Catalyzes the degradation of citrulline into ornithine, carbon dioxide and ammonia (PubMed:19502406, Ref.3). Contributes to intramacrophage survival, in vivo growth and pathogenesis (PubMed:19502406). 2 H(+) + H2O + L-citrulline = CO2 + L-ornithine + NH4(+) Deletion of the gene results in loss of CTU activity (PubMed:19502406). Loss of the gene does not affect acellular growth, but it impairs intramacrophage survival in resting as well as gamma interferon-stimulated macrophages (PubMed:19502406). Mice infected intranasally with the mutant show significantly reduced bacterial burden in the lungs, liver and spleen compared to wild-type Schu S4-infected mice (PubMed:19502406). Mice infected with the mutant succumb to infection, but they survive longer and show significantly extended median time to death compared to that shown by wild-type Schu S4-infected mice (PubMed:19502406). Is a good candidate for development of an efficient and cost-effective enzymatic-based method for preparation of ornithine. Belongs to the carbon-nitrogen hydrolase superfamily.