Abstract: A single-use bioreactor, suitable in particular for use in a parallel bioreactor system for applications in cell culture and/or microbiology, a head plate for such a single-use bioreactor and a process for manufacturing the single-use bioreactor and the head plate. The single-use bioreactor comprises a head plate, a dimensionally stable container and a mixer, the head plate and the container enclosing a reaction chamber, and the mixer having a mixer shaft and a stirring member, said mixer shaft being mounted rotatably about a rotational axis in a bearing and the stirring member being fastened torsionally rigidly to the mixer shaft. The mixer and the bearing are arranged entirely within the reaction chamber and the mixer shaft has a magnetic portion which is arranged and adapted in such a way that it can be coupled magnetically in an axial direction to a rotary drive.