Modifying the Cyanobacterial Metabolism as a Key to Efficient Biopolymer Production in Photosynthetic Microorganisms

Abstract

Cyanobacteria are photoautotrophic bacteria commonly found in the natural environment. Due to the ecological benefits associated with the assimilation of carbon dioxide from the atmosphere and utilization of light energy, they are attractive hosts in a growing number of biotechnological processes. Biopolymer production is arguably one of the most critical areas where the transition from fossil-derived chemistry to renewable chemistry is needed. Cyanobacteria can produce several polymeric compounds with high applicability such as glycogen, polyhydroxyalkanoates, or extracellular polymeric substances. These important biopolymers are synthesized using precursors derived from central carbon metabolism, including the tricarboxylic acid cycle. Due to their unique metabolic properties, i.e., light harvesting and carbon fixation, the molecular and genetic aspects of polymer biosynthesis and their relationship with central carbon metabolism are somehow different from those found in heterotrophic microorganisms. A greater understanding of the processes involved in cyanobacterial metabolism is still required to produce these molecules more efficiently. This review presents the current state of the art in the engineering of cyanobacterial metabolism for the efficient production of these biopolymers.

Accumulation of PHA in the Microalgae Scenedesmus sp. under Nutrient-Deficient Conditions

“…Related metabolic processes in bold in medium-color boxes. Critical enzymes in light- Various studies suggest that there are important interrelations between the PHA biosynthetic pathway and those of the central carbon metabolism [46], especially the glycogen pathway, one of the major cellular carbohydrate forms in cyanobacteria, which is degraded to a simpler compound: glucose. Dutt and Srivastava [47] showed that in PHA accumulating microalga photosynthetically grown under N-depletion, up to 87% of the carbon in PHB is derived from intracellular carbon reserves rather than from the CO2 fixed during the cultivation, but it was not clear which specific metabolic routes related with carbon fixation provided precursors for PHA synthesis.…”

Homologs of Circadian Clock Proteins Impact the Metabolic Switch Between Light and Dark Growth in the Cyanobacterium Synechocystis sp. PCC 6803

“…Though the physiological role of PHB is still largely unclear, recent studies suggest a function of PHB as an electron sink during unbalanced conditions and as an additional carbon storage to prevent a metabolic spillover (Koch and Forchhammer, 2021 ). This complex relationship links PHB synthesis and utilization to central metabolic pathways (Ciebiada et al, 2020 ; Koch et al, 2020b ). Therefore, the transcriptomic changes might not fully represent the effects of KaiAB1C1 and RpaA deficiency for cellular night- and daytime functions, which led us to analyze the metabolic changes in the two corresponding mutants.…”

Homologs of circadian clock proteins impact the metabolic switch between light and dark growth in the cyanobacteriumSynechocystissp. PCC 6803

“…PHB synthesis depends on many factors, such as the C:N ratio and nutrient starvation. A complex relationship links PHB synthesis and utilization to central metabolic pathways (Ciebiada et al, 2020;Koch et al, 2020). Therefore, the transcriptomic changes might not fully represent the role of KaiAB1C1 and RpaA in cellular nightand daytime functions, which led us to analyze the metabolic changes in the two corresponding mutants.…”