As an autotroph, T. crunogena uses inorganic carbon (carbon dioxide and bicarbonate)
as its carbon source for synthesizing all the carbon-containing components of its biomass.
T. crunogena’s rapid growth in the presence of low concentrations of inorganic carbon
is likely due to what is known as a Carbon Concentrating Mechanism (CCM).

Thus far, CCM’s have only been well-studied in cyanobacteria.
When grown in the presence of low concentrations of inorganic carbon,
cyanobacteria express high affinity bicarbonate transporters to trap this substrate
inside their cells. Intracellular inclusions (carboxysomes) contain most
of the cell’s RubisCO (the carbon-fixing enzyme from the Calvin cycle)
and a trace of carbonic anhydrase. Carbon dioxide is provided to RubisCO
by the dehydration of bicarbonate by carbonic anhydrase.
Juxtaposition of these two enzyme activities prevents the loss of inorganic carbon
from the cells via diffusion of carbon dioxide.

Just like cyanobacteria, T. crunogena cells develop a higher affinity
for inorganic carbon when grown in the presence of low concentrations
of this substrate, likely due to both enzyme and transporter expression.
Further, carboxysomes are present in T. crunogena, as in many
chemoautotrophs.

How broadly genes for bicarbonate transporters and other adaptations
to low concentrations of inorganic carbon are distributed among chemoautotrophs
is unknown, and undermines our ability to predict the activities of these microorganisms
in the many habitats where they are found.