Abstract
Chitin is often reported in molluscan shell, where it likely contributes to the mechanical strength of the biomineral. However, the role of this polysaccharide in relation to the process of shell formation is not well understood. We investigated the deposition of chitin during shell repair in the Eastern oysters, Crassostrea virginica, by inserting stainless steel and glass implants in a region of shell damage. This work documents the time course of deposition of both chitin fibrils and calcium carbonate layers. Chitin is detected by confocal laser scanning microscopy (CLSM) using a chitin-specific fluorescent probe that was produced from clones of a chitin-binding domain. The presence of fibrils was confirmed using electron microscopy of implants. The fibrils’ dimensions were reduced after treatment with both acid and bleach, suggesting that chitin interacts with inorganic minerals and other organic components such as proteins and lipid as early as in 5 hours after shell damage. With CLSM, it was shown that chitin co-localized with membrane, suggesting the importance of cells located on the implants in the process of fibril formation. Using observations from this study as well as those from the literature on chitin synthase production in molluscs and fungi, we propose a cellular mechanism of chitin deposition related to shell formation.
Highlights
Chitin is the second most abundant naturally occurring polysaccharide after cellulose (Kumar, 2000; Cohen, 2010), and this biopolymer is a subject of major interest in material science (Merzendorfer and Zimoch, 2003)
One of the goals of biomineralization research is to use approaches that capture the involvement of cells and molecules in this process as close to their native biological state as possible
Established work on chitin in mineral and biological samples were often treated using harsh chemicals such as NaOH or bleach (Peters, 1972; Ehrlich et al, 2010, 2013). These approaches were effective in revealing the chemical-resistant chitin fibers, cells and other molecules were degraded
Summary
Chitin is the second most abundant naturally occurring polysaccharide after cellulose (Kumar, 2000; Cohen, 2010), and this biopolymer is a subject of major interest in material science (Merzendorfer and Zimoch, 2003). It has a crystalline structure made up of straight chain polysaccharides and is typically used by organisms for structural support (Stern and Jedrzejas, 2008). The ß-form is commonly hydrated and associated with proteins, such as in the cell walls of diatoms, and the internal skeleton of cephalopods (Carlström, 1957; Brunner et al, 2009). The ß-form is commonly hydrated and associated with proteins, such as in the cell walls of diatoms, and the internal skeleton of cephalopods (Carlström, 1957; Brunner et al, 2009). Kaya et al (2017) characterized γ-chitin extracted from the cocoon of a moth and the stomach of a squid and concluded that this rarer form of chitin is structurally more similar to α- than ß-chitin
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