The role of GAD pathway for regulation of GABA accumulation and C/N balance in Synechocystis sp. PCC6803
Synechocystis sp. PCC6803 was engineered by interrupting the α-ketoglutarate decarboxylase (KGD) and overexpressing the glutamate decarboxylase (GAD) pathways to create ∆Kgd, GADox, and GADox/∆Kgd mutants with the aim to enhance GABA accumulation. Supplementation of 20 mM glutamate or 0.5 mM spermidine increased the GABA contents by several folds in engineered strains. Supplementation of glutamate not only increased the GABA accumulation of cells but also improved the growth rates of engineered strains, signifying that the GAD pathway plays a crucial role in maintaining the intracellular glutamate homeostasis in Synechocystis. The high GABA level was detected in GADox/∆Kgd grown in 0.1% glucose-supplemented medium, ~ 240-folds higher than that in WT grown without glucose. Overall results suggested that the optimization of carbon and nitrogen sources was effective in enhancing the GABA accumulation in Synechocystis overexpressing the GAD and lacking the functional KGD pathway. This work provides an insight into the strategy to improve GABA production in cyanobacteria and possibly in plants as well.
KeywordsCyanobacteria GABA production Glutamate decarboxylase Glutamate homeostasis Synechocystis sp. PCC6803
The authors are grateful to Professor Peter Lindblad, Uppsala University, Sweden, for providing the pEERM vector.
S.K. would like to thank the Graduate School of Chulalongkorn University for providing post-doctoral fellowship (Rachadaphiseksomphot Endowment Fund). A.I. acknowledges the research grant from Thailand Research Fund (IRG 5780008).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflicts of interest.
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