Journal Article

Plant-Like C2 Glycolate Cycle and the Bacterial-Like Glycerate Pathway Cooperate in Phosphoglycolate Metabolism in Cyanobacteria

Eisenhut, Marion, Kahlon, Shira, Ruth, Wolfgang, Kaplan, Aaron, Hasse, Dirk, Bauwe, Hermann, Ogawa, Teruo, Ewald, Ralph, Lieman-Hurwitz, Judy, Hagemann, Martin

2006

Overview

The occurrence of a photorespiratory 2-phosphoglycolate metabolism in cyanobacteria is not clear. In the genome of the cyanobacterium Synechocystis sp. strain PCC 6803, we have identified open reading frames encoding enzymes homologous to those forming the plant-like C2 cycle and the bacterial-type glycerate pathway. To study the route and importance of 2-phosphoglycolate metabolism, the identified genes were systematically inactivated by mutagenesis. With a few exceptions, most of these genes could be inactivated without leading to a high-CO₂-requiring phenotype. Biochemical characterization of recombinant proteins verified that Synechocystis harbors an active serine hydroxymethyltransferase, and, contrary to higher plants, expresses a glycolate dehydrogenase instead of an oxidase to convert glycolate to glyoxylate. The mutation of this enzymatic step, located prior to the branching of phosphoglycolate metabolism into the plant-like C2 cycle and the bacterial-like glycerate pathway, resulted in glycolate accumulation and a growth depression already at high CO₂. Similar growth inhibitions were found for a single mutant in the plant-type C2 cycle and more pronounced for a double mutant affected in both the C2 cycle and the glycerate pathway after cultivation at low CO₂. These results suggested that cyanobacteria metabolize phosphoglycolate by the cooperative action of the C2 cycle and the glycerate pathway. When exposed to low CO₂, glycine decarboxylase knockout mutants accumulated far more glycine and lysine than wild-type cells or mutants with inactivated glycerate pathway. This finding and the growth data imply a dominant, although not exclusive, role of the C2 route in cyanobacterial phosphoglycolate metabolism.

• Publisher: American Society of Plant Biologists,American Society of Plant Physiologists
• Subject: (S)-2-hydroxy-acid oxidase / Alcohol Oxidoreductases / Alcohol Oxidoreductases - metabolism / Bacteria / Bacterial Proteins / Bacterial Proteins - physiology / Bioenergetics and Photosynthesis / Biological and medical sciences / Carbon Dioxide / Carbon Dioxide - metabolism / Cell growth / Cyanobacteria / Cyanophyta / DNA Mutational Analysis / Enzymes / Fundamental and applied biological sciences. Psychology / Gene Expression Regulation, Bacterial / genes / Genes, Bacterial / genetics / Genomes / Glyceric Acids / Glyceric Acids - metabolism / Glycine / Glycine - metabolism / Glycine Decarboxylase Complex / Glycine Decarboxylase Complex - genetics / Glycine Hydroxymethyltransferase / Glycine Hydroxymethyltransferase - metabolism / Glycolates / Glycolates - metabolism / Glyoxylates / growth & development / knockout mutants / Lysine / Lysine - metabolism / Metabolism / Mutation / Open Reading Frames / phenotype / Photosynthesis, respiration. Anabolism, catabolism / physiology / Plant physiology and development / Plants / Protein metabolism / recombinant proteins / rev genes / Serine / Serine - metabolism / Synechocystis / Synechocystis - genetics / Synechocystis - growth & development / Synechocystis - metabolism