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

Abstract

L3 larvae of anisakid nematodes are an important problem for the fisheries industry and pose a potential risk for human health by acting as infectious agents causing allergies and as potential vectors of pathogens and microrganisms. In spite of the close bacteria–nematode relationship very little is known of the anisakids microbiota. 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, with potential effects on the quality of the fish, and possible clinical effects cannot be discarded. 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 fishing area were studied. Bacteria were taxonomically characterized through 1803 representative operational taxonomic units (OTUs) sequences. 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) indicate an extraordinary diversity of bacteria at an OTU level. There are clusters of anisakids individuals (samples) defined by the associated bacteria which, however, are not significantly related to 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 expressed by the association among bacterial OTUs or other taxonomical levels which range from OTUs to the phylum level. There are significant biological structural associations of microbiota in anisakid nematodes which manifest in clusters of bacteria ranging from phylum to genus level, which could also be an indicator of fish contamination or the geographic zone of fish capture. Actinobacteria, Aquificae, Firmicutes, and Proteobacteria are the phyla whose abundance value discriminate for defining such structures.

Tardigrade Community Microbiomes in North American Orchards Include Putative Endosymbionts and Plant Pathogens

“…Combined, the tardigrades in these studies represent a diverse set of species, including wild and laboratory-reared specimens isolated from multiple continents, suggesting that the predominance of these phyla is broadly characteristic of the microbiome of Tardigrada, regardless of species or location. These phyla, especially Proteobacteria , are also dominant in the microbiomes of other Ecdysozoans, including soil nematodes ( Adam et al, 2014 ; Dirksen et al, 2016 ; Elhady et al, 2017 ), marine nematodes ( Arcos et al, 2021 ), and insects ( Colman et al, 2012 ; Engel and Moran, 2013 ). The tardigrade microbiota therefore appears similar to that of other Ecdysozoans at the phylum level.…”

“…Another tardigrade-associated genus, Micrococcus , was differentially abundant across both locations and years ( Supplementary Table S9 ). This genus has been reported from the cuticles of soil nematodes ( Adam et al, 2014 ) as well as fish parasitic nematodes ( Arcos et al, 2021 ), suggesting that Micrococcus may be associated with the tardigrade cuticle. Another notable tardigrade-associated genus in this study was Nakamurella , represented primarily by OTU 33, which showed differential abundance across locations ( Supplementary Table S9 ).…”

Tardigrade community microbiomes in North American orchards include putative endosymbionts and plant pathogens

“…Combined, the tardigrades in these studies represent a diverse set of species, including wild and laboratory-reared specimens isolated from multiple continents, suggesting that the predominance of these phyla is broadly characteristic of the microbiome of Tardigrada, regardless of species or location. These phyla, especially Proteobacteria, are also dominant in the microbiomes of other Ecdysozoans, including soil nematodes (Dirksen et al 2016;Elhady et al 2017;Adam et al 2014), marine nematodes (Arcos et al 2021), and insects (Colman, Toolson, and Takacs-Vesbach 2012;Engel and Moran 2013). The tardigrade microbiota therefore appears similar to that of other Ecdysozoans at the phylum level.…”

“…Another tardigradeassociated genus, Micrococcus, was differentially abundant across both locations and years (Table S9). This genus has been reported from the cuticles of soil nematodes (Adam et al 2014) as well as fish parasitic nematodes (Arcos et al 2021), suggesting that Micrococcus may be associated with the tardigrade cuticle. Another notable tardigrade-associated genus in this study was Nakamurella, represented primarily by OTU 33, which showed differential abundance across locations (Table S9).…”

Editorial for the Special Issue “Parasitic Diseases from Wild Animals with Emphasis on Zoonotic Infections”

“…Finally, there is a need for a holistic approach to understanding diseases provoked by pathogens, including environmental factors, co-infections and co-morbidities, and interanimal and human-animal interactions that produce changes in the prevalence and severity of the diseases. In this context, an unusual paper relating the microbiota that a zoonotic parasite, such as Anisakis, can inoculate to humans is included in this Special Issue [11].…”