Metabolite profiling of Baltic blue mussel (Mytilus sp.) hybrids and their associated microbes

Abstract

The blue mussel genus Mytilus is a popular food source and an important model organism for many scientific disciplines [1,2]. The morphologically similar species M. edulis (Me) and M. trossulus (Mt) form an unprecedented and unique hybridisation pattern in the Baltic Sea [3, 4]. Recently, it was shown that metabolite profiling of Mytilus species provides significant potential for biomonitoring of aquatic environments but also for informing natural product research [1,2]. However, the metabolome of Mytilus sp. is still little investigated and no metabolome data from the Baltic Sea blue mussels are available so far. In order to compare the metabolite profiles of Baltic Mytilus sp. at an individual level, 30 Mytilus specimens were sampled at a blue mussel farm in Kiel (Baltic Sea) and genotyped with two commonly utilized nuclear markers, EFbis and Glu-5' [4]. Genotypic assessment revealed a dominance of Mt alleles at Kiel Fjord with 90% of the samples being intermediate (Me/Mt) or Mt-like hybrids. Secondary metabolites of the whole tissue extracts (EtOAc) were explored by HPLC-DAD-MS. Metabolite profiles were found to be similar but not identical, differing mainly in minor nonpolar secondary metabolites. Considering that secondary metabolites are often produced by associated microbes and not by the macroorganism itself, the microbiome of the mussel specimens was also investigated. A culture-based approach yielded 259 bacterial and fungal strains, including Actinomycetes. Bacteria belonging to the orders Alteromonadales and Pseudomonadales (Acinetobacter sp., Pseudomonas sp., Pseudoalteromonas sp., Psychrobacter sp., Shewanella sp.) dominated the microbial community (57%). In addition, an RFLP based culture-independent approach was developed for Mytilus sp. individuals. Both the culture-dependent and culture-independent approaches showed inter-individual differences with respect to the associated microbes, but no genotypic dependence.