Introduction to the Cyanobacteria - UCMP

Thompson AW, Foster RA, Krupke A, et al. (2012) Unicellular cyanobacterium symbiotic with a single‐celled eukaryotic alga. Science 337: 1546–1550.

T1 - A quantitative model for inorganic carbon fluxes and photosynthesis in cyanobacteria

AB - A model for inorganic carbon fluxes and photosynthesis in cyanobacteria is proposed and quantified, with special reference to Anabaena variabilis. -from Authors

Introduction to the Cyanobacteria

Zehr JP (2011) Nitrogen fixation by marine cyanobacteria. Trends in Microbiology 19: 162–173.

How did they do it? The simple cells of cyanobacteria can reproduce quickly, in onlyabout 30 minutes. When conditions change, the members of a colony that are best able tocope are the ones that tend to survive, and since the reproduction time is so short, theiroffspring can be manifold and continue the growth of the colony. In this process of"natural selection," the colony soon consists only of individual bacteriaadapted to the new conditions. It is a different type of survival than we usuallyassociate with more complex forms of life. For example, if there is a harsh winter, we areinterested in whether enough individuals of lived through the winter and can establish abreeding stock to produce a next generation that can continue the species. With cyanobacteria in stromatolite, there may be as many as 10,000 generations in a singlelong, harsh winter. Thus, the survival depends on the most cold-tolerant members of thecolony producing offspring, and the nature of the members of the colony will be subtlymodified at the end of the ordeal. If a hot summer follows, then the process of naturalselection will favor those that survived the harsh winter but still have some heattolerance.

Find out information about cyanobacteria

Chen Y‐B, Zehr JP and Mellon M (1996) Growth and nitrogen fixation of the diazotrophic filamentous nonheterocystous cyanobacterium Trichodesmium sp. IMS 101 in defined media: evidence for a circadian rhythm. Journal of Phycology 32: 916–923.

Purple and green bacteria and cyanobacteria are photosynthetic

Cyanobacteria are oxygenic photosynthetic bacteria that are widespread in marine, freshwater and terrestrial environments, and many of them are capable of fixing atmospheric nitrogen. However, ironically, nitrogenase, the enzyme that is responsible for the reduction of N2, is extremely sensitive to O2. Therefore, oxygenic photosynthesis and N2 fixation are not compatible. Hence, cyanobacteria had to evolve a variety of strategies circumventing this paradox, allowing them to grow at the expense of N2, a ubiquitous source of nitrogen. Some filamentous cyanobacteria differentiate heterocysts. These cells lack the oxygenic photosystem and possess a glycolipid cell wall that keeps the oxygen concentration sufficiently low for nitrogen fixation to take place. This strategy is known as spatial separation of oxygenic photosynthesis and nitrogen fixation. Nonheterocystous cyanobacteria may temporally separate these processes by fixing nitrogen during the night. Again others use a combination of these strategies.

Nitrogen Fixation in Cyanobacteria

Cohen Y, Jørgensen BB, Revsbech NP and Poplawski R (1986) Adaptation to hydrogen sulfide of oxygenic and anoxygenic photosynthesis among cyanobacteria. Applied and Environmental Microbiology 51: 398–407.

Cyanobacteria: Life History and Ecology

You have already studied the "dark reaction" and I will refer you to Dr. Diwan's notes on the subject. As the overall process of photosynthesis involves a series of electron transfer reactions, we are in the realm of oxidation-reduction chemistry, and it would help to review the basics of these processes because we will be going into this topic in greater depth. There is a direct analogy to electron transfer in the mitochondrion, in which clumps of energy are transferred from one electron carrier to another along a "chain" and H+ ions are translocated out, across the mitochondrial membrane, thus generating an electrochemical gradient. The energy inherent in this gradient is used to synthesize ATP in the process of "oxidative phosphorylation." The same processes occur in photosynthesis and the chloroplast, the site of photosynthesis in plants and blue-green algae (but not in photosynthetic bacteria), is the analog of the mitochondrion in eukaryotes.