Dynamic metabolic profiling of cyanobacterial glycogen biosynthesis under conditions of nitrate depletion

Abstract

Cyanobacteria represent a globally important biomass because they are responsible for a substantial proportion of primary production in the hydrosphere. Arthrospira platensis is a fast-growing halophilic cyanobacterium capable of accumulating glycogen and has the potential to serve as a feedstock in the fermentative production of third-generation biofuels. Accordingly, enhancing cyanobacterial glycogen production is a promising biofuel production strategy. However, the regulatory mechanism of glycogen metabolism in cyanobacteria is poorly understood. The aim of the present study was to determine the metabolic flux of glycogen biosynthesis using a dynamic metabolomic approach. Time-course profiling of widely targeted cyanobacterial metabolic intermediates demonstrated a global metabolic reprogramming that involves transient increases in the levels of some amino acids during the glycogen production phase induced by nitrate depletion. Also, in vivo labelling with NaH13CO3 enabled direct measurement of metabolic intermediate turnover in A. platensis, revealing that under conditions of nitrate depletion glycogen is biosynthesized with carbon derived from amino acids released from proteins via gluconeogenesis. This dynamic metabolic profiling approach provided conclusive evidence of temporal alterations in the metabolic profile in cyanobacterial cells.

13C flux analysis of cyanobacterial metabolism

“…A similar transient 13 C labeling study was recently combined with intracellular metabolite profiling to investigate the response to nitrate depletion in cyanobacteria (Hasunuma et al 2013). In Arthrospira platensis and Synechocystis 6803, the rate of 13 C incorporation in central carbon metabolites and amino acids was determined over a thirty-minute period of labeling with NaH 13 CO 3 .…”

Identification of Four Polyhydroxyalkanoate Structural Genes in Synechocystis cf. salina PCC6909: In silico Evidences

“…Recently, the activity of the co-expressed PhaE and PhaC in a cell-free system was determined and the values obtained were comparable to those of PHA synthases belonging to class I [22]. The PhaE-C complex activity is essential for PHA polymerization but not crucial for the PHA yield, suggesting the involvement of significant regulative mechanisms combined to photosynthetic activity and glycogen biosynthesis [22][23][24]. Several attempts of genetic modification were performed mainly through the transfer of genes belonging to heterotrophic bacteria [25].…”

Photoautotrophic Polyhydroxybutyrate Granule Formation Is Regulated by Cyanobacterial Phasin PhaP in Synechocystis sp. Strain PCC 6803

“…This metabolite can be utilized for either gluconeogenesis or glycolysis, providing the necessary carbon skeletons for biosynthesis of amino acids and other metabolites required for cell growth (2), when growth conditions are suitable and nutrients are abundant. In fact, carbon flux is greatly affected by the availability of macronutrients like nitrogen (3)(4)(5) and phosphorus, which may limit growth (6). Under nutrient-limiting conditions, cyanobacteria undergo a stress adaptation process termed chlorosis (7).…”

“…This process leads to the degradation of light-harvesting complexes, causing reduced photosynthetic activity and thereby reduced metabolic activity (8). Furthermore, carbon flux is redirected toward glycogen synthesis upon macronutrient starvation (5). In addition, some cyanobacterial strains like Synechocystis sp.…”