Gram-negative bacteria, such as Salmonella, use a specialized secretion system (type III) to inject target eukaryotic cells with bacterial effector proteins that subvert the target cell's machinery and promote bacterial virulence. Schlumberger et al.have used time-lapse microscopy to follow in real time the type III injection of mammalian tissue culture cells by Salmonella. They observed the delivery of the bacterial effector protein SipA into the host cytosol using a green fluorescent protein (GFP) fusion to InvB (a binding partner of SipA) to measure the kinetics of arrival. Bacteria were mixed with mammalian cells, and individual bacterium-cell interactions were monitored to see how much SipA remained in the bacterium. After the initial attachment, effector protein was transported into the target cell over the subsequent 1 to 10 min, leaving the bacterium virtually devoid of SipA. The results vividly illustrate the efficiency of the type III secretion system, a key weapon in the establishment of a niche for bacterial multiplication. -- SMH
Proc. Natl. Acad. Sci. U.S.A. 102, 12548 (2005).
