Question

Describe the unique qualities of cyanobacteria with respect to energy production.

Answer 1

Most cyanobacteria are photoautotrophic organisms [some are also photoheterotrophic, which means they use light to generate ATP but they must obtain carbon inorganic form] that fix CO2 and release O2. Cyanobacteria have a special environmental adaptation for surviving in low CO2 concentrations, the CO2 concentrating mechanism(CCM). This mechanism actively transports and accumulates inorganic carbon(HCO3- and CO2) within the cell, creating a high CO2 concentration pool around the CO2‐fixing enzyme, Rubisco(Ribulose‐1,5‐ bisphosphate carboxylase oxygenase is an enzyme that helps to convert carbon dioxide into sugars). You’ll see this special CCM type mechanism show up later in plants as C4 photosynthesis.

Another unique characteristic of some cyanobacteria is their ability to fix elemental (gaseous) nitrogen. They do not have to rely on other combined nitrogen sources. The enzyme complex responsible for this nitrogen fixation is called nitrogenase. In low N2 environments, cyanobacteria will produce heterocysts, which are larger, thicker‐walled cells that are better at fixing nitrogen. They are one of the very few groups of organisms that can convert inert atmospheric nitrogen into an oxidized form, such as nitrate(NO3-) or nitrite(NO2-) a reduced form as in ammonium (NH3) (rhizobium bacteria is found in soil and on some plant, roots can do this too). Nitrification can not occur, however, in the presence of oxygen, so heterocysts are thick-walled and anaerobic. Heterocysts are present as the larger, thick‐walled cells in the filaments such as in Nostoc or Anabaena. The ability of cyanobacteria to fix elemental nitrogen has made it is a very important agricultural asset. They have been used as nitrogen fertilizers in the cultivation of rice and beans.