Inducible lysine decarboxylase that catalyzes the proton-dependent decarboxylation of L-lysine to produce the polyamine cadaverine and carbon dioxide (PubMed:4590109). Plays a role in pH homeostasis by consuming protons and neutralizing the acidic by-products of carbohydrate fermentation (PubMed:17209032). H(+) + L-lysine = cadaverine + CO2 Inhibited by ppGpp, also known as the alarmone. Homodecamer; built of five dimers associated in a 5-fold symmetrical double-ring (PubMed:27080013, PubMed:16301313, PubMed:4590109, PubMed:21278708, PubMed:25097238). Interacts (via C-terminus) with RavA (PubMed:16301313, PubMed:25097238, PubMed:27080013). Part of the cadB-cadA operon, which is under the control of the Pcad promoter (PubMed:16491024). Expression is regulated by CadC (PubMed:1370290, PubMed:8808945, PubMed:16491024). Induction occurs under conditions of low pH with excess lysine and anaerobiosis (PubMed:1370290, PubMed:8808945, PubMed:16491024). The global regulator Lrp has also a positive effect on the expression of the cadBA operon when cells are exposed to moderate acidic stress in the presence of lysine (PubMed:21441513). Repressed by H-NS under non-inducing conditions (PubMed:16491024). Belongs to the Orn/Lys/Arg decarboxylase class-I family.