Effect of amino acids on larval metamorphosis of the polychaete Hydroides elegans

Abstract

The inductive compounds that are cues for for the settlement and metamorphosis of polychaete Hydroides elegans larvae, isolated from adult homogenate of the same species and leachate of the bryozoan Bugula neritina, are known to be a mixture of amino acids. Here we investigated the toxicity of 20 amino acids on competent larvae. Nine amino acids were found to be toxic at certain concentrations. Subsequently, 12 out of 20 amino acids were assayed for their effect on larval metamorphosis of H. elegans. The effects of amino acids were decoupled from possible inductive effects of the bacteria in the bioassay system. The results showed that the amino acid isoleucine had no inductive effect on larval metamorphosis. Two acidic and 9 aliphatic amino acids directly induced larval metamorphosis. The effects of these amino acids were concentration-dependent. Among them, asparagine was the most active amino acid, and induced a high percentage of larval settlement at 1.0 × 10 -5 M, but became toxic at concentrations higher than 1.0 × 10 -4 M. The exact mechanisms by which amino acids directly induce larval metamorphosis are still unclear, although we assume that they act by binding to specific receptors and triggering the signal transduction pathway entirely or partially. KEY WORDS: Hydroides elegans · Larval metamorphosis · Chemical cue · Amino acid · BacteriaResale or republication not permitted without written consent of the publisher

Amino acid exposure modulates the bioactivity of biofilms for larval settlement of Hydroides elegans by altering bacterial community components

“…Therefore, as long as there are bacteria in testing vessels, addition of chemical extracts or compounds into the vessels will selectively change the bacterial community structures in the testing vessels as shown by Jin & Qian (2004) and by this study.…”

“…Previous work (Jin & Qian 2004) suggested that Asp, Glu, Ala, Asn, Leu, Thr and Val could induce larval settlement of Hydroides elegans directly and Ile could not. In the present study, these amino acids showed different effects on bacterial communities of biofilms and the competent larvae of H. elegans responded variously to the modified biofilms.…”

“…Adult Hydroides elegans were collected from PVC panels placed 3 m below the water surface at Long Harbor, Hong Kong (22°24' N, 114°21' E). Larvae were obtained from adults and reared to be competent according to the methods described by Jin & Qian (2004). Larval competence to settlement was tested by exposing the larvae to a welldeveloped natural marine biofilm.…”

“…Beckmann et al (1999) found that amino acid mixtures could promote biofilm development in testing dishes, which in turn triggered larval settlement, suggesting a triangular mode-of-action among cues, competent larvae and biofilms. Further study showed that amino acids induce larval settlement of H. elegans both directly and indirectly; certain amino acids promote biofilm development while others do not change bacterial abundance on the biofilm during larval settlement bioassay (Jin & Qian 2004). However, it is unknown how different amino acids affect bacterial community structures and how changes of bacterial community structures in biofilm affect a biofilm's bioactivity in larval settlement induction.…”

Exposure of biofilms to meiofaunal copepods affects the larval settlement of Hydroides elegans (Polychaeta)

“…Larvae of Hydroides elegans have been observed to prefer older biofilms, which commonly have higher bacterial densities (Jin & Qian 2004). The present study confirms those findings.…”