Metagenomics Analysis Reveals An Extraordinary Bacterial Diversity in Anisakids (Nematoda: Anisakidae) L3 Larvae

Abstract Background : L3 larvae of anisakid nematodes are an important problem for the fisheries industry and pose a potential risk for human health by acting as agents causing allergies and as potential vectors of pathogens microrganisms. In spite of the close bacteria-nematode relationship very little is known of the Anisakids microbiote. Fresh fish could be contaminated by bacteria vectored in the cuticle or in the intestine of Anisakids when the L3 larvae migrate through the muscles. As a consequence the bacterial inoculum will be spread, affecting the quality of the fish, and possible clinical effects cannot be discarded Results : A total of 2,689,113 16S rRNA gene sequences from a total of 113 L3 individuals obtained from fish captured along the FAO 27 area were studied. Bacteria were taxonomically characterized through 1803 representative OTUsequences. Fourteen Phyla, 31 Classes, 52 Orders, 129 Families and 187 genera were unambiguously identified. We have found as part of microbiome an average of 123 OTUs per L3 individual. Diversity Indices (Shannon and Simpson indices) indicate an extraordinary diversity of bacteria at a OTU level. There are clusters of Anisakids individuals (samples) defined by the associated bacteria which however are not significantly related with fish hosts or anisakid taxa. This suggests that association or relationship among bacteria in Anisakids, exists without the influence of fishes or nematodes. The lack of relationships with hosts of Anisakids taxa has to be necessarily expresssed by the association among bacterial OTUs or other taxonomical levels which are ranging from OTUs to phylum level. Conclusions : There are significant biological structural associations of microbiota in anisakid nematodes which manifest in clusters of bacteria ranging from plyllum to genus level which could also be anindicator of degree of fish contamination or from the geographic zone of fish capture. Actinobacteria, Aquificae, Firmicutes, and Proteobacteria are the phyla whose abundance value discriminate for difining such structures.