GABA synthesis mediated by γ-aminobutanal dehydrogenase in Synechocystis sp. PCC6803 with disrupted glutamate and α-ketoglutarate decarboxylase genes

Abstract

A pathway for polyamine-derived GABA synthesis in Synechocystis sp. PCC 6803 was explored by disrupting both the glutamate decarboxylase and α-ketoglutarate decarboxylase genes. The generated Δgad:Δkgd strain had increased intracellular α-ketoglutarate and polyamine levels compared to the wild type. Gene transcript analysis using RT-PCR indicated that the Δgad:Δkgd strain had up-regulated expression of a putative gadbh whose gene product, γ-aminobutanal dehydrogenase, would catalyze the conversion of γ-aminobutanal to GABA. A strain with disrupted gabdh showed an increase in GABA, glutamate, succinate and spermidine levels. These findings provide evidence for a link between spermidine degradation and GABA synthesis in cyanobacteria. This study highlights the role of γ-aminobutanal dehydrogenase in maintaining an intact tricarboxylic acid cycle in Synechocystis.