Steady state and dynamic behavior of continuous mixed cultures of two cell species with commensalistic interaction and kinetic feedback is investigated. The generation of the substrate required for growth of the host cell species from a primary resource is catalyzed by extracellular enzymes produced by the cell species, providing thereby, a kinetic feedback. The steady states are divided into three types. For the form of kinetics considered, the reactor can operate at up to seven steady states, including up to four steady states in which the cell species coexist. Conditions for admissibility and stability of different steady states are derived analytically. Admissibility of cyclic states is investigated. The specific example considered pertains to anaerobic digestion of complex insoluble organics by acid generating and methane generating bacteria. For a specific kinetic parameter set, the operating parameter space is divided into multiple regions based on admissibility of various steady states and dynamic characteristics. Startup policies to reach desired steady states are discussed. (c) 2006 American Institute of Chemical Engineers.