A Non-functional γ-Aminobutyric Acid Shunt Pathway in Cyanobacterium Synechocystis sp. PCC 6803 Enhances δ-Aminolevulinic Acid Accumulation under Modified Nutrient Conditions

Abstract

To redirect carbon flux from the γ-aminobutyric acid (GABA) shunt to the δ-aminolevulinic acid (ALA) biosynthetic pathway, we disrupted the GABA shunt route of the model cyanobacterium Synechocystis sp. PCC 6803 by inactivating Gdc, the gene-encoding glutamate decarboxylase. The generated ΔGdc strain exhibited lower intracellular GABA and higher ALA levels than the wild-type (WT) one. The ΔGdc strain’s ALA levels were ~2.8 times higher than those of the WT one when grown with levulinic acid (LA), a competitive inhibitor of porphobilinogen synthase. Abiotic stress conditions including salinity induced by 10 mM NaCl and cold at 4 °C increased the ALA levels in ΔGdc up to ~2.5 and 5 ng g−1 cell DW, respectively. The highest ALA production in the ΔGdc cyanobacteria grown in BG11 medium was triggered by glucose induction, followed by glutamate supplementation with 60 mM of LA, thereby resulting in ~360 ng g−1 cell DW of ALA, that is >300-fold higher ALA accumulation than that observed in ΔGdc cyanobacteria grown in normal medium. Increased levels of the gdhA (involved in the interconversion of α-ketoglutarate to glutamate) and the hemA (a major regulatory target of the ALA biosynthetic pathway) transcripts occurred in ΔGdc cyanobacteria grown under modified growth conditions. Our study provides critical insight into the facilitation of ALA production in cyanobacteria.

Glycine differentially improved the growth and biochemical composition of Synechocystis sp. PAK13 and Chlorella variabilis DT025

“…The microalgae can uptake the glycine using a transport system that enables direct transportation into the cell, where it can serve as a nitrogen source for the cell ( Yu et al, 2021 ). Here the difference in the rate of glycine uptake between prokaryotic Synechocystis and eukaryotic Chlorella cells may contribute to their different responses to glycine ( Gao et al, 2009 ; Kanwal and De-Eknamkul, 2023 ). In this regard, some microalgae species have been shown to preferentially utilize glycine over other nitrogen sources such as ammonium and nitrate ( Flynn and Butler, 1986 ; Tyler et al, 2005 ).…”

“…The weight of the wet biomass was then measured. Furthermore, the duplication time, the number of generations, and the specific growth rate of our sample were measured by the established protocols by Fabregas et al (1986) and utilizing the methodologies described by Jin et al (2011) and Krzemińska et al (2014). These metrics are crucial in understanding the growth characteristics of microalgae samples and were calculated to ensure the accuracy and reproducibility of the results.…”