Abstract
Cyanobacteria are representative photoautotrophic organisms, which must regulate metabolic activities on various pathways under fluctuant environments. To investigate responses to nutrient starvation, we quantified amino acids, which are located at the center of carbon, nitrogen and sulfur metabolism, with gas chromatography - mass spectrometry and analyzed free amino acids pool of Synechocystis sp. PCC 6803 under nitrogen starvation. Unexpectedly, most of proteinogenic amino acids increased temporary in 24 h after transfer to nitrogen poor condition. More remarkably tyrosine and lysine accumulated compared to other amino acids. These two amino acids level returned to the original in 6 h of nitrate re-supply after 24 h starvation. Since protein biosynthesis and degradation depend on nitrogen availability, cyanobacteria degrade the abundant phycbiliproteins in response to the nitrogen depletion. To estimate contribution of phycobiliproteins degradation to the amino acids pool, we studied fluctuation of amino acids in a mutant that lacks nblA1/A2 genes, which are indispensable for degradation. We will also report amount of newly synthesized amino acids under nitrogen poor condition.