Recent Advances in the Photoautotrophic Metabolism of Cyanobacteria: Biotechnological Implications

Abstract

Cyanobacteria constitute the only phylum of oxygen-evolving photosynthetic prokaryotes that shaped the oxygenic atmosphere of our planet. Over time, cyanobacteria have evolved as a widely diverse group of organisms that have colonized most aquatic and soil ecosystems of our planet and constitute a large proportion of the biomass that sustains the biosphere. Cyanobacteria synthesize a vast array of biologically active metabolites that are of great interest for human health and industry, and several model cyanobacteria can be genetically manipulated. Hence, cyanobacteria are regarded as promising microbial factories for the production of chemicals from highly abundant natural resources, e.g., solar energy, CO2, minerals, and waters, eventually coupled to wastewater treatment to save costs. In this review, we summarize new important discoveries on the plasticity of the photoautotrophic metabolism of cyanobacteria, emphasizing the coordinated partitioning of carbon and nitrogen towards growth or compound storage, and the importance of these processes for biotechnological perspectives. We also emphasize the importance of redox regulation (including glutathionylation) on these processes, a subject which has often been overlooked.

Recent Advances in Developing Artificial Autotrophic Microorganism for Reinforcing CO2 Fixation

“…The CBB cycle is ubiquitous in autotrophic microorganisms, primarily occurring in cyanobacteria. Remarkable progress has been made in producing biofuel and chemicals from CO 2 and solar energy by engineering the native CBB cycle in cyanobacteria, including ethanol, butanol, lactic acid, acetone, isobutyraldehyde, isoprene, and biodiesel (Savakis and Hellingwerf, 2015;Veaudor et al, 2020). However, the titer of target products is unsatisfactory (Hagemann and Hesse, 2018;Luan et al, 2020).…”

Genetic, Genomics, and Responses to Stresses in Cyanobacteria: Biotechnological Implications

“…Furthermore, the NAD(P)H dehydrogenase transcription factor (NdhR, Sll1594), homologous to the proteobacterial regulators of the Calvin−Benson−Bassham metabolic pathway (CbbR, hereafter referred to as Calvin cycle), does not regulate the transcription of Calvin cycle genes [ 91 ]. Instead, NdhR regulates numerous genes involved in the transport and assimilation of inorganic carbon (CO 2 and bicarbonate) [ 6 , 92 , 93 ].…”

“…Synechocystis PCC 6803 in being one of the few cyanobacteria capable to grow under photoautotrophic, mixotrophic, or heterotrophic conditions [ 147 ] has become the best studied cyanobacterium. It serves as model to study the photoautotrophic metabolism [ 6 , 7 , 93 ], the crucial importance of the carbon/nitrogen metabolic balance [ 6 , 93 ], and the responses to stresses [ 35 ]. Such investigations are also carried out, to a lesser extent, with Synechococcus PCC 7002 and Synechococcus PCC 7942.…”

“…Synechocystis PCC 6803 and Synechococcus PCC 7002, which can both use exogenous carbohydrates to accelerate their growth [ 6 ], possess lexA , which encodes a transcription regulator involved in carbon assimilation, not DNA repair [ 90 ]. In contrast, the obligate photoautotroph Synechococcus PCC 7942 has no lexA [ 58 ].…”

“…Cyanobacteria are regarded as the producer of the atmospheric oxygen (O 2 ) of Earth [ 3 ] and the ancestors of the plant chloroplast [ 4 ]. Cyanobacteria capture solar energy at high efficiencies (3–9%) [ 5 ] to power up their efficient photoautotrophic metabolism, which fixes huge amounts of inorganic carbon (CO 2 , NaHCO 3 , and Na 2 CO 3 ) and nitrogen (N 2 , NH 4 , NO 2 , NO 3 , or urea) [ 6 , 7 ], into an enormous biomass [ 8 ] that supports a large part of the food chain.…”