Ammonia translocation in cyanobacteria

Abstract

1. SUMMARY Ammonia is the inorganic nitrogen source preferentially used by most cyanobacteria. Moreover, even in nitrate utilizers or N2-fixers, ammonia is an obligate intraeellular intermediate in nitrogen assimilation. It also affects the synthesis and the activation of several key enzymes in nitrogen metabolism such as nitrogenase, ghtamine syn-thetase and nitrate reductase. The mechanism by which NH3/NH~ enters different cyanobacteria (N2-fixers, non.fixers, neutrophilic) was thus studied. Using 14CH3NH~, the convenient radioactive analog of ammonium, we have shown that the neutrophilic A. nidulans R-2 possibly possesses an active transport system for this cation. The conditions leading to repression and depression of this transport system have been studied; it appears that de novo protein synthesis is required for the acquisition of the transport ability. We have also provided evidence that methionine sulfoximine affects ammonium uptake only