Vibrio splendidus clade associated with a disease affecting Paracentrotus lividus (Lamarck, 1816) in Sardinia (Western Mediterranean)

Antibiotic Resistance in Vibrio Bacteria Associated with Red Spotting Disease in Sea Urchin Tripneustes gratilla (Echinodermata)

The red spotting disease harms sea urchins to the extent of mass mortality in the ocean and echinocultures, accompanied by environmental damage and economic losses. The current study emphasizes the antimicrobial resistance of three isolated bacteria, closely related to Vibrio harveyi, Vibrio owensii, and Vibrio fortis, associated with red spotting in the cultured sea urchin Tripneustes gratilla. In vitro trials examined the susceptibility of these bacterial isolates to various antibiotics. In addition, using an in silico examination, we revealed the arsenal of antimicrobial resistance genes in available genomes of various pathogenic Vibrio associated with diseases in sea urchins, fish, shellfish, and corals. These two approaches enabled the discussion of the similarities and differences between aquatic pathogenic Vibrio and their antibiotic resistance. Among them, we revealed a core resistance to tetracyclines and penams by the in vitro examined strains. At the same time, the in silico study also supported this core resistance by the presence of the adeF and CRP genes in the bacterial genomes. Nevertheless, variability and specific resistance were evident at the species and strain levels in the Vibrio bacteria and genomes. The in vitro trials highlighted the diverse resistance of the Vibrio harveyi-like isolate to all examined antibiotics, while the other two isolates were found susceptible to nitrofurantoin and sulfamethoxazole. The resistance of the Vibrio harveyi-like isolate could not have been obtained in the genome of the proposed relative of Vibrio harveyi VHJR7 that lacks the oqxA and oqxB genes, which enables such a resistance. A unique sensitivity of the Vibrio fortis-like isolate to erythromycin is proposed when compared to other isolated Vibrio and Vibrio genomes that seem capable of resisting this drug. According to the results, we propose nitrofurantoin or sulfamethoxazole for treating two of the red-spotting-associated isolates (Vibrio fortis and Vibrio owensii-like), but not Vibrio harveyi-like. We assume that a shared resistance to some antibiotics by Vibrios is gained by a horizontal gene transfer while previous exposures of a bacterial strain to a specific drug may induce the development of a unique resistance. Finally, we discuss the novel knowledge on antibiotic resistance in Vibrio from the current research in light of the potential risks when using drugs for disease control in aquaculture.

Unravelling the main immune repertoire of Paracentrotus lividus following Vibrio anguillarum bath challenge

Paracentrotus lividus is the most abundant echinoid species in the North East Atlantic Ocean and Mediterranean Sea. Although there is abundant genomic information of the species, there is no deep characterisation of the genes involved in the immune response. Here, a reference transcriptome of male and female coelomocytes was produced. The generated P. lividus transcriptome assembly has 203,511 transcripts, N50 transcript length of 1079 bp, and more than 90% estimated gene completeness in Eukaryota and Metazoa BUSCO databases, respectively. Differential gene expression analyses showed 54 and 55 up-regulated genes in P. lividus female and male coelomocyte tissues, respectively. These results suggest a similar immune gene repertoire between sexes. To examine the immune response, P. lividus was challenged with Vibrio anguillarum, one of the candidate pathogens for bald disease. Immune parameters were evaluated at cell and humoral levels, as well as the expression analysis of immune related genes at an early response stage. No differences were found at cellular and humoral levels with the exception of the increase of nitric oxide in perivisceral fluid of challenged animals. At the gene expression level, a total of 2721 genes were upregulated in challenged animals, 13.6 times higher expression than control group. Our analysis revealed that four major KEGG pathways were enriched in challenged animals: Autophagy (KEGG:04140), Endocytosis (KEGG:04144), Phagosome (KEGG:04145) and Protein processing in endoplasmic reticulum (KEGG:04141). Several toll-like receptors (TLR), scavenger receptors cysteine-rich (SRCR) or nucleotide-binding oligomerisation domain like receptors (NLR) were identified as major family genes for pathogen recognition and immune defence. This study provides a valuable transcriptomic resource and unfolds the molecular basis of immune response to V. anguillarum exposure. Overall, our findings contribute to the conservation effort of the P. lividus populations, as well as its sustainable exploitation in an aquaculture context.

Spotting disease disrupts the microbiome of infected purple sea urchins, Strongylocentrotus purpuratus

BACKGROUND

Spotting disease infects a variety of sea urchin species across many different marine locations. The disease is characterized by discrete lesions on the body surface composed of discolored necrotic tissue that cause the loss of all surface appendages within the lesioned area. A similar, but separate disease of sea urchins called bald sea urchin disease (BSUD) has overlapping symptoms with spotting disease, resulting in confusions in distinguishing the two diseases. Previous studies have focus on identifying the underlying causative agent of spotting disease, which has resulted in the identification of a wide array of pathogenic bacteria that vary based on location and sea urchin species. Our aim was to investigate the spotting disease infection by characterizing the microbiomes of the animal surface and various tissues.

RESULTS

We collected samples of the global body surface, the lesion surface, lesioned and non-lesioned body wall, and coelomic fluid, in addition to samples from healthy sea urchins. 16S rRNA gene was amplified and sequenced from the genomic DNA. Results show that the lesions are composed mainly of Cyclobacteriaceae, Cryomorphaceae, and a few other taxa, and that the microbial composition of lesions is the same for all infected sea urchins. Spotting disease also alters the microbial composition of the non-lesioned body wall and coelomic fluid of infected sea urchins. In our closed aquarium systems, sea urchins contracted spotting disease and BSUD separately and therefore direct comparisons could be made between the microbiomes from diseased and healthy sea urchins.

CONCLUSION

Results show that spotting disease and BSUD are separate diseases with distinct symptoms and distinct microbial compositions.

A scuticociliate causes mass mortality of Diadema antillarum in the Caribbean Sea

Echinoderm mass mortality events shape marine ecosystems by altering the dynamics among major benthic groups. The sea urchin Diadema antillarum, virtually extirpated in the Caribbean in the early 1980s by an unknown cause, recently experienced another mass mortality beginning in January 2022. We investigated the cause of this mass mortality event through combined molecular biological and veterinary pathologic approaches comparing grossly normal and abnormal animals collected from 23 sites, representing locations that were either affected or unaffected at the time of sampling. Here, we report that a scuticociliate most similar to Philaster apodigitiformis was consistently associated with abnormal urchins at affected sites but was absent from unaffected sites. Experimentally challenging naïve urchins with a Philaster culture isolated from an abnormal, field-collected specimen resulted in gross signs consistent with those of the mortality event. The same ciliate was recovered from treated specimens postmortem, thus fulfilling Koch's postulates for this microorganism. We term this condition D. antillarum scuticociliatosis.

The “Bald Disease” of the Sea Urchin Paracentrotus lividus: Pathogenicity, Molecular Identification of the Causative Agent and Therapeutic Approach

In recent decades, various species of Mediterranean sea urchins, including Paracentrotus lividus, have been subject to widespread seasonal episodes of mass mortality whose causative agents are still unclear. In particular, P. lividus is subject to late winter events of mortality, due to a disease manifested by a massive loss of spines and the presence of greenish amorphous material on the tests (i.e., the sea urchin skeleton consisting of spongeous calcite). Documented mortality events show a seasonal epidemic diffusion and might produce economic losses also in aquaculture facilities, besides the environmental constraints to its diffusion. We collected individuals showing conspicuous lesions on the body surface and reared them in recirculated aquaria. Samples of external mucous were collected along with coelomic liquids and cultured to isolate bacterial and fungal strains, further submitted to molecular identification through the amplification of prokaryotic 16S rDNA. In addition, pools of infected sea urchins were reared in recirculated tanks after short baths in a formulated therapeutic compound and their survival rates were compared to non-treated individuals for variable periods. Here, we aimed at a redescription of the etiopathogenetic nature of the parasites and tested the efficacy of a possible treatment, to be proposed for aquaculture purposes.

Bald sea urchin disease shifts the surface microbiome on purple sea urchins in an aquarium

Bald sea urchin disease (BSUD) is most likely a bacterial infection that occurs in a wide range of sea urchin species and causes the loss of surface appendages. The disease has a variety of additional symptoms, which may be the result of the many bacteria that are associated with BSUD. Previous studies have investigated causative agents of BSUD, however, there are few reports on the surface microbiome associated with the infection. Here, we report changes to the surface microbiome on purple sea urchins in a closed marine aquarium that contracted and then recovered from BSUD in addition to the microbiome of healthy sea urchins in a separate aquarium. 16S rRNA gene sequencing shows that microhabitats of different aquaria are characterized by different microbial compositions, and that diseased, recovered, and healthy sea urchins have distinct microbial compositions, which indicates that there is a correlation between microbial shifts and recovery from disease.

Detection of microplastics and phthalic acid esters in sea urchins from Sardinia (Western Mediterranean Sea)

The occurrence of microplastics (MPs) and phthalic acid esters (PAEs) in wild purple sea urchins (Paracentrotus lividus) of Sardinia (Italy, Western Mediterranean Sea) was surveyed. Specifically, MPs were analyzed in the digestive tract by μFTIR and PAEs in the gonads by SPME-LC-MS/MS. 9 out of 22 specimens resulted contaminated with MPs and 20 displayed levels of PAEs over the quantification limit. A total of 23 MPs were detected with a maximum concentration of 4 microplastics/individual in the commercially undersized specimens. PAEs displayed average concentration of 32 ng/g, σ = 5.3 with maximum value of 77 ng/g. The most abundant congeners were DEHP (17 ng/g, σ = 4.3) and DBP (10 ng/g, σ = 2.5). Statistical analysis showed correlation between DEHP and fiber concentrations and among the concentration of MEP, DEP, DBP and BBzP. Due to local use of sea urchin gonads as gourmet delicacy, the potential human exposition to MPs and PAEs by consumption is also discussed.