On culturing Escherichia coli on a mineral salts medium during anaerobic conditions

The substrate and products of the hydrogenlyase complex, formic acid, carbon dioxide, and molecular hydrogen, are co-operatively implicated in maintaining growth of E. coli under anaerobic conditions. Growth is observed in the presence of a combination of carbon dioxide + molecular hydrogen, or carbon dioxide + formic acid in the medium. The study shows that it is possible to culture E. coli under anaerobic conditions while sparging with nitrogen, without supplementing exogenous carbon dioxide, formic acid or molecular hydrogen. This condition occurs when the strain is allowed an appropriate induction period and is present at a sufficiently high cell density, since the cell density affects the rate of e.g. CO₂ production. In a system sparged with nitrogen gas, the removal of CO₂ due to this sparging must be balanced with a cell density dependent production rate of CO₂. It is concluded that the formic hydrogenlyase complex should be considered as an integral part of the general maintenance of the anabolism of E. coli during anaerobic conditions on a mineral salts medium, as well as being a net producer of end products in E. coli metabolism.This work was supported by the Swedish National Board for Industrial and Technical Development. A. Askendahl is acknowledged for valuable assistance in the preparation of figures and P. Warkentin for language editing.