Photoproduction of ammonia from nitrate by Anacystis nidulans cells

Abstract

The addition of some glutamate analogs to illuminated cell suspensions of the cyanobacterium Anacystic nidulans in nitrate-containing medium promoted the release of significant amounts of ammonia. Best results were obtained with micromolar concentrations of the glutamine synthetase inactivator l-methionine- dl-sulfoximine (MSX). Inactivation of cellular glutamine synthetase by MSX was followed by prevention of cell growth and by a significant increase in the rates of uptake and reduction of nitrate. Between 85 and 90% of the ammonia resulting from the photosynthetic reduction of nitrate by the cells was found to accumulate in the outer medium. High rates of ammonia production (25–30 μmol per mg chlorophyll per h) were sustained for longer than 24 h, without interferences of the accumulated ammonia on the process. The MSX-treated cells actively producing ammonia did not appear to suffer of a general nitrogen deficiency, but they rather exhibited a specific deficiency in glutamine and abnormally high levels of carbohydrates. The results indicate the feasibility of using whole cyanobacterial cells for the photoproduction of significant amounts of ammonia from nitrate at the expense of light energy, in a simple version of photobiological energy transduction and storage.