Involved in the biosynthesis of chlorotetracycline (CTC), an important member from antibiotics tetracycline (TC) family, which inhibits protein synthesis in bacteria and is widely involved in clinical therapy, animal feeds and aquaculture. Utilizes FADH(2) supplied by the flavin reductase CtcQ, to catalyze the chlorination of tetracycline (TC) at C7 position, leading to the production of 7-chlorotetracycline. The enzyme forms a lysine chloramine intermediate on an internal lysine residue before transferring the chlorine to the substrate. It is stereo-selective for the 4S (natural) isomer of tetracycline. chloride + FADH2 + O2 + tetracycline = 7-chlorotetracycline + FAD + H(+) + 2 H2O kcat is 0.51 min(-1) for tetracycline (TC) as substrate. Antibiotic biosynthesis. Homodimer. Cells lacking this gene accumulate tetracycline (TC) and abolishe the production of chlorotetracycline (CTC). Belongs to the flavin-dependent halogenase family. Bacterial tryptophan halogenase subfamily.