Friday, October 18, 2013

DNA Fingerprinting of Pearls

Pearls produced by oysters of the Pteriidae family are among the most valuable and oldest gems. Oyster shells and pearls have been used for human adornment since antiquity. Today pearls are cultured in domesticated saltwater oysters and freshwater mussels and have become a billion dollar industry. Whereas a natural pearl forms without any human intervention in a wild oyster, a cultured pearl is the result of a human-induced injury. The value assigned to a pearl depends largely on its quality, rarity, and whether it originated naturally or through culture. Thus there is significant interest in being able to scientifically document the provenance of both historic natural pearls and modern cultured pearls. This is rarely possible for the most valuable white to slightly cream-colored pearls using current methods such as UV-visible photospectrometry and micro-Raman spectroscopy. The higher value of natural pearls has led to many fraudulent attempts to pass off cultured pearls as natural ones. To date, the distinction between natural and cultured pearls has been based on X-ray shadow images and more recently X-ray computer microtomography.

Now a group of Swiss researchers successfully developed a DNA-based method to determine the oyster species that produced a pearl as a first step towards providing more precise information regarding its likely geographical origin. Their DNA fingerprinting technique can be used to differentiate pearls from different oysters that were deliberately or accidentally mixed and may eventually differentiate cultured pearls that have been mixed in with natural pearls.

Although largely build from calcium carbonate pearls contain up to 4% organic matter which seems to contain enough well preserved DNA even when pearls were harvested years earlier. The research group was able to recover sequences from different loci (ITS, 16S, COI) longer than 650bp. For better success the team had also developed a micro-drilling technique to extract the DNA. This drilling does not affect the commercial value of an investigated pearl.

h/t Claudia Steinke

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