SUMMARYDiazotrophic cyanobacteria represent a unique group of prokaryotes that are capable of performing two physiologically conflicting processes: oxygen-generating photosynthesis and oxygen-sensitive nitrogen fixation. Adaptive evolution over millions of years has culminated in two complex, divergent strategies—spatial and temporal separation—that allow extant cyanobacteria to reconcile these antagonistic pathways. While the long-studied spatial separation strategy utilized by most filamentous strains is well understood at the molecular level, the temporal separation mechanisms in unicellular and non-heterocystous filamentous cyanobacteria remain an expanding but under-reviewed area of research. This review focuses on the orchestration of photosynthesis and nitrogen fixation in cyanobacteria, with an emphasis on temporal separation. We discuss molecular mechanisms driving the synchronization of carbon and nitrogen fixation in filamentous cyanobacteria, highlighting recent findings that elucidate the complex regulatory networks involved in maintaining an optimal C/N balance. In contrast, for unicellular cyanobacteria, where regulatory mechanisms are less defined, we synthesize various discoveries that challenge the prevailing view that these prokaryotes are metabolically disadvantaged by strict diurnal constraints. We review studies that indicate the metabolic plasticity of these strains, potentially conferred by effective oxygen-protective mechanisms, including a robust circadian clock that regulates intracellular oxygen levels. This plasticity allows adaptation to diverse diurnal conditions, preferentially segregating the incompatible processes into opposite phases while also accommodating both processes under light when daylength conditions are suboptimal. Such metabolic flexibility likely predisposes these prokaryotes to be naturally selected for nitrogen-fixing symbioses with eukaryotes and eventually, as recently demonstrated, to evolve into a nitrogen-fixing organelle.

Cyanobacteria (blue-green algae) advisories have been lifted across Alberta, according to Alberta Health Services.Recent weather has cooled lake and r...

Transition metals, including iron, zinc, copper, manganese, cobalt, nickel, and molybdenum, are vital micronutrients for microorganisms because they act as essential cofactors and structural component...

Transition metals, including iron, zinc, copper, manganese, cobalt, nickel, and molybdenum, are vital micronutrients for microorganisms because they act as essential cofactors and structural components of enzymes involved in diverse cellular processes (1, 2). Among these metals, iron is most significant because of its redox flexibility between the ferrous (Fe²+) and ferric (Fe³+) forms, which allows it to participate in essential processes such as electron transfer, cellular respiration, nitrogen fixation, DNA metabolism, and antioxidant defense (3–5). Given its central role in important cellular processes, iron is required by almost all organisms, with only a few notable exceptions such as Lactobacillus spp (6) and Borrelia burgdorferi (7). Although iron is plentiful in the Earth’s crust, its bioavailability is far below the cellular requirements because soluble ferrous iron is rapidly oxidized to insoluble ferric hydroxides at physiological pH and oxygenated conditions. In addition, pathogenic microorganisms face further iron limitation in the host, where iron is tightly sequestered by the host immune proteins like transferrin and lactoferrin, thereby restricting microbial access to this important micronutrient (4, 8).

SUMMARYDiazotrophic cyanobacteria represent a unique group of prokaryotes that are capable of performing two physiologically conflicting processes: oxygen-generating photosynthesis and oxygen-sensitive nitrogen fixation. Adaptive evolution over millions of years has culminated in two complex, divergent strategies—spatial and temporal separation—that allow extant cyanobacteria to reconcile these antagonistic pathways. While the long-studied spatial separation strategy utilized by most filamentous strains is well understood at the molecular level, the temporal separation mechanisms in unicellular and non-heterocystous filamentous cyanobacteria remain an expanding but under-reviewed area of research. This review focuses on the orchestration of photosynthesis and nitrogen fixation in cyanobacteria, with an emphasis on temporal separation. We discuss molecular mechanisms driving the synchronization of carbon and nitrogen fixation in filamentous cyanobacteria, highlighting recent findings that elucidate the complex regulatory networks involved in maintaining an optimal C/N balance. In contrast, for unicellular cyanobacteria, where regulatory mechanisms are less defined, we synthesize various discoveries that challenge the prevailing view that these prokaryotes are metabolically disadvantaged by strict diurnal constraints. We review studies that indicate the metabolic plasticity of these strains, potentially conferred by effective oxygen-protective mechanisms, including a robust circadian clock that regulates intracellular oxygen levels. This plasticity allows adaptation to diverse diurnal conditions, preferentially segregating the incompatible processes into opposite phases while also accommodating both processes under light when daylength conditions are suboptimal. Such metabolic flexibility likely predisposes these prokaryotes to be naturally selected for nitrogen-fixing symbioses with eukaryotes and eventually, as recently demonstrated, to evolve into a nitrogen-fixing organelle.

Author summary Many bacteria use microscopic, hair-like filaments called Type IV pili to crawl across surfaces or take up DNA from their surroundings. In our study, we investigated how cyanobacteria, ...