d‑Peptidase Activity in a Marine Mollusk Detoxifies a Nonribosomal Cyclic Lipopeptide: An Ecological Model to Study Antibiotic Resistance

In
the marine environment, sessile cyanobacteria have developed
chemical strategies for protection against grazers. In turn, herbivores
have to circumvent these defenses and in certain cases even take advantage
of them as shelter from their own predators. This is the case of Stylocheilus striatus, a sea hare that feeds on Anabaena torulosa, a cyanobacterium that produces
toxic cyclic lipopeptides of the laxaphycin B family. S. striatus consumes the cyanobacterium without being
affected by the toxicity of its compounds and also uses it as an invisibility
cloak against predators. In this article, using different substrates
analogous to laxaphycin B, we demonstrate the presence of an enzyme
in the digestive gland of the mollusk that is able to biotransform
laxaphycin B derivatives. The enzyme belongs to the poorly known family
of d-peptidases that are suspected to be involved in antibiotic
resistance.