Abstract
The organic matrix (OM) contained in marine calcifiers has a key role in the regulation of crystal deposition, such as crystalline structure, initiation of mineralization, inhibition, and biological/environmental control. However, the functional properties of the chitin-rich skeletal organic matrix on the biological aspect of crystallization in crustose coralline algae have not yet been investigated. Hence, the characterization of organic matrices in the biomineralization process of this species was studied to understand the functions of these key components for structural formation and mineralization of calcium carbonate crystals. We purified skeletal organic matrix proteins from this species and explored how these components are involved in the mineralization of calcium carbonate crystals and environmental control. Intriguingly, the analytical investigation of the skeletal OM revealed the presence of chitin in the crustose coralline alga Leptophytum foecundum. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis of the OM revealed a high molecular mass protein as 300-kDa. Analysis of glycosylation activity exposed two strong glycoproteins as 300-kDa and 240-kDa. Our study of the biominerals of live collected specimens found that in addition to Mg-calcite up to 30% aragonite were present in the skeleton. Our experiment demonstrated that the chitin-rich skeletal OM of coralline algae plays a key role in the biocalcification process by enabling the formation of Mg-calcite. In addition, this OM did not inhibit the formation of aragonite suggesting there is an as yet unidentified process in the living coralline that prevents the formation of aragonite in the living skeletal cell walls.
Highlights
While abundant data is available on the organic matrices of corals, calcareous sponges, and molluscans[1,2,3,4,5,6,7], very little is known about coralline algal organic matrices and their role in calcification
We previously found chitin in the organic matrix of skeletons from a different type of coralline alga, Clathromorphum compactum, and the chitin appears to contribute to the biomineralization process[21]
We investigated the role of skeletal organic matrix in biomineralization of the coralline alga L. foecundum
Summary
While abundant data is available on the organic matrices of corals, calcareous sponges, and molluscans[1,2,3,4,5,6,7], very little is known about coralline algal organic matrices and their role in calcification. The organic matrix components contained in calcifying marine organisms play a key role in controlling the formation of calcium carbonate (CaCO3) minerals in the biomineralization process, in response to changes of seawater chemistry[1,2,7,10,11]. The skeletal formation of biominerals is controlled by two interacting mechanisms: (1) the secretion of OM proteins and (2) the transportation of ions (e.g., magnesium, calcium, bicarbonates, and protons) to the site of mineralization (in the case of calcification)[2,33] Organic matrix macromolecules, such as proteins and polysaccharides, play an important role in the process of biologically controlled calcification[2,34]. Specimens used in this study were live collected at 16–18 m water depth at Port Manvers Bay, Labrador, Canada (56°57.10 N, 61°32.80 W) in 2013
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