Oysters Have Genes to Help in Adapting to Stress in Harsh Environment

Scienists have sequenced the complete genome of the Pacific oyster (Crassostrea gigas), shedding light on their shell formation and stress response.

Pacific oysters are bivalve molluscs belonging to the family Ostreidae. This is the first molluscan genome sequenced in order to understand their evolution and adaptation to marine environments, according to a report from BGI-Shenzhen, a Chinese operator of genome-sequencing centers.

"The accomplishment is a major breakthrough in the international Conchological research, with great advancement in the fields of Conchology and Marine Biology," Professor Fusui Zhang, Academician of Chinese Academy of Sciences, said in the report from BGI-Shenzhen.

"The study will provide valuable resources for studying the biology and genetic improvement of molluscs and other marine species," he said.

Based on their study, researchers have found that the oysters have a total of around 28,000 genes which also includes a set of genes that helps them to manage with temperature variation, environmental stress and other changes such as water salinity and exposure to air as they adapt to intertidal zones.

Intertidal zones are the areas between tide marks where several inhabitants such as starfish, sea urchins and molluscs have to adapt to extreme harsh environments. Water quality changes from fresh rain water to high saline and dry salt water in these environments. The habitats get exposed to the sun most of the time and also to extreme cold temperatures.

Apart from the genes that help in coping with stress, experts also noticed that the oysters have immune-related genes in their digestive gland, suggesting that the digestive system played a significant role in defending pathogens.

The genome sequencing also gave insights into oyster's shell formation. An oyster's shell is made up of calcium carbonate (CaCo3) crystals, which provides protection from predators and desiccation (extreme dryness) as they are sessile mammals that do not roam about freely and are fixed to a hard surface.

While experts have suggested two models for the formation of shells in oysters, both are believed to be inaccurate. They are planning to compare the genome of Crassostrea gigas with that of other mollusc species such as California sea hare so as to understand their biology.

The findings of the study are published in the journal Nature.