The B. abortus AidB-YFP is localized at new poles and at constriction sites, in culture and in macrophages. The B. abortus XDB1128 strain was carrying an aidB-yfp fusion on a low copy plasmid, and pdhS-mCherry at the pdhS chromosomal locus. (A) Bacteria were grown in rich medium and the pictures were taken in exponential phase. Differential interference contrast (DIC) is shown on the left. The white arrowheads indicate the dividing cell in which two AidB-YFP foci are detectable. Each scale bar represents 2 μm. The bacterial types are schematically drawn on the right side of the pictures, as they are represented in figure 6. The two upper panels were made with non-diving bacteria, and counting was made with 125 bacteria. The two lower panels were made with dividing bacteria, and counting was made on 84 dividing bacteria. (B) RAW264.7 macrophages were infected for 2, 4, 6, or 24 h with the B. abortus strain expressing aidB-yfp (XDB1120). The infected cells were fixed and immunostained with 12G12 anti-lipopolysaccharide ("α-LPS") primary antibody and anti-mouse secondary antibody coupled to Texas Red. A majority of the bacteria present a single focus of AidB-YFP, suggesting that polar localization of this fusion is also occurring during the infection of macrophages.