Membrane bioreactor for increased production of isoprene gas

A method of producing isoprene, the method comprising:

• (a) culturing cells comprising a heterologous nucleic acid encoding an isoprene synthase polypeptide under suitable culture conditions for the production of isoprene;
• (b) removing a portion of the culture;
• (c) filtering the removed portion of the culture to produce a permeate and a retentate;
• (d) returning the retentate to the culture;
• and
• (e) producing isoprene;
• wherein the cultured cells undergoing steps (b), (c), and (d) either produce isoprene at a higher titer, or have greater average volumetric productivity of isoprene than the same cells cultured without undergoing steps (b), (c), and (d).