  We show that in the context of topological string theories N branes and M
anti-branes give rise to Chern-Simons gauge theory with the gauge supergroup
$U(N|M)$. We also identify a deformation of the theory which corresponds to
brane/anti-brane annihilation. Furthermore we show that when $N=M$ all open
string states are BRST trivial in the deformed theory.
