Genesis of amorphous calcium carbonate containing alveolar plates in the ciliate Coleps hirtus (Ciliophora, Prostomatea)

Abstract

In the protist world, the ciliate Coleps hirtus (phylum Ciliophora, class Prostomatea) synthesizes a peculiar biomineralized test made of alveolar plates, structures located within alveolar vesicles at the cell cortex. Alveolar plates are arranged by overlapping like an armor and they are thought to protect and/or stiffen the cell. Although their morphology is species-specific and of complex architecture, so far almost nothing is known about their genesis, their structure and their elemental and mineral composition. We investigated the genesis of new alveolar plates after cell division and examined cells and isolated alveolar plates by electron microscopy, energy-dispersive X-ray spectroscopy, FTIR and X-ray diffraction. Our investigations revealed an organic mesh-like structure that guides the formation of new alveolar plates like a template and the role of vesicles transporting inorganic material. We further demonstrated that the inorganic part of the alveolar plates is composed out of amorphous calcium carbonate. For stabilization of the amorphous phase, the alveolar vesicles, the organic fraction and the element phosphorus may play a role.

Proteins as Functional Units of Biocalcification – An Overview

“…(2) the formation of an array of macromolecules and its subsequent targeting to the site of mineralization; (3) the pumping of inorganic ionic precursors to set up a saturated environment; and finally (4), the control of certain proteins over crystal nucleation, growth and inhibition, providing a scaffold for mineral deposition. Although biologically controlled mineralization is present in microorganisms such as bacteria (magnetotactic [2]) and unicellular algae (diatoms [3], coccolithophores [4]) or protozoans (ciliates [5]), the process is undeniably more broadly represented in animals. Non-vertebrates in particular can produce a wide-range of external CaCO 3biominerals such as shells (in mollusks and in brachiopods), carapaces (in crustaceans), exoskeletons (in corals and sponges) and calcified tubes (in serpulid annelids), but also internal ones like spicules and spines (in sponges and echinoderms, respectively) and gastroliths (in crustaceans).…”

Inorganic phosphate in growing calcium carbonate abalone shell suggests a shared mineral ancestral precursor

“…Phosphorus is also found in the mineralizing protist world, first as inorganic phosphate anions incorporated into the calcite without disrupting the structure 27 , similarly to Mg 2+ in some calcified-biomineralized systems 28 and secondly as element of the organic mineral-associated molecules like phosphorylated proteins, metabolites (phosphoenolpyruvate) and polyphosphates, used as ACC stabilizing agent. In the ectoplasmic plates of the alveolate protist Coleps hirtus, phosphorus and calcium colocalize but are correlated with the organic part of the alveolar plates 29 . Phosphorus is also found within a pool of intracellular calcium in the coccolith-forming Emiliania huxleyi haptophyte algae 30 .…”

Negative Curvature and Control of Excitable Biological Media

“…An interesting example, which is still not well understood, is the biomineralization process of calcium carbonates, as found in many invertebrate biominerals such as alveolar plates of ciliates (single-cell eukaryotic micro-organism) [131] and mollusk shells. The latter in particular is still not understood in terms of mechano-sensory response to the extremely hard shell (∼GPa).…”