During the cultivation process different compounds may be fed to the vessel either intermittently or continuously. This allows to maintain optimal environmental conditions in order to maximize сell growth and/or desired product formation. Thus, nutrients, precursors, acid and/or alkali are fed into the medium. The feed rates are manipulated in order to keep certain key variables such as growth rate, respiratory quotient, pH, carbon source concentration at optimum level. Feeding ports are designed to be resterilizable. This allows to connect feeding bottles/vessels to the bioreactor during the operation and to reduce the risk of contamination.