Clam Becomes First Known Animal to Make Its Own Antibiotic

Optical microscope of the SSU Laboratory of Optics and BiophotonicsMary ManleyErythromycin is a type of antibiotic used to treat a number of bacterial infections, and until now, the antibiotic was thought to be only made by actinobacteria. Researchers are now revealing an unlikely animal which synthesizes its own erythromycin. The Asiatic hard clam (Meretrix petechialis) has been found by researchers to make its own erythromycin. The clam is able to synthesize the complex antibiotic through particular mucus-rich cells in their protective, outer mantle tissue. The clam, which lives in mud flat environments, can synthesize, store, and secrete the antibiotic into the bacteria-rich habitat where it lives.Prior to the study, scientists were unaware of how clams resisted bacterial pathogens in their bacterial-dense populations when they lack adaptive, lymphocyte-based immune systems. Researchers began by searching for genes in the clam that changed their expression before and after infections. They then identified a gene encoding an enzyme as part of the formation of an intermediate compound in the biosynthesis of erythromycin.”The discovery made us wonder if erythromycin is synthesized in the clam,” explains Xin Yue, a marine biologist at the Chinese Academy of Sciences in Qingdao, who adds that animals may be genetically engineered to make their own antibiotics, following the discovery of the Asiatic hard clam.”However, our results suggested that the erythromycin-producing genes in M. petechialis have an origin in animal lineages and represent convergent evolution with bacteria,” said Professor Liu Baozhong, an author of the study who led a research team from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS).”We also documented erythromycin production in a related species, Meretrix lyrate, which suggests that the antibiotic may be more widely produced by marine invertebrates,” said Yue, first author of the study published in the journal PNAS last week.Margaret McFall-Ngai, who is an expert in microbial interactions with marine mollusks at the University of Hawaii, notes that invertebrates don’t have a sophisticated immune system but will often “maintain very simple interactions with the microbial world—either they associate with a few species, or they just say no”.While the discovery is exciting for the Asiatic hard clam, it is also a groundbreaking insight into the environmental and immune defense abilities of invertebrates as a group, as well as a first look at the potential for resistance breeding.

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