Mechanism concentrates inorganic carbon : Diatomaceae

Magnified 6500X, this scanning electron micrograph (SEM) of an untreated water specimen extracted from a wild stream mainly used to control flooding during inclement weather, revealed the presence of unidentified organisms, which included bacteria, protozoa, and algae. In this particular image, a single unidentified diatomic microorganism was depicted revealing its wondrous symmetrical ultrastructural morphology.

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"Diatoms growing in their natural aquatic habitats operate inorganic C concentrating mechanisms (CCMs), which provide a steady-state CO2 concentration around Rubisco higher than that in the medium. How these CCMs work is still a matter of debate. However, it is known that both CO2 and HCO3– are taken up, and an obvious but as yet unproven possibility is that active transport of these species across the plasmalemma and/or the four-membrane plastid envelope is the basis of the CCM. In one marine diatom there is evidence of C4-like biochemistry which could act as, or be part of, a CCM. Alternative mechanisms which have not been eliminated include the production of CO2 from HCO3– at low pH maintained by a H+ pump, in a compartment close to that containing Rubisco." (Roberts et al. 2007:79)