Open AccessDisruption of cyanobacterial γ-aminobutyric acid shunt pathway reduces metabolites levels in tricarboxylic acid cycle, but enhances pyruvate and poly(3-hydroxybutyrate) accumulation
Author(s) -
Tanakarn Monshupanee,
Chayanee Chairattanawat,
Aran Incharoensakdi
Publication year - 2019
Publication title -
scientific reports
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.24
H-Index - 213
ISSN - 2045-2322
DOI - 10.1038/s41598-019-44729-8
Subject(s) - citric acid cycle , tricarboxylic acid , chemistry , aminobutyric acid , biochemistry , pyruvate decarboxylation , metabolism , pyruvic acid , cyanobacteria , biology , bacteria , receptor , genetics
The photoautotrophic cyanobacterium Synechocystis sp. PCC 6803 assimilates carbon dioxide as the sole carbon source, and a major portion of the assimilated carbon is metabolically consumed by the tricarboxylic acid (TCA) cycle. Effects of partial interference of TCA cycle metabolic activity on other carbon metabolism have yet to be examined. Here, the γ-aminobutyric acid (GABA) shunt, one of the metabolic pathways for completing TCA cycle in Synechocystis , was disrupted via inactivating the glutamate decarboxylase gene ( gdc ). Under normal photoautotrophic condition, cell growth and the level of the TCA cycle metabolites succinate, malate and citrate were decreased by 25%, 35%, 19% and 28%, respectively, in Δ gdc mutant relative to those in the wild type (WT). The cellular levels of glycogen and total lipids of the Δ gdc mutant were comparable to those of the WT, but the intracellular levels of pyruvate and bioplastic poly(3-hydroxybutyrate) (PHB) were 1.23- and 2.50-fold higher, respectively, in Δ gdc mutant. Thus, disruption of the GABA shunt pathway reduced the TCA cycle metabolites levels, but positively enhanced the bioaccumulation of pyruvate and PHB. The PHB production rate in Δ gdc mutant was 2.0-fold higher than in the WT under normal photoautotrophy.