Glycine accumulation is toxic for the cyanobacterium Synechocystis sp. strain PCC 6803, but can be compensated by supplementation with magnesium ions.

The observation that accumulation of the amino acid glycine is associated with strong growth inhibition or even death in cyanobacteria, plants and humans led to the hypothesis that glycine might act toxically if a certain threshold is exceeded. In this report, it is shown that Synechocystis PCC 6803 wild-type cells could sustain higher glycine addition than mutants impaired in enzymes using glycine such as the T-protein of the glycine decarboxylase complex or PurT involved in purine biosynthesis. A mutant defective in the glycine uptake system was barely influenced by external glycine. This shows that the intracellular level of accumulated glycine is critical. The toxic effect could be alleviated by addition of MgCl(2), suggesting that glycine might be toxic by reducing intracellular Mg(2+) ions, which are essential for many vital processes.