that is a member of a large family of ATPases that include actin, Hsp70, sugar kinases, and MreB (4). FtsA localization to mid-cell depends on prior assembly of FtsZ into the Z ring (3, 29) and is mediated via the C terminus of FtsZ (20,32).