Inorganic Nitrogen Control of Growth, Chlorophyll, and Protein Level in Cyanobacterium Nostoc muscorum

Abstract

The level of photosynthetic oxygen evolution, chlorophyll, protein, phycocyanin, nitrate reductase (NR), and glutamine synthetase (GS) was studied in cyanobacterium Nostoc muscorum growing in combined nitrogen free-, NO−3 or NH+4 -medium in order to understand the causes of nitrogen-source-dependent variation in growth. When monitored on the basis of pigment content of culture the growth of Nostoc muscorum was optimal in the presence of NO−3 rather than in the presence of NH+4 or molecular N2. However, on monitering the growth on the basis of cell number, it was evident that both NO−3 or N2-grown-cultures grew at a almost identical rate, while in NH+4 -grown-culture growth was sluggish. The inhibition of photosynthetic O2 evolution by NH+4 appears to limit growth in the latter case. Although both N2 and NO−3 -grown-culture grew at the same rate on the basis of cell number, the NO−3 -grownculture had a higher level of chlorophyll and protein per cell. It is suggested that this accumulation of pigment and reserve protein in NO−3 -grown-culture is due to optimization of photoreduction process of NO−3 by NR coupled with an efficient assimilation of NH+4 by GS. In view of nitrogen-source-dependent variations in pigment and protein level in Nostoc muscorum cells, it is suggested that the cell number is a better parameter to express growth and enzymatic activities in cyanobacteria rather than the pigment level. © 1985, Gustav Fischer Verlag, Stuttgart. All rights reserved.