Cyanobacteria which sequesters carbonate granules internally

Cyanobacterial metabolism is quite interesting leading to different kinds of products ranging from biofuels, sugars, isoprene, carbonates. Until now, what have been found with cyanobacteria is extracellular carbonate deposits but it is recently found that a specie of cyanobacteria produce intracellular carbonate deposits. This specie has been given the nomenclature as order Gloeobacterales, Candidatus Gloeomargarita lithophora.

During photosynthesis,CO₂ is fixed leading to a more alkaline environment inside the cell. This makes the cells excrete alkalinity outside and if calcium is present in the environment, carbonate precipitates and form crystals with it leading to calcium carbonate deposits.

But, in these cyanobacteria the mechanism for excreting carbonates is either not present because of their ancient origin or the reason could be something that makes this phenomenon advantageous for them. The probable advantage of these inclusions is that they raise the density of cells to ~12% which has been predicted to be useful for these ancient benthic organisms to stay grounded.

The intracellular granules are found to be ~270nm and average number of inclusions per cell are ~21. These inclusions are rich in Ca, Ba, Sr,Mg and their ratios in the granules indicates their abundance in the local environment.

Reference: Couradeau E, Benzerara K, Gérard E, Moreira D, Bernard S, Brown GE Jr, López-García P. An early-branching microbialite cyanobacterium forms intracellular carbonates. Science. 2012 Apr 27;336(6080):459-62.