  Renormalized gauge-invariant observables in gauge theories form an algebra
which is obtained as the cohomology of the derivation $[\textbf{Q}_L, -]$ with
$\textbf{Q}_L$ the renormalized interacting quantum BRST charge. For a large
class of gauge theories in Lorentzian globally hyperbolic space-times, we
derive an identity in renormalized perturbation theory which expresses the
commutator $[\textbf{Q}_L, -]$ in terms of a new nilpotent quantum BRST
differential and a new quantum anti-bracket which differ from their classical
counterparts by certain quantum corrections. This identity enables us to prove
different manifestations of gauge symmetry preservation at the quantum level in
a model-independent fashion.
