Biocontainment is an essential feature when deploying genetically modified organisms (GMOs) in open system applications, as variants escaping their intended operating environments could negatively impact ecosystems and human health. To avoid breaches resulting from metabolic cross-feeding, horizontal gene transfer, and/or genetic mutations, synthetic auxotrophs have been engineered to become dependent on exogenously supplied xenobiotics, such as noncanonical amino acids (ncAAs). The incorporation of these abiological building blocks into essential proteins constitutes a first step toward constructing xenobiological barriers between GMOs and their environments. To transition synthetic auxotrophs further away from familiar biology, we demonstrate how bacterial growth can be confined by transition-metal complexes that catalyze the formation of an essential ncAA through new-to-nature reactions. Specifically, using a homogeneous ruthenium complex enabled us to localize bacterial growth on solid media, while heterogeneous palladium nanoparticles could be recycled and deployed up to five consecutive times to ensure the survival of synthetic auxotrophs in liquid cultures.