Utilization of amino acids by the blue-green alga Synechococcus AN (Anacystis nidulans)

Abstract

The ability of amino acids to support growth of Synechococcus AN when inorganic nitrogen is lacking was tested. Their relative contribution to growth was greater at low (8 μE∙m−2∙s−1) than at photosynthetically saturating irradiances (150 μE∙m−2∙s−1). At low irradiation growth on most amino acids ranged from 70.4 to 88.9% of growth on NO3 N. In contrast, at saturating irradiances, growth on the same amino acids ranged from only 50.7 to 61.2% of growth on NO3 N. The protein concentration of cells grown on the amino acids ranged from 74.6 to 93.7% of the concentration of NO3 N grown cells. Further, cells grown at low irradiances exhibited relatively higher concentrations of chlorophyll a than cells grown at saturating irradiances. The ecological significance of amino acids appears to be in their nitrogen contribution to the photo-heterotrophic growth of blue-green algae. The enhanced contribution under conditions of low irradiances and limiting inorganic nitrogen would counteract, in part, the effect of low irradiances on photosynthesis possibly enhancing the competitive position of the population.