Amorphous Calcium Carbonate Granules Form Within an Intracellular Compartment in Calcifying Cyanobacteria
2018
The recent discovery of
cyanobacteriaforming
intracellular
amorphous calcium carbonate(ACC) has challenged the former paradigm suggesting that
cyanobacteria-mediated carbonatogenesis was exclusively extracellular. Yet, the mechanisms of
intracellular
biomineralizationin
cyanobacteriaand in particular whether this takes place within an
intracellularmicrocompartment, remain poorly understood. Here, we analyzed six cyanobacterial strains forming
intracellularACC by transmission electron microscopy. We tested two different approaches to preserve as well as possible the
intracellularACC inclusions: (i) freeze-substitution followed by epoxy embedding and room-temperature
ultramicrotomyand (ii) high-pressure freezing followed by cryo-
ultramicrotomy, usually referred to as
cryo-electron microscopyof vitreous sections (CEMOVIS). We observed that the first method preserved ACC well in 500-nm-thick sections but not in 70-nm-thick sections. However, cell ultrastructures were difficult to clearly observe in the 500-nm-thick sections. In contrast, CEMOVIS provided a high preservation quality of bacterial ultrastructures, including the
intracellularACC inclusions in 50-nm-thick sections. ACC inclusions displayed different textures, suggesting varying brittleness, possibly resulting from different hydration levels. Moreover, an electron dense envelope of ~2.5 nm was systematically observed around ACC granules in all studied cyanobacterial strains. This envelope may be composed of a protein shell or a lipid monolayer, but not a lipid bilayer as usually observed in other bacteria forming
intracellularminerals. Overall, this study evidenced that ACC inclusions formed and were stabilized within a previously unidentified
bacterial microcompartmentin some species of
cyanobacteria.
Keywords:
-
Correction
-
Source
-
Cite
-
Save
59
References
21
Citations
NaN
KQI