Bioreactor for culturing microorganisms

A bioreactor (1) for culturing microorganisms comprising a reactor vessel (2) which is constructed as a heat exchanger, a plurality of gas-introduction tubes (3) and a gas-introduction system (6) for introducing gas into a culture medium in the gas-introduction tubes (3) via injectors (26), wherein the gas-introduction tubes (3) are connected by their respective lower end (17), in the vertical direction, to the reactor vessel (2) and by their opposite upper end (19) to an upper end (16) of an upright vessel (4) which is likewise connected by its lower end (14) to the reactor vessel (2), and at the upper end (14) of the upright vessel (4) an expansion vessel (5) is arranged, said reactor vessel (2) having a reactor lower part (7) having a biomass chamber (12), and the reactor lower part (7) is covered by an attachment lid (8) which has attachment flanges (18) for the gas-introduction tubes (3), attachment flanges (45) for sensors (28) and an attachment flange (13) for the upright vessel (4).