Oxalate decarboxylase is involved in turnover of 2-phosphoglycolate in Synechocystis sp. strain PCC 6803

Despite the presence of a carbon concentrating mechanism, cyanobacteria synthesize 2- phosphoglycolate (2PG) by the oxygenase reaction of Rubisco. Using DNA-microarray analyses, we examined the regulation of genes involved in 2PG metabolism in the cyanobacterium Synechocystis PCC 6803. While genes for the plant-like C2 cycle were barely influenced by low Ci conditions, genes of the bacterial-like glycerate pathway were upregulated. Notably, genes encoding enzymes for a potential third route of 2PG degradation, decarboxylation via oxalate and formate, were induced as well. In order to define the relative roles of these three pathways, single-, double- and triplemutants with defects in participating enzymes were generated. Evaluation of their resistance toward oxalate indeed suggests the presence of a threefold branched metabolism of photorespiratory 2PG in Synechocystis.