Improved methods for the cultivation of the chemolithoautotrophic bacterium Nitrosomonas europaea

The chemolithoautotrophic nitrifier Nitrosomonas europaea is useful for biotechnological processes such as bioremediation of toxic chemicals, as well as playing an essential role in the global nitrogen cycle. To successfully apply this bacterium in biotechnology, large quantities of active cells need to be produced. In this paper we demonstrate improved methods for mass cultivation of N. europaea. A doubling in the final cell density to 30 mg dry wt l − 1 was achieved with a fed-batch culture technique using ammonium bicarbonate or sodium bicarbonate for pH control. The cells displayed high ammonia oxidizing activity in excess of 20 mmol g − 1 dry wt h − 1 . Continuous culture under energy limited growth conditions (< 0.1 mM residual ammonium) in a bench scale bioreactor using a microfiltration membrane for high cell recycle produced final culture densities greater than 350 mg dry wt l − 1 . This system allowed operator controlled culturing of cells under excess substrate as well as energy limited growth conditions with a maximum ammonium oxidation potential in excess of 250 mmol g − 1 dry wt h − 1 .