초록
<P>Potassium (K<SUP>+</SUP>) is an essential macronutrient for all living organisms including cyanobacteria. Cyanobacteria are a group of bacteria performing oxygenic photosynthesis, widely studied in basic and applied sciences. The primary metabolism of the unicellular cyanobacterium <I>Synechocystis</I> sp. PCC 6803 is altered by environmental conditions, and it excretes organic acids and hydrogen under dark, anaerobic conditions. Here we demonstrated that K<SUP>+</SUP> widely changes the primary carbon metabolism of this cyanobacterium. Succinate and lactate excretion from the cells incubated under dark, anaerobic conditions was enhanced in the presence of K<SUP>+</SUP>, while hydrogen production was repressed. The addition of K<SUP>+</SUP> and the genetic manipulation of acetate kinase AckA and an RNA polymerase sigma factor SigE additively increased succinate and lactate production to 141.0 and 217.6 mg/L, which are 11 and 46 times, compared to the wild-type strain without K<SUP>+</SUP>, respectively. Intracellular levels of 2-oxoglutarate, succinate, fumarate, and malate increased by K<SUP>+</SUP> under dark, anaerobic conditions. This study provides the evidence of the considerable effect of K<SUP>+</SUP> on the biosynthesis of anionic metabolites in a unicellular cyanobacterium.</P>