  We study the singular limit of a system of partial differential equations
which is a model for an aggregation of amoebae subjected to three effects:
diffusion, growth and chemotaxis. The limit problem involves motion by mean
curvature together with a nonlocal drift term. We consider rather general
initial data. We prove a generation of interface property and study the motion
of interfaces. We also obtain an optimal estimate of the thickness and the
location of the transition layer that develops.
