The plant-like C2 glycolate cycle and the bacterial-like glycerate pathway cooperate in phosphoglycolate metabolism in cyanobacteria.
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-CO(2)-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 CO(2). 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 CO(2). These results suggested that cyanobacteria metabolize phosphoglycolate by the cooperative action of the C2 cycle and the glycerate pathway. When exposed to low CO(2), 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.
Eisenhut
Marion
M
Universität Rostock, Institut Biowissenschaften, Pflanzenphysiologie, D-18051 Rostock, Germany.
Kahlon
Shira
S
Hasse
Dirk
D
Ewald
Ralph
R
Lieman-Hurwitz
Judy
J
Ogawa
Teruo
T
Ruth
Wolfgang
W
Bauwe
Hermann
H
Kaplan
Aaron
A
Hagemann
Martin
M
D000429:Alcohol Oxidoreductases / Q000378:metabolism; D001426:Bacterial Proteins / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism; D004252:DNA Mutational Analysis; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D005988:Glyceric Acids / Q000378:metabolism; D005998:Glycine / Q000378:metabolism; D050959:Glycine Decarboxylase Complex / Q000235:genetics; D012696:Glycine Hydroxymethyltransferase / Q000378:metabolism; D006016:Glycolates / Q000378:metabolism*; D008239:Lysine / Q000378:metabolism; D009154:Mutation; D016366:Open Reading Frames; D012694:Serine / Q000378:metabolism; D046939:Synechocystis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
D001426:Bacterial Proteins; D005988:Glyceric Acids; D006016:Glycolates; D002245:Carbon Dioxide; D012694:Serine; D000429:Alcohol Oxidoreductases; C020819:glycolic acid dehydrogenase; D050959:Glycine Decarboxylase Complex; D012696:Glycine Hydroxymethyltransferase; C013193:phosphoglycolate; D008239:Lysine; D005998:Glycine