The mud-dwelling clam Meretrix petechialis secretes endogenously synthesized erythromycin
Contributed by Margaret McFall-Ngai; received August 17, 2022; accepted October 21, 2022; reviewed by Scott F. Gilbert and Dennis Hedgecock
Significance
An oft-asked question is how invertebrates, notably species native to microbe-rich habitats like mudflats, survive in a pathogen-laden world without an anticipatory, specific, and lymphocyte-based immune system. Here, we demonstrate that the mud-dwelling clam Meretrix petechialis synthesizes, stores, and secretes erythromycin, a potent antibiotic, whose production had thus far only been reported in certain actinomycete species. We discovered that specific cells beneath the mantle epithelia, which interfaces with the clam’s environment, are the synthesis and storage sites of this macrolide, providing protection against bacterial challenge.
Abstract
Although lacking an adaptive immune system and often living in habitats with dense and diverse bacterial populations, marine invertebrates thrive in the presence of potentially challenging microbial pathogens. However, the mechanisms underlying this resistance remain largely unexplored and promise to reveal novel strategies of microbial resistance. Here, we provide evidence that a mud-dwelling clam, Meretrix petechialis, synthesizes, stores, and secretes the antibiotic erythromycin. Liquid chromatography coupled with mass spectrometry, immunocytochemistry, fluorescence in situ hybridization, RNA interference, and enzyme-linked immunosorbent assay revealed that this potent macrolide antimicrobial, thought to be synthesized only by microorganisms, is produced by specific mucus-rich cells beneath the clam’s mantle epithelium, which interfaces directly with the bacteria-rich environment. The antibacterial activity was confirmed by bacteriostatic assay. Genetic, ontogenetic, phylogenetic and genomic evidence, including genotypic segregation ratios in a family of full siblings, gene expression in clam larvae, phylogenetic tree, and synteny conservation in the related genome region further revealed that the genes responsible for erythromycin production are of animal origin. The detection of this antibiotic in another clam species showed that the production of this macrolide is not exclusive to M. petechialis and may be a common strategy among marine invertebrates. The finding of erythromycin production by a marine invertebrate offers a striking example of convergent evolution in secondary metabolite synthesis between the animal and bacterial domains. These findings open the possibility of engineering-animal tissues for the localized production of an antibacterial secondary metabolite.
Data, Materials, and Software Availability
Both amplicon data and transcriptiomic data have been deposited in SRA database (NCBI), https://www.ncbi.nlm.nih.gov/sra (BioProject ID: PRJNA750890, BioProject ID: PRJNA747140). The gene sequence data are deposited in Genbank, https://www.ncbi.nlm.nih.gov/genbank (Accession No. MZ666239).
Acknowledgments
We thank George Somero (Stanford University) for editing the manuscript, Sladjana Prisic (University of Hawaii) for helpful comments on the manuscript, Edward Ruby (Carnegie Institution for Science) for advice on the bacteriostatic assay and manuscript editing, and Li Sun (IOCAS) for feedback on the manuscript. We also thank Yuanyuan Sun (IOCAS) for TEM sample preparation, Jianbo Yuan (IOCAS) for advice on flanking genes analysis, and Xiaoting Huang (Ocean University of China) for advice on genetic approach to analyze the origin of MpES. This work is supported by National Key R & D Program of China (2019YFD0900700), the earmarked fund for CARS-49, Youth Foundation Project (YQ2018NO07) from Qingdao National Laboratory for Marine Science and Technology (China), Shandong Province Natural Science Foundation (China) (ZR2020MD089), and National Natural Science Foundation of China (NSFC 31772845).
Author contributions
X.Y., M.M.-N., and B.L. designed research; X.Y., S.Z., H.W., J.Y., and Q.P. performed research; X.Y. analyzed data; and X.Y., M.M.-N., and B.L. wrote the paper.
Competing interests
The authors declare no competing interest.
Supporting Information
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Copyright © 2022 the Author(s). Published by PNAS. This article is distributed under Creative Commons Attribution-NonCommercial-NoDerivatives License 4.0 (CC BY-NC-ND)..
Data, Materials, and Software Availability
Both amplicon data and transcriptiomic data have been deposited in SRA database (NCBI), https://www.ncbi.nlm.nih.gov/sra (BioProject ID: PRJNA750890, BioProject ID: PRJNA747140). The gene sequence data are deposited in Genbank, https://www.ncbi.nlm.nih.gov/genbank (Accession No. MZ666239).
Submission history
Received: August 17, 2022
Accepted: October 21, 2022
Published online: November 28, 2022
Published in issue: December 6, 2022
Keywords
Acknowledgments
We thank George Somero (Stanford University) for editing the manuscript, Sladjana Prisic (University of Hawaii) for helpful comments on the manuscript, Edward Ruby (Carnegie Institution for Science) for advice on the bacteriostatic assay and manuscript editing, and Li Sun (IOCAS) for feedback on the manuscript. We also thank Yuanyuan Sun (IOCAS) for TEM sample preparation, Jianbo Yuan (IOCAS) for advice on flanking genes analysis, and Xiaoting Huang (Ocean University of China) for advice on genetic approach to analyze the origin of MpES. This work is supported by National Key R & D Program of China (2019YFD0900700), the earmarked fund for CARS-49, Youth Foundation Project (YQ2018NO07) from Qingdao National Laboratory for Marine Science and Technology (China), Shandong Province Natural Science Foundation (China) (ZR2020MD089), and National Natural Science Foundation of China (NSFC 31772845).
Author contributions
X.Y., M.M.-N., and B.L. designed research; X.Y., S.Z., H.W., J.Y., and Q.P. performed research; X.Y. analyzed data; and X.Y., M.M.-N., and B.L. wrote the paper.
Competing interests
The authors declare no competing interest.
Notes
Reviewers: S.F.G., Swarthmore College; and D.H., University of Southern California.
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The mud-dwelling clam Meretrix petechialis secretes endogenously synthesized erythromycin, Proc. Natl. Acad. Sci. U.S.A.
119 (49) e2214150119,
https://doi.org/10.1073/pnas.2214150119
(2022).
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