Insights into the Natural Defenses of a Coral Reef Fish Against Gill Ectoparasites: Integrated Metabolome and Microbiome Approach

Abstract

Understanding natural defense mechanisms against parasites can be a valuable tool for the development of innovative therapies. We have previously identified a butterflyfish species (Chaetodon lunulatus) that avoids gill monogenean parasites while living amongst closely related parasitized species. The metabolome and microbiome of several sympatric butterflyfish species from the island of Moorea (French Polynesia) were previously described. In this study, we used the previously generated datasets in an attempt to identify metabolites and bacteria potentially involved in parasite defense mechanisms. We investigated the interplay between the gill mucus metabolome and microbiome of the non-susceptible C. lunulatus versus sympatric butterflyfish species that were always found parasitized in the Central and Eastern Indo-Pacific. After observing significant differences between the metabolome and bacteria of susceptible versus non-susceptible fish, we obtained the discriminant metabolites and operational taxonomic units (OTUs) using a supervised analysis. Some of the most important discriminant metabolites were identified as peptides, and three new peptides derived from β-subunit hemoglobin from C. lunulatus (CLHbβ-1, CLHbβ-2, and CLHbβ-3) were purified, characterized and synthesized to confirm their structures. We also identified specific bacterial families and OTUs typical from low-oxygen habitats in C. lunulatus gill mucus. By using a correlation network between the two datasets, we found a Fusobacteriaceae strain exclusively present in C. lunulatus and highly correlated to the peptides. Finally, we discuss the possible involvement of these peptides and Fusobacteriaceae in monogenean avoidance by this fish species.

Diversity and structure of sparids external microbiota (Teleostei) and its link with monogenean ectoparasites

“…The first hypothesis is a shift in fish gut microbiota that could be indirectly transferred to the skin through the aquatic environment from fish feces [ 23 ]. Alternatively, variations in diet are known to result in changes within the external mucus in terms of secretion and production of metabolites which subsequently can affect microbial diversity and composition [ 40 , 41 , 118 ]. Therefore, diet could be a stronger determinant of the whole microbial community structure in teleost fish species but the characterization of such metabolites and their correlation with diet has yet to be confirmed.…”

“…However, the mechanisms of establishment and the determinants of the specificity and attraction of monogeneans to their hosts remain poorly known [ 39 ]. Recent work suggested that external bacterial communities have a role in the production of chemical stimuli that interact with monogenean larvae [ 40 , 41 ]. Increasing evidence supports close interaction between parasitic species and fish microbiota, which in turn influences host physiology [ 42 – 44 ].…”

Metabolomics and Marine Biotechnology: Coupling Metabolite Profiling and Organism Biology for the Discovery of New Compounds

“…For example, cyclic dipeptides found in the algae Taonia atomaria were found to be highly correlated with a BD1-7 clade bacterial taxon from the Alteromanadaceae family (Paix et al, 2019). Similarly, several hemoglobin-derived peptides found in the butterflyfish Chaetodon lunulatus were highly correlated to a Fusobacteriaceae strain (Reverter et al, 2020), suggesting a possible direct or indirect involvement of these bacteria in the production of the aforementioned compounds.…”

“…Within this context, the combined study of the holobiont microbiome and metabolome provides new exciting opportunities to explore host-symbiont relationships. Identification of consistent coassociations between compounds and microorganisms using correlation tools can assist in metagenomics mining to search for natural product biosynthetic gene clusters (BGCs) in the holobionts (Paix et al, 2019;Reverter et al, 2020, Figure 2). For example, cyclic dipeptides found in the algae Taonia atomaria were found to be highly correlated with a BD1-7 clade bacterial taxon from the Alteromanadaceae family (Paix et al, 2019).…”

Molecular characterization and expression analysis of suppressors of cytokine signalling from golden pompano ( Trachinotus ovatus )

“…Using the immune strategies (e.g. vaccine development) to prevent the occurrence of fish diseases is urgent due to the drug resistance and environmental destruction that caused by the using of traditional chemical drugs in aquaculture (Reverter et al, 2020). Understanding the fish immune system is important for these strategies.…”