Biology subjects

Hewson, I.

Publications and source records attributed to Hewson, I..

9 recordsLinked to original sources

bioRxiv2026

Host-independent persistence of the Diadema antillarum Scuticociliatosis Philaster clade in coastal environments

The mass mortality of the keystone herbivore Diadema antillarum in the Caribbean was caused by the pathogenic ciliate from the Diadema antillarum Scuticociliatosis Philaster clade (DaScPc). Despite its confirmed pathogenicity, the environmental distribution and persistence strategies of DaScPc outside its host remain poorly understood. We used quantitative PCR, nested PCR, and Sanger sequencing across a 16-month time series and broad geographic surveys to investigate its ecological dynamics and potential environmental reservoirs. Sequencing-confirmed detections at a Florida coastal site devoid of D. antillarum show that DaScPc is a natural, host-independent component of the reef environment. Molecular detection on coral and macroalgal surfaces and in the plankton fraction indicates that multiple substrates can harbor the ciliate. Temporal observations revealed emerging trends with macroalgal cover and reef productivity, though no direct correlations were observed. Geographically, DaScPc was absent from outbreak sites in Panama and Reunion. Together, this data suggests spatial patchiness and a cryptic "boom-and-bust" lifestyle in which the organism persists at low abundance between outbreaks. The co-occurrence of a related nonpathogenic ciliate (Acropora/CHN/2009) further underscores the ecological complexity of the Philaster clade. These findings broaden understanding of DaScPc ecology, confirming environmental persistence independent of its host and suggesting that parasitism may be intermittent, triggered by changing environmental conditions. This work highlights the need for higher-resolution surveillance and long-term monitoring to link ecosystem processes with the reemergence of marine disease in vulnerable coral reef systems. ImportanceThe 2022 mass mortality of the sea urchin Diadema antillarum devastated Caribbean coral reefs, yet little is known about how the pathogenic ciliate responsible for the event persists in nature. We show that the Diadema antillarum Scuticociliatosis Philaster clade (DaScPc) occurs in reef environments even where the host (D. antillarum) is absent, indicating that it can persist independently of its host. Our findings suggest that DaScPc occupies a cryptic ecological niche within reef microbial communities and may follow a "boom-bust" dynamic, fluctuating between rare environmental states and occasional proliferation. Although direct environmental drivers remain unresolved, emerging trends with macroalgal cover and reef productivity highlight the potential influence of ecosystem conditions on ciliate abundance. This work broadens the understanding of how marine pathogens persist between outbreaks and underscores the importance of environmental surveillance for predicting and mitigating future disease events on coral reefs.

microbiology↗

bioRxiv2025

Scuticociliate Detection and Microbiome Composition in Museum Collections of Diadema Antillarum

BackgroundThe mass mortality of the long-spined sea urchin Diadema antillarum has caused widespread ecological changes across Caribbean reefs, with recent studies identifying the etiological agent as pathogenic ciliate designated as a D. antillarum Scuticociliatosis Philaster-clade (DaScPc). The origin and ecological trajectory of DaScPc remain unresolved, raising critical questions about whether it represents a novel introduction or a resident commensal symbiont that transitioned into pathogenicity. MethodsTo address this, we tested 50 individual preserved museum specimens of D. antillarum collected between 1960 and 2020, with targeted PCR amplification of ciliate 18S, 28S, and 5.8S/ITS rRNA genes for spine, body wall, and coelomic fluid samples (n=100). Following up on recent work that identified bacterial biomarkers of DaSc, we also characterized the microbial communities associated with these museum specimens using 16S rRNA amplicon sequencing. Results. Our results reveal the presence of identical DaScPc 18S rRNA sequences in 21% of tested samples, 28S rRNA PCR yielded sequences at 96-98 % nt identity in only 2% of the tested samples, and we got no amplification from the 5.8S/ITS region. While these findings suggest possible long-term persistence or repeated emergence of this ciliate, the lack of 28S rRNA matches and lack of detection of ITS2 demonstrates that DaScPc 18S rRNA gene detections may be false positives for the ciliate over a highly conserved rRNA region. The microbial composition of the samples didnt yield any of the previously identified disease-associated bacterial biomarkers and showed large shifts in the overall microbial community based on collection period and the facility where the samples are housed. This study demonstrates that museum-preserved echinoderm tissues retain ecologically informative microbial DNA and establishes a molecular framework for disentangling pathogen provenance and its caveats. It also highlights the value and limitations of natural history collections in reconstructing marine disease ecology.

microbiology↗

bioRxiv2025

When bacteria meet many arms: Autecological insights into Vibrio pectinicida FHCF-3 in echinoderms

Sea star wasting (SSW) has been described globally in over 25 species of asteroids. This condition is characterized by body wall lesions, loss of turgor and ray autotomy, which often results in the mortality of specimens. The cause of SSW has remained elusive. A recent report detailing a potential causative agent, Vibrio pectenicida FHCF-3 (Prentice et al., 2025), inspired an investigation into its occurrence in available genomic and transcriptomic data from 2013-2015 from wild specimens and those enrolled in experimental incubations. While Vibrio pectenicida FHCF-3 16S rRNA gene sequences were detected in abnormal body wall tissues of Pycnopodia helianthoides from public aquaria in 2013, they were not detected in grossly normal or abnormal body wall specimens of other species sampled concurrently at sites where mass mortality was observed and from public aquaria. Experimental amendment of Pisaster ochraceus with organic matter substrates led to enrichment of V. pectenicida FHCF-3 16S rRNAs at the animal-water interface, and that they surged in abundance 24h prior to body wall lesion appearance. However, in this experiment V. pectenicida FHCF-3 16S rRNAs were inconsistently detected in coelomic fluid of abnormal specimens, and their abundance at specimen surfaces was inversely related to coelomic fluid detections. Perplexingly, V. pectenicida FHCF-3 was detected in abnormal P. helianthoides treated with 0.2 {micro}m filtrates of homogenized tissues, but absent in grossly normal heat-treated filtrate controls in prior work. Vibrio spp, are copiotrophs that experience rapid growth to dominate microbial communities in plankton and tissues when amended to seawater in a mesocosm experiment. These patterns indicate V. pectenicida FHCF-3 might cause abnormalities in P. helianthoides under certain conditions, but its growth might be a secondary rather than primary determinant of disease (i.e. it is saprobic or an opportunistic agent). It remains possible that sea star wasting abnormalities in P. helianthoides represent a generalized response to bacterial infiltration, driven by a diverse set of bacteria which includes but does not require species such as V. pectenicida FHCF-3. Finally, our data suggest that this taxon is not intimately tied to SSW abnormalities in other species. Hence, V. pectenicida FHCF-3 may be a driver of a SSW disease in P. heliathoides, but cannot be the cause of all SSW across species.

microbiology↗

bioRxiv2023

Transglobal spread of an ecologically significant sea urchin parasite

Mass mortality of the dominant coral reef herbivore Diadema antillarum in the Caribbean in the early 1980s led to a persistent phase shift from coral-to algal-dominated reefs. In 2022, a scuticociliate most closely related to Philaster apodigitiformis caused further mass mortality of D. antillarum across the Caribbean, leading to >95% mortality at affected sites. Mortality was also reported in the related species Diadema setosum in the Mediterranean in 2022, where urchins experienced gross signs compatible with scuticociliatosis. However, the causative agent of the Mediterranean outbreak has not yet been determined. In April 2023, mass mortality of D. setosum occurred along the Sultanate of Omans coastline. Urchins displayed signs compatible with scuticociliatosis including abnormal behavior, drooping and loss of spines, followed by tissue necrosis and death. Here we report the detection of an 18S rRNA gene sequence in abnormal urchins from Muscat, Oman that is identical to the Philaster strain responsible for D. antillarum mass mortality in the Caribbean. We also show that scuticociliatosis signs can be elicited in D. setosum by experimental challenge with the cultivated Philaster strain associated with Caribbean scuticociliatosis. These results demonstrate the Philaster sp. associated with D. antillarum mass mortality has rapidly spread to geographically distant coral reefs, compelling global-scale awareness and monitoring for this devastating condition through field surveys, microscopy, and molecular microbiological approaches, and prompting investigation of long-range transmission mechanisms.

ecology↗

bioRxiv2023

Design and validation of a PCR protocol to specifically detect the clade of Philaster sp. associated with Diadema antillarum scuticociliatosis

Diadema antillarum scuticociliatosis (DaSc), caused by a scuticociliate closely related to Philaster apodigitiformis, has affected Caribbean long-spined urchins since at least January 2022. Quantitative PCR (qPCR) is currently the standard method for detection of this ciliate in tissue and coelomic fluid samples, yet this method requires specialized equipment and is more expensive than standard PCR methods. The DaSc scuticociliate occurs against a backdrop of endo- and ecto-symbiotic ciliates which complicate detection using universal or pan-phylum PCR primer sets. To overcome these limitations, we designed and validated a sensitive and specific PCR primer (scutico-634F) and nested two-step PCR protocol to detect this taxon, which excludes other ciliates associated with D. antillarum and has poor affinity for other related ciliates. This primer and protocol for the DaSc-associated Philaster clade (DaScPc) allow for widely-accessible investigation of this pathogen in new regions and within environmental reservoirs.

microbiology↗

bioRxiv2022

The RNA Virome of Echinoderms

Echinoderms are a phylum of marine invertebrates that include model organisms, keystone species, and animals commercially harvested for seafood. Despite their scientific, ecological, and economic importance, there is little known about the diversity of RNA viruses that infect echinoderms compared to other invertebrates. We screened over 900 transcriptomes and viral metagenomes to characterize the RNA virome of 38 echinoderm species from all five classes (Crinoidea, Holothuroidea, Asteroidea, Ophiuroidea and Echinoidea). We identified 347 viral genome fragments that were classified to genera and families within nine viral orders - Picornavirales, Durnavirales, Martellivirales, Nodamuvirales, Reovirales, Amarillovirales, Ghabrivirales, Mononegavirales, and Hepelivirales. We compared the relative viral representation across three life stages (embryo, larvae, adult) and characterized the gene content of contigs which encoded complete or near-complete genomes. The proportion of viral reads in a given transcriptome was not found to significantly differ between life stages though the majority of viral contigs were discovered from transcriptomes of adult tissue. This study illuminates the biodiversity of RNA viruses from echinoderms, revealing the occurrence of viral groups in natural populations.

microbiology↗

bioRxiv2020

Surveillance of densoviruses and mesomycetozoans inhabiting grossly normal tissues of three New Zealand asteroid species

Asteroid wasting events and mass mortality have occurred for over a century. We currently lack a fundamental understanding of the microbial ecology of asteroid disease, with disease investigations hindered by sparse information about the microorganisms associated with grossly normal specimens. We surveilled viruses and protists associated with grossly normal specimens of three asteroid species (Patiriella regularis, Stichaster australis, Coscinasterias muricata) on the North Island, New Zealand, using metagenomes prepared from virus and ribosome-sized material. We discovered several densovirus-like genome fragments in our RNA and DNA metagenomic libraries. Subsequent survey of their prevalence within populations by quantitative PCR (qPCR) demonstrated their occurrence in only a few (13 %) specimens (n = 36). Survey of large and small subunit rRNAs in metagenomes revealed the presence of a mesomycete (most closely matching Ichthyosporea sp.). Survey of large subunit prevalence and load by qPCR revealed that it is widely detectable (80%) and present predominately in body wall tissues across all 3 species of asteroid. Our results raise interesting questions about the roles of these microbiome constituents in host ecology and pathogenesis under changing ocean conditions.

microbiology↗

bioRxiv2019

A highly prevalent and pervasive densovirus discovered among sea stars from the North American Atlantic Coast

Viral metagenomes prepared from tissues from Forbes sea star (Asterias forbesi) led to the discovery of a complete genome of a novel sea star densovirus (AfaDV). The genome organization of AfaDV and phylogenetic analysis place this virus among the Ambidensovirus genus in the subfamily Densoviridae, family Parvoviridae. AfaDV shares 78% nucleotide pairwise identity to the sea star associated densovirus (SSaDV), previously described as the putative causative agent of Sea Star Wasting Syndrome among sea stars from the Northwest Pacific. SSaDV was not found in specimens collected in this study, and the discovery of AfaDV might explain previous reports of SSaDV among sea stars from the Atlantic Coast. A qPCR assay was designed to assess tissue tropism, host specificity, and prevalence of AfaDV among wild populations of sea stars at five locations on the North American Atlantic Coast. AfaDV was detected in all three common sea star species (Asterias forbesi, Asterias rubens, and Henricia sp.) found in the region and was highly prevalent (80-100% of individuals tested, n=134), among populations collected at disparate sites 7 years apart. AfaDV was detected in the body wall, gonads, and pyloric caeca (digestive gland) of specimens but was not detected in their coelomic fluid. A significant difference in viral load was found between tissue types with the pyloric caeca having the highest viral load suggesting it is the primary site of viral replication in the animal. Further investigation of Asterias forbesi gonad tissue found germline cells (oocytes) to be virus positive suggesting a potential route of vertical transmission. Taken together, these observations show that the presence AfaDV is not an indicator of Sea Star Wasting Syndrome because AfaDV is a common constituent of these animals microbiome, regardless of health. These results broaden the understanding of echinoderm densoviruses outside the context of disease that suggest these viruses might form commensal or mutualistic relationships with their hosts.

microbiology↗

bioRxiv2019

The virome in adult monozygotic twins with concordant or discordant gut microbiomes

The virome is one of the most variable components of the human gut microbiome. Within twin-pairs, viromes have been shown to be similar for infants but not for adults, indicating that as twins age and their environments and microbiomes diverge, so do their viromes. The degree to which the microbiome drives the viromes vast diversity is unclear. Here, we examined the relationship between microbiome diversity and virome diversity in 21 adult monozygotic twin pairs selected for high or low microbiome concordance. Viromes derived from virus-like particles were unique to each subject, dominated by Caudovirales and Microviridae, and exhibited a small core that included crAssphage. Microbiome-discordant twins had more dissimilar viromes compared to microbiome-concordant twins, and the richer the microbiomes, the richer the viromes. These patterns were driven by the bacteriophages, not eukaryotic viruses. These observations support a strong role of the microbiome in patterning the virome.

microbiology↗