The mud-dwelling clam Meretrix petechialis secretes endogenously
synthesized erythromycin
Xin Yue cs 2022 PNAS 119,e2214150119 doi org/10.1073/pnas.2214150119

... how do invertebrate spp native to microbe-rich habitats like
mud-flats survive in a pathogen-laden world, without an anticipatory,
specific & lymphocyte-based immune system?
Here, we demonstrate:
- the mud-dwelling clam Meretrix petechialis synthesizes, stores &
secretes erythromycin (EM is a potent antibiotic AB, whose production
had thus far only been reported in certain actinomycete spp),
- specific cells beneath the mantle epithelia (which interfaces with the
clam’s environment) are the synthesis & storage sites of this
macrolide, providing protection against bacterial challenge.

Lacking an adaptive immune system, and often living in habitats with
dense & diverse bacterial populations, marine invertebrates thrive in
the presence of potentially challenging microbial pathogens,
but the mechanisms underlying this resistance remain largely unexplored,
and promise to reveal novel strategies of microbial resistance.
Here, we provide evidence:
the mud-dwelling clam Meretrix petechialis synthesizes, stores &
secretes the AB erythromycin EM.
Liquid chromatography + mass spectrometry, immuno-cytochemistry,
fluorescence in situ hybridization, RNA interference & enzyme-linked
immuno-sorbent assay revealed:
this potent macrolide (thought to be synthesized only by
micro-organisms) is produced by specific mucus-rich cells beneath the
clam’s mantle epithelium, which interfaces directly with the
bacteria-rich environment.
The AB activity was confirmed by bacterio-static assay.
Genetic, onto-, phylo-genetic & genomic evidence (incl. genotypic
egregation ratios in a family of full siblings, gene expression in clam
larvae, phylogenetic tree & synteny conservation in the related genome
region) further revealed:
the genes responsible for EM production are of animal origin.
The detection of this AB in another clam species showed:
the production of this macrolide is not exclusive to M.petechialis,
it may be a common strategy among marine invertebrates.
The finding of EM production by a marine invertebrate offers a striking
example of convergent evolution in secondary metabolite synthesis
between the animal & bacterial domains.
These findings open the possibility of engineering-animal tissues for
the localized production of an anti-bacterial secondary metabolite.

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