Researchers at The Hong Kong University of Science and Technology discovered a novel specialized organelle called the dracosphera in Chaetoderma shenloong, a deep-sea mollusk living in cold seeps in the South China Sea.
The newly identified survival structure was uncovered in Chaetoderma shenloong. The study focused on this organism, an aplacophoran mollusc living in anoxic sediments tens of centimetres below the seafloor surface, according to a study published in Nature Communications.
An international group of scientists—featuring Yunlong Li, Chong Chen, and Jin Sun alongside various peers from facilities both within China and internationally—carried out the investigation. Although cold seep ecosystems receive no sunlight, they are rich in methane and hydrogen sulfide.
Financial backing for the project came from several entities, including the Guangzhou Laboratory, the Natural Science Foundation of Shandong Province, the National Key Research and Development Program of China, the Laoshan Laboratory, and financial support provided by the HKSAR Government.
Anatomy of the Dracosphera
Within the digestive gland of C. shenloong, the research team identified a dedicated spherical compartment for housing its sulphur-oxidising bacterial symbionts. This structure is roughly 10 to 15 micrometres across, and the digestive gland of C. shenloong is hypertrophied and intricately reticulate, while the animal has otherwise lost most of its gut.
This is the first time researchers have identified a specialised organelle dedicated to chemosynthesis in an animal. Numerous animal lineages inhabiting reducing settings like cold seeps and hydrothermal vents have developed partnerships involving chemoautotrophic bacteria, wherein these microbes occasionally reside inside host cells inside distinct formations known as bacteriocytes.
Unlike simple enclosure within host cell membranes, the dracosphera introduces a novel approach to symbiotic integration by cultivating bacteria inside spherical compartments made of multiple lamellar layers.
Adapting to Hypoxic Environments
Survival becomes exceedingly difficult for both the host animal and its symbiotic partners due to the profound lack of oxygen found within these mud strata.
This newly uncovered survival strategy, dedicated to preserving bacterial partnership, sheds fresh light on the survival tactics used by deep-sea creatures in nearly oxygen-depleted habitats, thereby creating fresh avenues for investigating deep-sea ecosystems, organelle development, and chemosymbiosis.
This mutually beneficial relationship allows Chaetoderma shenloong to survive in resource-limited deep-sea environments.