Cyanobacteria

Features

Photosynthetic

• Phycocyanin gives bluish color ("blue-green algae")

• Chlorophyll a, which has peak absorption in the red and violet spectra

• The chloroplasts in plants, which contain chlorophyll a, comes from endosymbiosis with a cyanobacterium 

Nitrogen-fixation

• Many "fix" nitrogen, converting gaseous N2 into ammonia (NH3), nitrate (NO3), or nitrite (NO2)

• These bacteria use a structure called the heterocyst to convert the atmospheric nitrogen to a solid (usable) form

• These bacteria have been known to form root relationships with cycads and Azolla and a single angiosperm (Gunnera), as well as non-root-forming organisms, like hornworts, some green algae (e.g. Chlorella), and lichens that form symbioses with cyanobacteria

• ** The nitrogen-fixing associations in nodule-forming plants occur with rhizobial bacteria in the legumes (Fabaceae), and with actinomycete bacteria in the alders (Alnus). 

  • Rhizobial and actinomycete bacteria serve a similar nitrogen-fixation function, but are unrelated to cyanobacteria

• The conversion of nitrogen, from the gaseous phase to solid phase, is difficult because of the bonds formed by N2 

  • Cyanobacteria are the only organisms able to naturally make this conversion

  • Some nitrogen gas is converted to solid forms through lightning strikes, but this is limited

  • In the early 20th Century, an artificial form of nitrogen fixation was created, called the Haber-Bosch process

Red / pink pigmentation

• Some forms are red or pink from the pigment phycoerythrin 

• These bacteria are often found growing on greenhouse glass, or around sinks and drains. 

• The Red Sea gets its name from occasional blooms of a reddish species of cyanobacteria called Trichodesmium erythraeum

  • Trichodesmium is thought to fix nitrogen on such a scale that it accounts for almost half of the nitrogen fixation in marine systems globally (Bergman et al. 2013)

• African flamingos get their pink color from eating Spirulina, which contains a natural pink dye called canthaxanthin

Geologic Age

• Paleoarchean (3.43 billion years ago) - present

• Cyanobacteria as a whole branched off from other bacteria around 3.4 billion years ago (Fournier et al. 2021)

• This group may be as old as 3.8 bya (Eoarchean)

Stromatolites

• Stromatolites are large bacterial communities that cement sand as they grow, building up layers gradually over time.

  • The cyanobacterial layer coats the top portion of the stromatolite, conducting photosynthesis

• Possible evidence of stromatolites from Greenland sediments as early as 3.7 Ga (Nutman et al. 2016)

• Maximum diversity of stromatolites during Mesoproterozoic (between 1.0 and 1.6 billion years ago)

• Stromatolites begin to precipitously decline at about 1.0 Ga  (Bernard et al. 2013)

• Living stromatolites still survive on the western coast of Australia