Effect of light intensity on macromolecular synthesis in cyanobacteria

The light-dependent incorporation of NaH¹⁴CO₃ into low molecular weight compounds, polysaccharide, or protein was determined in cultures of the cyanobacteriumMerismopedia tenuissima incubated at a series of light intensities. There was an inverse relationship between incorporation into polysaccharide and protein. At light intensities of 90 E/m²/sec or above, relative incorporation of radioisotope into polysaccharide was greatest and relative incorporation into protein was lowest. Optimal relative protein accumulation occurred in samples incubated at 20 E/m²/sec. A broader optimum of light intensity for maximal protein accumulation was found if ammonia rather than nitrate was the nitrogen source. Physiological adaptation of cultures to growth at a particular light intensity did not alter the pattern of macromolecular incorporation when those cultures were tested over the series of light intensities. The response of cultures ofOscillatoria rubescens to light intensity was similar to that ofM. tenuissima, although incorporation into low molecular weight compounds was significantly greater.The effect of light intensity on macromolecular synthesis in a natural population ofOscillatoria rubescens was also determined. A pattern similar to that observed in batch cultures ofO. rubescens was occasionally found, but in other experiments there was no increase in relative protein incorporation when light intensity was decreased.