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

   https://doi.org/10.1093/femspd/ftad025  

   Shaw, Chloe G.; Pavloudi, Christina; Barela Hudgell, Megan A.; Crow, Ryley S.; Saw, Jimmy H.; Pyron, R. Alexander; Smith, L. Courtney (September 2023, Pathogens and Disease)

   Abstract 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. 

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2. Sea urchin microbiomes vary with habitat and resource availability

   https://doi.org/10.1002/lol2.10189  

   Miller, Paige M.; Lamy, Thomas; Page, Henry M.; Miller, Robert J. (April 2021, Limnology and Oceanography Letters)

   Abstract Sea urchins are key grazers in coastal seas, where they can survive a variety of conditions and diets, enhancing their ecological impact on kelp forests and other ecosystems. Using 16S rRNA gene sequencing, we characterized bacterial communities associated with guts of the two dominant sea urchin species in southern California, the red urchinMesocentrotus franciscanus, and the purple urchinStrongylocentrotus purpuratus. Our results show that the two urchin species have distinct gut microbiomes that vary with habitat. The taxonomic composition of their microbiomes suggests that they may facilitate digestion of food and be a source of nutrition themselves. These results highlight the role of microbiomes within macroorganisms as an extended ecological trait, and suggest that microbes may be crucial to resource use and partitioning in co‐occurring species. 

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3. Shifts in the gut microbiota of sea urchin Diadema antillarum associated with the 2022 disease outbreak

   https://doi.org/10.3389/fmicb.2024.1409729  

   Ruiz-Barrionuevo, Juliana M; Kardas, Elif; Rodríguez-Barreras, Ruber; Quiñones-Otero, Marcos A; Ruiz-Diaz, Claudia P; Toledo-Hernández, Carlos; Godoy-Vitorino, Filipa (July 2024, Frontiers in Microbiology)

   IntroductionIn recent decades, Caribbean coral reefs have lost many vital marine species due to diseases. The well-documented mass mortality event of the long-spined black sea urchinDiadema antillarumin the early 1980s stands out among these collapses. This die-off killed over 90% ofD. antillarumchanging the reefscape from coral to algal-dominated. Nearly 40 years later,D. antillarumpopulations have yet to recover. In early 2022, a new mortality event ofD. antillarumwas reported along the Caribbean, including Puerto Rico. MethodsThis study identifies the gut microbiota changes associated with theD. antillarumduring this mortality event. It contrasts them with the bacterial composition of gut samples from healthy individuals collected in 2019 by using 16S rRNA sequencing analyses. ResultsNotably, the die-off group’s core microbiome resembled bacteria commonly found in the human skin and gut, suggesting potential anthropogenic contamination and wastewater pollution as contributing factors to the 2022 dysbiosis. The animals collected in 2022, especially those with signs of disease, lacked keystone taxa normally found inDiademaincludingPhotobacteriumandPropionigenium. DiscussionThe association between human microbes and disease stages in the long-spined urchinD. antillarum, especially in relation to anthropogenic contamination, highlights a complex interplay between environmental stressors and marine health. While these microbes might not be the direct cause of death in this species of sea urchins, their presence and proliferation can indicate underlying issues, such as immune depletion due to pollution, habitat destruction, or climate change, that ultimately compromise the health of these marine organisms. 

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4. Local Genomic Instability of the SpTransformer Gene Family in the Purple Sea Urchin Inferred from BAC Insert Deletions

   https://doi.org/10.3390/genes15020222  

   Barela_Hudgell, Megan A; Momtaz, Farhana; Jafri, Abiha; Alekseyev, Max A; Smith, L Courtney (February 2024, Genes)

   The SpTransformer (SpTrf) gene family in the purple sea urchin, Strongylocentrotus purpuratus, encodes immune response proteins. The genes are clustered, surrounded by short tandem repeats, and some are present in genomic segmental duplications. The genes share regions of sequence and include repeats in the coding exon. This complex structure is consistent with putative local genomic instability. Instability of the SpTrf gene cluster was tested by 10 days of growth of Escherichia coli harboring bacterial artificial chromosome (BAC) clones of sea urchin genomic DNA with inserts containing SpTrf genes. After the growth period, the BAC DNA inserts were analyzed for size and SpTrf gene content. Clones with multiple SpTrf genes showed a variety of deletions, including loss of one, most, or all genes from the cluster. Alternatively, a BAC insert with a single SpTrf gene was stable. BAC insert instability is consistent with variations in the gene family composition among sea urchins, the types of SpTrf genes in the family, and a reduction in the gene copy number in single coelomocytes. Based on the sequence variability among SpTrf genes within and among sea urchins, local genomic instability of the family may be important for driving sequence diversity in this gene family that would be of benefit to sea urchins in their arms race with marine microbes. 

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5. Microbiome reduction and endosymbiont gain from a switch in sea urchin life history

   https://doi.org/10.1073/pnas.2022023118  

   Carrier, Tyler J.; Leigh, Brittany A.; Deaker, Dione J.; Devens, Hannah R.; Wray, Gregory A.; Bordenstein, Seth R.; Byrne, Maria; Reitzel, Adam M. (April 2021, Proceedings of the National Academy of Sciences)

   Animal gastrointestinal tracts harbor a microbiome that is integral to host function, yet species from diverse phyla have evolved a reduced digestive system or lost it completely. Whether such changes are associated with alterations in the diversity and/or abundance of the microbiome remains an untested hypothesis in evolutionary symbiosis. Here, using the life history transition from planktotrophy (feeding) to lecithotrophy (nonfeeding) in the sea urchinHeliocidaris, we demonstrate that the lack of a functional gut corresponds with a reduction in microbial community diversity and abundance as well as the association with a diet-specific microbiome. We also determine that the lecithotroph vertically transmits a Rickettsiales that may complement host nutrition through amino acid biosynthesis and influence host reproduction. Our results indicate that the evolutionary loss of a functional gut correlates with a reduction in the microbiome and the association with an endosymbiont. Symbiotic transitions can therefore accompany life history transitions in the evolution of developmental strategies. 

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