Microbiota and gut ultrastructure of Anisakis pegreffii isolated from stranded cetaceans in the Adriatic Sea

Abstract

Background Inferring the microbiota diversity of helminths enables depiction of evolutionarily established ecological and pathological traits that characterize a particular parasite-host interaction. In turn, these traits could provide valuable information for the development of parasitosis control and mitigation strategy. The parasite Anisakis pegreffii (Nematoda: Anisakidae) realizes the final stage of its life-cycle within gastric chambers of aquatic mammals, causing mild-to-moderate granulomatous gastritis with eosinophilic infiltrate, to severe ulcerative gastritis with mixed inflammatory infiltrate, often associated with bacterial colonies. However, its interaction with the host microbiota remains unknown, and might reveal important aspects of parasite colonization and propagation within the final host. Methods MySeq Illumina sequencing was performed for the 16S rRNA gene from microbiota isolated from larvae, and uterus and gut of adult A. pegreffii parasitizing stranded striped dolphins ( Stenella coeruleoalba ). To assess the potential presence of Brucella ceti within isolated microbiota, Brucella -targeted real-time PCR was undertaken. In addition, TEM of the gastrointestinal tract of the infective third-stage (L3) and transitioning fourth-stage larvae (L4) was performed to characterize the morphological differences and the level of larval feeding activity. Results In total, 230 distinct operational taxonomic units (OTUs) were identified across all samples ( n = 20). The number of shared taxa was lower than the number of taxa found specifically in each parasite stage or organ. The dominant taxon was Mycoplasmataceae (genus Mycoplasma ) in the gut and uterus of adult A. pegreffii , whereas Fusobacteriaceae (genus Cetobacterium ) was the most abundant in 40% of larvae, alongside Mycoplasmataceae . No B. ceti DNA was detected in any of the microbiota isolates. TEM revealed differences in gut ultrastructure between L3 and L4, reflecting a feeble, most likely passive, level of feeding activity in L3. Conclusions Microbiota from L3 was more related to that of the gut rather than the uterus of adult A. pegreffii . Taxa of the larval microbiota showed qualitative and quantitative perturbations, likely reflecting the propagation through different environments during its life-cycle. This suggests an ontogenetic shift in the alpha and beta diversity of microbial communities from uterus-derived towards cetacean-derived microbiota. Although TEM did not reveal active L3 feeding, microbiota of the latter showed similar...

A Visitor of Tropical Waters: First Record of a Clymene Dolphin (Stenella clymene) Off the Patagonian Coast of Argentina, With Comments on Diet and Metazoan Parasites

“…Interestingly, all anisakid nematodes collected in this study were classified as L4 larvae of A. pegreffii. We suggest that the Clymene dolphin may acts as a definitive host for this species, because A. pegreffii mature in the stomach of other dolphin species (e.g., Mladineo et al, 2019;Pons-Bordas et al, 2020). We believe that these nematodes were likely recruited by the Clymene dolphin in Patagonia.…”

Host-Parasite Interaction between Parasitic Cymothoid Ceratothoa oestroides and Its Host, Farmed European Sea Bass (Dicentrarchus labrax)

“…Considering that C. oestroides lives in buccal cavity of its host with a sufficient oxygen supply where it can rely on oxidative metabolism, lipid storage over glycogen storage is more feasible, compared to some endoparasites, e.g. nematodes, in which glycogen storage is favored due to hypoxic environment of host's body cavities in which they reside [32]. The presence of numerous vesicles around lipid droplets with likely proteinaceous content remains puzzling.…”

Functional Ultrastructure of the Excretory Gland Cell in Zoonotic Anisakids (Anisakidae, Nematoda)

“…Although Anisakis sp. L3 are non-active feeding stages, a recent study demonstrated the presence of several vesicles in the L3 intestinal lumen, potentially originating from passive intake during migration through the tissues of their paratenic hosts [41]. It is likely that a part of these “ingesta” in the form of nutrients finally reaches the EC and passes by endocytosis, as the cell is already active at this larval stage and requires energy for ES production.…”

“…Alternatively, anaerobic glycolysis that mostly occurs in the cytosol in an oxygen-independent metabolic pathway converts glucose into pyruvate, storing the energy in form of ATP and NADH. Both somatic muscle and enterocytes of L3 have been observed rich in glycogen [41], suggesting that glycolysis might be an important metabolic pathway at the larval stage, engaged also in functioning of the EC.…”