The Multiple Functions of Common Microbial Carbon Polymers, Glycogen and PHB, during Stress Responses in the Non-Diazotrophic Cyanobacterium Synechocystis sp. PCC 6803

Abstract

Classical microbial carbon polymers such as glycogen and polyhydroxybutyrate (PHB) have a crucial impact as both a sink and a reserve under macronutrient stress conditions. Most microbial species exclusively synthesize and degrade either glycogen or PHB. A few bacteria such as the phototrophic model organism Synechocystis sp. PCC 6803 surprisingly produce both physico-chemically different polymers under conditions of high C to N ratios. For the first time, the function and interrelation of both carbon polymers in non-diazotrophic cyanobacteria are analyzed in a comparative physiological study of single- and double-knockout mutants (ΔglgC; ΔphaC; ΔglgC/ΔphaC), respectively. Most of the observed phenotypes are explicitly related to the knockout of glycogen synthesis, highlighting the metabolic, energetic, and structural impact of this process whenever cells switch from an active, photosynthetic ‘protein status’ to a dormant ‘glycogen status’. The carbon flux regulation into glycogen granules is apparently crucial for both phycobilisome degradation and thylakoid layer disassembly in the presence of light. In contrast, PHB synthesis is definitely not involved in this primary acclimation response. Moreover, the very weak interrelations between the two carbon-polymer syntheses indicate that the regulation and role of PHB synthesis in Synechocystis sp. PCC 6803 is different from glycogen synthesis.

Transcriptome Analysis of Polyhydroxybutyrate Cycle Mutants Reveals Discrete Loci Connecting Nitrogen Utilization and Carbon Storage in Sinorhizobium meliloti

“…There is not a clear mechanism for the allocation of carbon between glycogen synthesis and PHB synthesis in S. meliloti . In cyanobacteria, it has been proposed that carbon is diverted to glycogen (over PHB) during nitrogen stress ( 19 ). Unlike PHB, glycogen forms granules that are water soluble, and they are generally much smaller than PHB granules ( 20 ).…”

Effects of Reduced and Enhanced Glycogen Pools on Salt-Induced Sucrose Production in a Sucrose-Secreting Strain of Synechococcus elongatus PCC 7942

“…However, glycogen can also serve as a reserve of excess carbon under imbalanced nutrient conditions (26). Moreover, the crucial functions of glycogen for cyanobacterial acclimation to unfavorable environments such as nutrient starvation (26)(27)(28)(29) and salt and oxidative stress (30) were also reported. Glycogen synthesis is catalyzed by glucose-1-phosphate adenylyltransferase (GlgC) providing ADP-glucose, which is then used by glycogen synthase (GlgA).…”

Pontiella desulfatans gen. nov., sp. nov., and Pontiella sulfatireligans sp. nov., Two Marine Anaerobes of the Pontiellaceae fam. nov. Producing Sulfated Glycosaminoglycan-like Exopolymers

“…Strains F1 T and F21 T showed the genetic potential for producing and using glycogen ( glgABCPX , Table S1 ) and polyphosphate ( ppk, ppx ; Table S1 ), but not polyhydroxyalkanoates. Transmission electron microscopy of strain F1 T cells in exponential phase confirmed the presence of intracellular storage polymer granules ( Figure 4 ), which appear electron-light since they do not stain with the applied osmium tetroxide or uranyl acetate [ 50 , 51 , 52 ]. A polyphosphate staining was negative for cells in exponential growth, indicating glycogen was probably the only energy storage compound formed in the conditions tested.…”