Vibrio owensii induces the tissue loss disease Montipora white syndrome in the Hawaiian reef coral Montipora capitata

Trade-off between photosymbiosis and innate immunity influences cnidarian's response to pathogenic bacteria

Mutualistic relationships with photosynthetic organisms are common in cnidarians, which form an intracellular symbiosis with dinoflagellates in the family Symbiodiniaceae. The establishment and maintenance of these symbionts are associated with the suppression of key host immune factors. Because of this, there are potential trade-offs between the nutrition that cnidarian hosts gain from their symbionts and their ability to successfully defend themselves from pathogens. To investigate these potential trade-offs, we utilized the facultatively symbiotic polyps of the upside-down jellyfish Cassiopea xamachana and exposed aposymbiotic and symbiotic polyps to the pathogen Serratia marcescens. Symbiotic polyps had a lower probability of survival following S. marcescens exposure. Gene expression analyses 24 hours following pathogen exposure indicate that symbiotic animals mounted a more damaging immune response, with higher levels of inflammation and oxidative stress likely resulting in more severe disruptions to cellular homeostasis. Underlying this more damaging immune response may be differences in constitutive and pathogen-induced expression of immune transcription factors between aposymbiotic and symbiotic polyps rather than broadscale immune suppression during symbiosis. Our findings indicate that in facultatively symbiotic polyps, hosting symbionts limits C. xamachana's ability to survive pathogen exposure, indicating a trade-off between symbiosis and immunity that has potential implications for coral disease research.

Evaluating the coral microbiome during cryopreservation

Coral reefs are threatened by various local and global stressors, including elevated ocean temperatures due to anthropogenic climate change. Coral cryopreservation could help secure the diversity of threatened corals. Recently, isochoric vitrification was used to demonstrate that coral fragments lived to 24 hr post-thaw; however, in this study, they were stressed post-thaw. The microbial portion of the coral holobiont has been shown to affect host fitness and the impact of cryopreservation treatment on coral microbiomes is unknown. Therefore, we examined the coral-associated bacterial communities pre- and post-cryopreservation treatments, with a view towards informing potential future stress reduction strategies. We characterized the microbiome of the Hawaiian finger coral, Porites compressa in the wild and at seven steps during the isochoric vitrification process. We observed significant changes in microbiome composition, including: 1) the natural wild microbiomes of P. compressa were dominated by Endozoicomonadaceae (76.5 % relative abundance) and consistent between samples, independent of collection location across Kāne'ohe Bay; 2) Endozoicomonadaceae were reduced to <6.9 % in captivity, and further reduced to <0.5 % relative abundance after isochoric vitrification; and 3) Vibrionaceae dominated communities post-thaw (58.5-74.7 % abundance). Thus, the capture and cryopreservation processes, are implicated as possible causal agents of dysbiosis characterized by the loss of putatively beneficial symbionts (Endozoicomonadaceae) and overgrowth of potential pathogens (Vibrionaceae). Offsetting these changes with probiotic restoration treatments may alleviate cryopreservation stress and improve post-thaw husbandry.

Novel metagenomics analysis of stony coral tissue loss disease

Stony coral tissue loss disease (SCTLD) has devastated coral reefs off the coast of Florida and continues to spread throughout the Caribbean. Although a number of bacterial taxa have consistently been associated with SCTLD, no pathogen has been definitively implicated in the etiology of SCTLD. Previous studies have predominantly focused on the prokaryotic community through 16S rRNA sequencing of healthy and affected tissues. Here, we provide a different analytical approach by applying a bioinformatics pipeline to publicly available metagenomic sequencing samples of SCTLD lesions and healthy tissues from 4 stony coral species. To compensate for the lack of coral reference genomes, we used data from apparently healthy coral samples to approximate a host genome and healthy microbiome reference. These reads were then used as a reference to which we matched and removed reads from diseased lesion tissue samples, and the remaining reads associated only with disease lesions were taxonomically classified at the DNA and protein levels. For DNA classifications, we used a pathogen identification protocol originally designed to identify pathogens in human tissue samples, and for protein classifications, we used a fast protein sequence aligner. To assess the utility of our pipeline, a species-level analysis of a candidate genus, Vibrio, was used to demonstrate the pipeline's effectiveness. Our approach revealed both complementary and unique coral microbiome members compared with a prior metagenome analysis of the same dataset.

Microbial and transcriptional response of Acropora valida and Turbinaria peltata to Vibrio coralliilyticus challenge: insights into corals disease resistance

BACKGROUND

Coral diseases are significant drivers of global coral reef degradation, with pathogens dominated by Vibrio coralliilyticus playing a prominent role in the development of coral diseases. Coral phenotype, symbiotic microbial communities, and host transcriptional regulation have been well-established as factors involved in determining coral disease resistance, but the underlying mechanisms remain incompletely understood.

METHODS

This study employs high-throughput sequencing to analyse the symbiotic microbial and transcriptional response of the hosts in order to evaluate the disease resistance of Acropora valida and Turbinaria peltata exposed to Vibrio coralliilyticus.

RESULTS

A. valida exhibited pronounced bleaching and tissue loss within 7 h of pathogen infection, whereas T. peltata showed no signs of disease throughout the experiment. Microbial diversity analyses revealed that T. peltata had a more flexible microbial community and a higher relative abundance of potential beneficial bacteria compared to A. valida. Although Vibrio inoculation resulted in a more significant decrease in the Symbiodiniaceae density of A. valida compared to that of T. peltata, it did not lead to recombination of the coral host and Symbiodiniaceae in either coral species. RNA-seq analysis revealed that the interspecific differences in the transcriptional regulation of hosts after Vibrio inoculation. Differentially expressed genes in A. valida were mainly enriched in the pathways associated with energy supply and immune response, such as G protein-coupled receptor signaling, toll-like receptor signaling, regulation of TOR signaling, while these genes in T. peltata were mainly involved in the pathway related to immune homeostasis and ion transport, such as JAK-STAT signaling pathway and regulation of ion transport.

CONCLUSIONS

Pathogenic challenges elicit different microbial and transcriptional shifts across coral species. This study offers novel insights into molecular mechanisms of coral resistance to disease.

Impact of Nutrient Enrichment on Community Structure and Co-Occurrence Networks of Coral Symbiotic Microbiota in Duncanopsammia peltata: Zooxanthellae, Bacteria, and Archaea

Symbiotic microorganisms in reef-building corals, including algae, bacteria, archaea, fungi, and viruses, play critical roles in the adaptation of coral hosts to adverse environmental conditions. However, their adaptation and functional relationships in nutrient-rich environments have yet to be fully explored. This study investigated Duncanopsammia peltata and the surrounding seawater and sediments from protected and non-protected areas in the summer and winter in Dongshan Bay. High-throughput sequencing was used to characterize community changes, co-occurrence patterns, and factors influencing symbiotic coral microorganisms (zooxanthellae, bacteria, and archaea) in different environments. The results showed that nutrient enrichment in the protected and non-protected areas was the greatest in December, followed by the non-protected area in August. In contrast, the August protected area had the lowest nutrient enrichment. Significant differences were found in the composition of the bacterial and archaeal communities in seawater and sediments from different regions. Among the coral symbiotic microorganisms, the main dominant species of zooxanthellae is the C1 subspecies (42.22-56.35%). The dominant phyla of bacteria were Proteobacteria, Cyanobacteria, Firmicutes, and Bacteroidota. Only in the August protected area did a large number (41.98%) of SAR324_cladeMarine_group_B exist. The August protected and non-protected areas and December protected and non-protected areas contained beneficial bacteria as biomarkers. They were Nisaea, Spiroplasma, Endozoicomonas, and Bacillus. No pathogenic bacteria appeared in the protected area in August. The dominant phylum in Archaea was Crenarchaeota. These symbiotic coral microorganisms' relative abundances and compositions vary with environmental changes. The enrichment of dissolved inorganic nitrogen in environmental media is a key factor affecting the composition of coral microbial communities. Co-occurrence analysis showed that nutrient enrichment under anthropogenic disturbances enhanced the interactions between coral symbiotic microorganisms. These findings improve our understanding of the adaptations of coral holobionts to various nutritional environments.

AI-2 quorum sensing signal disrupts coral symbiotic homeostasis and induces host bleaching

Symbiotic microorganisms play critical ecophysiological roles that facilitate the maintenance of coral health. Currently, information on the gene and protein pathways contributing to bleaching responses is lacking, including the role of autoinducers. Although the autoinducer AI-1 is well understood, information on AI-2 is insufficient. Here, we observed a 3.7-4.0 times higher abundance of the AI-2 synthesis gene luxS in bleached individuals relative to their healthy counterparts among reef-building coral samples from the natural environment. Laboratory tests further revealed that AI-2 contributed significantly to an increase in coral bleaching, altered the ratio of potential probiotic and pathogenic bacteria, and suppressed the antiviral activity of specific pathogenic bacteria while enhancing their functional potential, such as energy metabolism, chemotaxis, biofilm formation and virulence release. Structural equation modeling indicated that AI-2 influences the microbial composition, network structure, and pathogenic features, which collectively contribute to the coral bleaching status. Collectively, our results offer novel potential strategies for coral conservation based on a signal manipulation approach.

Genome sequence of Alteromonas macleodii strain OCN004 isolated from the extracellular mucus of an apparently healthy rice coral (Montipora capitata)

Alteromonas macleodii strain OCN004, a marine gammaproteobacterium in the Alteromonadaceae family, has primarily been studied as a non-pathogenic negative control bacterium during laboratory infection trials to test the virulence of bacterial coral pathogens. The draft genome sequence of A. macleodii strain OCN004 is presented here.

Fluctibacter corallii gen. nov., sp. nov., isolated from the coral Montipora capitata on a reef in Kāne'ohe Bay, O'ahu, Hawai'i, reclassification of Aestuariibacter halophilus as Fluctibacter halophilus comb. nov., and Paraglaciecola oceanifecundans as a later heterotypic synonym of Paraglaciecola agarilytica

Strain AA17T was isolated from an apparently healthy fragment of Montipora capitata coral from the reef surrounding Moku o Lo'e in Kāne'ohe Bay, O'ahu, Hawai'i, USA, and was taxonomically evaluated using a polyphasic approach. Comparison of a partial 16S rRNA gene sequence found that strain AA17T shared the greatest similarity with Aestuariibacter halophilus JC2043T (96.6%), and phylogenies based on 16S rRNA gene sequences grouped strain AA17T with members of the Aliiglaciecola, Aestuariibacter, Lacimicrobium, Marisediminitalea, Planctobacterium, and Saliniradius genera. To more precisely infer the taxonomy of strain AA17T, a phylogenomic analysis was conducted and indicated that strain AA17T formed a monophyletic clade with A. halophilus JC2043T, divergent from Aestuariibacter salexigens JC2042T and other related genera. As a result of monophyly and multiple genomic metrics of genus demarcation, strain AA17T and A. halophilus JC2043T comprise a distinct genus for which the name Fluctibacter gen. nov. is proposed. Based on a polyphasic characterisation and identifying differences in genomic and taxonomic data, strain AA17T represents a novel species, for which the name Fluctibacter corallii sp. nov. is proposed. The type strain is AA17T (= LMG 32603 T = NCTC 14664T). This work also supports the reclassification of A. halophilus as Fluctibacter halophilus comb. nov., which is the type species of the Fluctibacter genus. Genomic analyses also support the reclassification of Paraglaciecola oceanifecundans as a later heterotypic synonym of Paraglaciecola agarilytica.

Bacterial pathogens associated with the plastisphere of surgical face masks and their dispersion potential in the coastal marine environment

Huge numbers of face masks (FMs) were discharged into the ocean during the coronavirus pandemic. These polymer-based artificial surfaces can support the growth of specific bacterial assemblages, pathogens being of particular concern. However, the potential risks from FM-associated pathogens in the marine environment remain poorly understood. Here, FMs were deployed in coastal seawater for two months. PacBio circular consensus sequencing of the full-length 16S rRNA was used for pathogen identification, providing enhanced taxonomic resolution. Selective enrichment of putative pathogens (e.g., Ralstonia pickettii) was found on FMs, which provided a new niche for these pathogens rarely detected in the surrounding seawater or the stone controls. The total relative abundance of the putative pathogens in FMs was higher than in seawater but lower than in the stone controls. FM exposure during the two months resulted in 3% weight loss and the release of considerable amounts of microfibers. The ecological assembly process of the putative FM-associated pathogens was less impacted by the dispersal limitation, indicating that FM-derived microplastics can serve as vectors of most pathogens for their regional transport. Our results indicate a possible ecological risk of FMs for marine organisms or humans in the coastal and potentially in the open ocean.

Antimicrobial and quorum sensing inhibitory activity of epiphytic bacteria isolated from the red alga Halymenia durvillei

Halymenia durvillei is a red alga that is commonly utilized in the Philippines as food and as a source of high-value natural products for industrial applications. However, there are no studies regarding the microbial community associated with H. durvillei and its potential applications. This study aimed to isolate and identify the epiphytic bacteria of H. durvillei and determine their antimicrobial and quorum sensing inhibitory (QSI) effects. The thalli of H. durvillei were collected at the shores of Santa Fe, Bantayan, Cebu, Philippines. Bacterial isolates were identified using 16S rRNA, and their ethyl acetate (EtOAc) extracts were subjected to antimicrobial susceptibility tests against representative species of yeast and Gram-negative and Gram-positive bacteria. Their QSI activity against Chromobacterium violaceum was also determined. Fourteen distinct bacterial colonies belonging to four genera, namely Alteromonas (3), Bacillus (5), Oceanobacillus (1) and Vibrio (5), were successfully isolated and identified. All 14 bacterial isolates exhibited antibacterial effects. EPB9, identified as Bacillus safensis , consistently showed the strongest inhibition against Escherichia coli , Staphylococcus aureus and Staphylococcus epidermidis , with minimum inhibitory concentrations (MICs) ranging from 0.0625 to 1.0 mg ml-1. In contrast, all 14 isolates showed weak antifungal effects. Both B. safensis (EPB9) and Bacillus australimaris (EPB15) exhibited QSI effects at 100 mg ml-1, showing opaque zones of 3.1±0.9 and 3.8±0.4 mm, respectively. This study is the first to isolate and identify the distinct microbial epiphytic bacterial community of H. durvillei and its potential as an abundant resource for new antibacterial and QSI bioactives.

Mass mortality of the keratose sponge Sarcotragus foetidus in the Aegean Sea (Eastern Mediterranean) correlates with proliferation of Vibrio bacteria in the tissues

In the last two decades, episodes of mass mortality in benthic communities have often been associated with climatic anomalies, but the ultimate mechanisms through which they lead to death have rarely been identified. This study reports a mass mortality of wild sponges in the Aegean Sea (Turkey, Eastern Mediterranean), which affected the keratose demosponge Sarcotragus foetidus in September 2021. We examined the occurrence of thermo-dependent bacteria of the genus Vibrio in the sponges, identified through 16S rRNA of colonies isolated from sponge tissue in specific culturing media. Six Vibrio sequences were identified from the sponges, three of them being putatively pathogenic (V. fortis, V. owensii, V. gigantis). Importantly, those Vibrios were isolated from only tissues of diseased sponges. In contrast, healthy individuals sampled in both summer and winter led to no Vibrio growth in laboratory cultures. A 50 years record of sea surface temperature (SST) data for the study area reveals a progressive increase in temperature from 1970 to 2021, with values above 24°C from May to September 2021, reaching an absolute historical maximum of 28.9°C in August 2021. We hypothesize that such elevated SST values maintained for several months in 2021 promoted proliferation of pathogenic Vibrio species (thermo-dependent bacteria) in S. foetidus, triggering or aggravating the course of sponge disease. Thus, vibrioisis emerges as one of the putative mechanisms through which global water warming in the Mediterranean Sea translates into sponge mortality. The historical time course of temperature data for the studied area in the Aegean Sea predicts that recurrent waves of elevated SST are likely to occur in the coming summers. If so, recurrent disease may eventually eliminate this abundant sponge from the sublittoral in the midterm, altering the original bathymetric distribution of the species and compromising its ecological role.

Coral Disease and Ingestion: Investigating the Role of Heterotrophy in the Transmission of Pathogenic Vibrio spp. using a Sea Anemone (Exaiptasia pallida) Model System

Understanding disease transmission in corals can be complicated given the intricacy of the holobiont and difficulties associated with ex situ coral cultivation. As a result, most of the established transmission pathways for coral disease are associated with perturbance (i.e., damage) rather than evasion of immune defenses. Here, we investigate ingestion as a potential pathway for the transmission of coral pathogens that evades the mucus membrane. Using sea anemones (Exaiptasia pallida) and brine shrimp (Artemia sp.) to model coral feeding, we tracked the acquisition of the putative pathogens, Vibrio alginolyticus, V. harveyi, and V. mediterranei using GFP-tagged strains. Vibrio sp. were provided to anemones using 3 experimental exposures (i) direct water exposure alone, (ii) water exposure in the presence of a food source (non-spiked Artemia), and (iii) through a "spiked" food source (Vibrio-colonized Artemia) created by exposing Artemia cultures to GFP-Vibrio via the ambient water overnight. Following a 3 h feeding/exposure duration, the level of acquired GFP-Vibrio was quantified from anemone tissue homogenate. Ingestion of spiked Artemia resulted in a significantly greater burden of GFP-Vibrio equating to an 830-fold, 3,108-fold, and 435-fold increase in CFU mL-1 when compared to water exposed trials and a 207-fold, 62-fold, and 27-fold increase in CFU mL-1 compared to water exposed with food trials for V. alginolyticus, V. harveyi, and V. mediterranei, respectively. These data suggest that ingestion can facilitate delivery of an elevated dose of pathogenic bacteria in cnidarians and may describe an important portal of entry for pathogens in the absence of perturbing conditions. IMPORTANCE The front line of pathogen defense in corals is the mucus membrane. This membrane coats the surface body wall creating a semi-impermeable layer that inhibits pathogen entry from the ambient water both physically and biologically through mutualistic antagonism from resident mucus microbes. To date, much of the coral disease transmission research has been focused on mechanisms associated with perturbance of this membrane such as direct contact, vector lesions (predation/biting), and waterborne exposure through preexisting lesions. The present research describes a potential transmission pathway that evades the defenses provided by this membrane allowing unencumbered entry of bacteria as in association with food. This pathway may explain an important portal of entry for emergence of idiopathic infections in otherwise healthy corals and can be used to improve management practices for coral conservation.

Concordance of microbial and visual health indicators of white-band disease in nursery reared Caribbean coral Acropora cervicornis

Background

Coral diseases are one of the leading causes of declines in coral populations. In the Caribbean, white band disease (WBD) has led to a substantial loss of Acropora corals. Although the etiologies of this disease have not been well described, characterizing the coral microbiome during the transition from a healthy to diseased state is critical for understanding disease progression. Coral nurseries provide unique opportunities to further understand the microbial changes associated with diseased and healthy corals, because corals are monitored over time. We characterized the microbiomes before and during an outbreak of WBD in Acropora cervicornis reared in an ocean nursery in Little Cayman, CI. We asked (1) do healthy corals show the same microbiome over time (before and during a disease outbreak) and (2) are there disease signatures on both lesioned and apparently healthy tissues on diseased coral colonies?

Methods

Microbial mucus-tissue slurries were collected from healthy coral colonies in 2017 (before the disease) and 2019 (during the disease onset). Diseased colonies were sampled at two separate locations on an individual coral colony: at the interface of Disease and ∼10 cm away on Apparently Healthy coral tissue. We sequenced the V4 region of the 16S rRNA gene to characterize bacterial and archaeal community composition in nursery-reared A. cervicornis. We assessed alpha diversity, beta diversity, and compositional differences to determine differences in microbial assemblages across health states (2019) and healthy corals between years (2017 and 2019).

Results

Microbial communities from healthy A. cervicornis from 2017 (before disease) and 2019 (after disease) did not differ significantly. Additionally, microbial communities from Apparently Healthy samples on an otherwise diseased coral colony were more similar to Healthy colonies than to the diseased portion on the same colony for both alpha diversity and community composition. Microbial communities from Diseased tissues had significantly higher alpha diversity than both Healthy and Apparently Healthy tissues but showed no significant difference in beta-diversity dispersion. Our results show that at the population scale, Healthy and Apparently Healthy coral tissues are distinct from microbial communities associated with Diseased tissues. Furthermore, our results suggest stability in Little Cayman nursery coral microbiomes over time. We show healthy Caymanian nursery corals had a stable microbiome over a two-year period, an important benchmark for evaluating coral health via their microbiome.

The coral microbiome: towards an understanding of the molecular mechanisms of coral-microbiota interactions

Corals live in a complex, multipartite symbiosis with diverse microbes across kingdoms, some of which are implicated in vital functions, such as those related to resilience against climate change. However, knowledge gaps and technical challenges limit our understanding of the nature and functional significance of complex symbiotic relationships within corals. Here, we provide an overview of the complexity of the coral microbiome focusing on taxonomic diversity and functions of well-studied and cryptic microbes. Mining the coral literature indicate that while corals collectively harbour a third of all marine bacterial phyla, known bacterial symbionts and antagonists of corals represent a minute fraction of this diversity and that these taxa cluster into select genera, suggesting selective evolutionary mechanisms enabled these bacteria to gain a niche within the holobiont. Recent advances in coral microbiome research aimed at leveraging microbiome manipulation to increase coral's fitness to help mitigate heat stress-related mortality are discussed. Then, insights into the potential mechanisms through which microbiota can communicate with and modify host responses are examined by describing known recognition patterns, potential microbially derived coral epigenome effector proteins and coral gene regulation. Finally, the power of omics tools used to study corals are highlighted with emphasis on an integrated host-microbiota multiomics framework to understand the underlying mechanisms during symbiosis and climate change-driven dysbiosis.

Use and Evaluation of a pES213-Derived Plasmid for the Constitutive Expression of gfp Protein in Pathogenic Vibrios: a Tagging Tool for In Vitro Studies

Insertion of green fluorescent protein (GFP) into bacterial cells for constitutive expression is a powerful tool for the localization of species of interest within complex mixtures. Here, we demonstrate and evaluate the efficacy of the pES213-derived donor plasmid pVSV102 (gfp Knr) as a conjugative tool for the tagging of Vibrio and related species (termed vibrios). Using a triparental mating assay assisted by the helper plasmid pEVS104 (tra trb Knr), we successfully tagged 12 species within the Vibrionaceae family representing 8 of the proposed clades. All transconjugant strains demonstrated bright fluorescence and were readily differentiable within complex mixtures of nontagged cells. Plasmid retention was assessed using persistence and subculture experimentation. Persistence experiments evaluated plasmid loss over time for nonsubcultured samples inoculated into antibiotic-free media and sterile artificial seawater, whereas subculture trials evaluated plasmid loss following one to four subculture passages. Strong plasmid retention (≥80%) was observed in persistence experiments for all transconjugant strains for up to 48 h in both antibiotic-free media and artificial seawater with the exception of Vibrio cholerae, which showed a substantial decline in media after 24 h. Subculturing experiments also demonstrated strong plasmid stability, with all transconjugant strains showing ≥80% retention after four subculture passages. The results of this research suggest that pVSV102 is a stable GFP plasmid for the tagging of a broad range of vibrios. IMPORTANCE Prior research has suggested that the use of Aliivibrio fischeri-derived donor plasmids with the pES213 origin of replication may provide increased plasmid stability for the tagging of vibrios compared to Escherichia coli-derived p15A plasmids. Here, we present a structured protocol for conjugation-based tagging of vibrios using the pES213-derived plasmid pVSV102 and evaluate the plasmid stability of tagged strains. These methods and the resulting transconjugant strains provide important standardized tools to facilitate experimentation requiring the use of traceable vibrio strains. Furthermore, the determination of the species-specific plasmid stability provides an estimation of the anticipated level of plasmid loss under the given set of culture conditions. This estimation can be used to reduce the occurrence of experimental biases introduced by plasmid drift.

First report of yellow-banded tissue loss disease on coral reefs outside the Arabian/Persian Gulf

Coral disease is a major cause of coral reef degradation, yet many diseases remain understudied. Yellow-banded tissue loss disease (YBTLD) has a distinct gross lesion morphology and to date has only been reported from the Arabian/Persian Gulf; little else is known about the ecology of the disease. We report on the first occurrence of YBTLD outside of the Arabian/Persian Gulf at 2 sites (Laku Point, Narara Reef) within the Gulf of Kachchh (GoK) located on the northwest coast of India. At Narara Reef, YBTLD was observed at 12 out of 24 transects with an average prevalence of 4.7 ± 1.3%. At Laku Point, YBTLD was observed at 19 out of 24 transects with an average prevalence of 5.4 ± 1%. Four out of 15 coral genera within transects had signs of YBTLD and included Goniopora, Dipsastraea, Lobophyllia, and Turbinaria. Lobophyllia and Turbinaria had the highest susceptibility to the disease, with prevalence significantly higher than expected based on their abundance on the reefs. The distribution and prevalence of YBTLD in the GoK was higher than in coral reefs in the Arabian/Persian Gulf. The GoK is an extreme environment for coral reefs with both natural stressors (high salinities, strong, seasonal storm activities, and extreme tides) and anthropogenic pollutants from industrial, mining, agricultural, and domestic activities. These poor environmental conditions may help explain the high occurrence of YBTLD on GoK reefs.

Development of a real-time quantitative PCR assay for detection and quantification of the marine bacterium Alteromonas macleodii from coastal environments

Alteromonas macleodii is a ubiquitous marine bacterial species found in a variety of habitats that displays both planktonic and particle-associated lifestyles. Transcriptomic studies demonstrate that, even when present at low abundance, it can make significant contributions to biogeochemical cycles, and its specific association with key marine phytoplankton species indicates other ecological roles as well. It has also been shown to be one of the early colonizers of copper-treated marine vessels. There currently exist no rapid, reliable molecular assays for the detection and quantification of A. macleodii from its different environments. We developed a real-time PCR assay, specific to A. macleodii. This assay targets the DNA gyrase B subunit (gyrB) gene, which occurs as a single copy in the genome. The assay possesses an amplification efficiency of 94.3%, with a limit of detection of 2.5 gyrB copies per μL. Assay specificity was validated by melt curve analysis, followed by sequencing of the amplified product. The assay was specific to thirteen A. macleodii strains and did not amplify other marine bacteria, including Roseobacter denitrificans, Silicibacter sp. TM1040, Vibrio coralliilyticus, Vibrio harveyi, and Vibrio alginolyticus. It also did not amplify Alteromonas mediterranea, a close relative that can occur in the same environment as A. macleodii. This assay was used to determine the presence and abundance of A. macleodii from a range of coastal habitats. The assay was also used to monitor the A. macleodii growth in biofilm and planktonic cultures over time in the presence of elevated copper. This assay provides a rapid and reliable means to assess the presence and abundance of a ubiquitous marine bacterium that, even at low abundance, has been shown to make significant contributions to key marine processes.

Isolation and characterization of a Vibrio owensii phage phi50-12

Vibrio owensii is a widely distributed marine vibrio species that causes acute hepatopancreatic necrosis in the larvae of Panulirus ornatus and Penaeus vannamei, and is also associated with Montipora white syndrome in corals. We characterized V. owensii GRA50-12 as a potent pathogen using phenotypic, biochemical, and zebrafish models. A virulent phage, vB_VowP_phi50-12 (phi50-12), belonging to the N4-like Podoviridae, was isolated from the same habitat as that of V. owensii GRA50-12 and characterized. This phage possesses a unique sequence with no similar hits in the public databases and has a short latent time (30 min), a large burst size (106 PFU/infected cell), and a wide range of pH and temperature stabilities. Moreover, phi50-12 also demonstrated a strong lysis ability against V. owensii GRA50-12. SDS-PAGE revealed at least nine structural proteins, four of which were confirmed using LC–MS/MS analysis. The size of the phi50-12 genome was 68,059 bp, with 38.5% G + C content. A total of 101 ORFs were annotated, with 17 ORFs having closely related counterparts in the N4-like vibrio phage. Genomic sequencing confirmed the absence of antibiotic resistance genes or virulence factors. Comparative studies have shown that phi50-12 has a unique genomic arrangement, except for the well-conserved core regions of the N4-like phages. Phylogenetic analysis demonstrated that it belonged to a group of smaller genomes of N4-like vibrio phages. The therapeutic effect in the zebrafish model suggests that phi50-12 could be a potential candidate for application in the treatment of V. owensii infection or as a biocontrol agent. However, further research must be carried out to confirm the efficacy of phage50-12.

Intestinal Microbiome Richness of Coral Reef Damselfishes (Actinopterygii: Pomacentridae)

Fish gastro-intestinal system harbors diverse microbiomes that affect the host's digestion, nutrition, and immunity. Despite the great taxonomic diversity of fish, little is understood about fish microbiome and the factors that determine its structure and composition. Damselfish are important coral reef species that play pivotal roles in determining algae and coral population structures of reefs. Broadly, damselfish belong to either of two trophic guilds based on whether they are planktivorous or algae-farming. In this study, we used 16S rRNA gene sequencing to investigate the intestinal microbiome of 5 planktivorous and 5 algae-farming damselfish species (Pomacentridae) from the Great Barrier Reef. We detected Gammaproteobacteria ASVs belonging to the genus Actinobacillus in 80% of sampled individuals across the 2 trophic guilds, thus, bacteria in this genus can be considered possible core members of pomacentrid microbiomes. Algae-farming damselfish had greater bacterial alpha-diversity, a more diverse core microbiome and shared 35 ± 22 ASVs, whereas planktivorous species shared 7 ± 3 ASVs. Our data also highlight differences in microbiomes associated with both trophic guilds. For instance, algae-farming damselfish were enriched in Pasteurellaceae, whilst planktivorous damselfish in Vibrionaceae. Finally, we show shifts in bacterial community composition along the intestines. ASVs associated with the classes Bacteroidia, Clostridia, and Mollicutes bacteria were predominant in the anterior intestinal regions while Gammaproteobacteria abundance was higher in the stomach. Our results suggest that the richness of the intestinal bacterial communities of damselfish reflects host species diet and trophic guild.

Comparison of Vibrio coralliilyticus virulence in Pacific oyster larvae and corals

The bacterium Vibrio coralliilyticus has been implicated in mass mortalities of corals and shellfish larvae. However, using corals for manipulative infection experiments can be logistically difficult compared to other model organisms, so we aimed to establish oyster larvae infections as a proxy model. Therefore, this study assessed the virulence of six wild-type V. coralliilyticus strains, and mutants of one strain with deletions of known virulence factors, between Pacific oyster larvae (Crassostrea gigas) and Hawaiian rice coral (Montipora capitata) infection systems. The wild-type strains tested displayed variable virulence in each system, but virulence levels between hosts were not necessarily comparable. Strains RE98 and OCN008 maintained a medium to high level of virulence across hosts and appeared to be more generalist pathogens. Strain H1, in contrast, was avirulent towards coral but displayed a medium level of virulence towards oyster larvae. Interestingly, the BAA-450 type strain had a medium level of virulence towards coral and was the least virulent to oyster larvae. A comparison of known virulence factors determined that the flagellum, motility or chemotaxis, all of which play a significant role in coral infections, were not crucial for oyster infections with strain OCN008. A genomic comparison of the newly sequenced strain H1 with the other strains tested identified 16 genes potentially specific to coral pathogens that were absent in H1. This is both the first comparison of various V. coralliilyticus strains across infection systems and the first investigation of a strain that is non-virulent to coral. Our results indicate that the virulence of V. coralliilyticus strains in coral is not necessarily indicative of virulence in oyster larvae, and that the set of genes tested are not required for virulence in both model systems. This study increases our understanding of the virulence between V. coralliilyticus strains and helps assess their potential threat to marine environments and shellfish industries.

Thank you for biting: dispersal of beneficial microbiota through 'antagonistic' interactions

Multicellular organisms harbor populations of microbial symbionts; some of these symbionts can be dispersed through the feeding activities of consumers. Studies of consumer-mediated microbiota dispersal generally focus on pathogenic microorganisms; the dispersal of beneficial microorganisms has received less attention, especially in the context of 'antagonistic' trophic interactions (e.g., herbivory, parasitism, predation). Yet, this 'trophic transmission' of beneficial symbionts has significant implications for microbiota assembly and resource species (e.g., prey) health. For example, trophic transmission of microorganisms could assist with environmental acclimatization and help resource species to suppress other consumers or competitors. Here, we highlight model systems and approaches that have revealed these potential 'silver-linings' of antagonism as well as opportunities and challenges for future research.

Ciliated protozoan occurrence and association in the pathogenesis of coral disease

Various microbial infections have significantly contributed to disease progression leading to the mortality of corals. However, the holobiont and the external surfaces of coral, including the secreted mucus, provide a varied microenvironment that attracts ciliates based on their feeding preferences. Besides, some ciliates (e.g., Philasterine scuticociliate) may enter through the injuries or lesions on corals or through their indirect interactions with other types of microbes that influence coral health. Thus, ciliates occurrence and association are described with 12 different diseases worldwide. White syndrome disease lesions have diverse ciliate associations, and higher ciliate diversity was observed with diseased genera Acropora. Also, it was described, about sixteen ciliate species ingest coral Symbiodiniaceae and histophagous ciliates for coral tissue loss as secondary invaders. However, the ciliates nature of association with the coral disease remains unclear for primary or opportunistic secondary pathogenicity. Herein, we explore the urgent need to understand the complex interactions of ciliates in coral health.

Microbial bioindicators of Stony Coral Tissue Loss Disease identified in corals and overlying waters using a rapid field-based sequencing approach

Stony Coral Tissue Loss Disease (SCTLD) is a devastating disease. Since 2014, it has spread along the entire Florida Reef Tract and into the greater Caribbean. It was first detected in the United States Virgin Islands in January 2019. To more quickly identify microbial bioindicators of disease, we developed a rapid pipeline for microbiome sequencing. Over a span of 10 days we collected, processed and sequenced coral and near-coral seawater microbiomes from diseased and apparently healthy Colpophyllia natans, Montastraea cavernosa, Meandrina meandrites and Orbicella franksi. Analysis of bacterial and archaeal 16S ribosomal RNA gene sequences revealed 25 bioindicator amplicon sequence variants (ASVs) enriched in diseased corals. These bioindicator ASVs were additionally recovered in near-coral seawater (<5 cm of coral surface), a potential reservoir for pathogens. Phylogenetic analysis of microbial bioindicators with sequences from the Coral Microbiome Database revealed that Vibrio, Arcobacter, Rhizobiaceae and Rhodobacteraceae sequences were related to disease-associated coral bacteria and lineages novel to corals. Additionally, four ASVs (Algicola, Cohaesibacter, Thalassobius and Vibrio) were matches to microbes previously associated with SCTLD that should be targets for future research. Overall, this work suggests that a rapid sequencing framework paired with specialized databases facilitates identification of microbial disease bioindicators.

Characterization of the microbiome and immune response in corals with chronic Montipora white syndrome

Coral diseases have increased in frequency and intensity around the tropics worldwide. However, in many cases, little is known about their etiology. Montipora white syndrome (MWS) is a common disease affecting the coral Montipora capitata, a major reef builder in Hawai'i. Chronic Montipora white syndrome (cMWS) is a slow-moving form of the disease that affects M. capitata throughout the year. The effects of this chronic disease on coral immunology and microbiology are currently unknown. In this study, we use prophenoloxidase immune assays and 16S rRNA gene amplicon sequencing to characterize the microbiome and immunological response associated with cMWS. Our results show that immunological and microbiological responses are highly localized. Relative to diseased samples, apparently healthy portions of cMWS corals differed in immune activity and in the relative abundance of microbial taxa. Coral tissues with cMWS showed decreased tyrosinase-type catecholase and tyrosinase-type cresolase activity and increased laccase-type activity. Catecholase and cresolase activity were negatively correlated across all tissue types with microbiome richness. The localized effect of cMWS on coral microbiology and immunology is probably an important reason for the slow progression of the disease. This local confinement may facilitate interventions that focus on localized treatments on tissue types. This study provides an important baseline to understand the interplay between the microbiome and immune system and the mechanisms used by corals to manage chronic microbial perturbations associated with white syndrome.

Evaluating the feasibility and advantage of a multi-purpose submerged breakwater for harbor protection and benthic habitat enhancement at Kahului Commercial Harbor, Hawai‘i: case study

Construction of breakwaters provides an engineering solution for coastal protection. However, little effort has been made toward understanding the ecological impact on local coral reef ecosystems and developing engineering structures that would enhance the coral reef environment. A submerged breakwater proposed for Kahului Commercial Harbor, Hawai‘i, provided an opportunity to design a multi-purpose ‘reef structure’ to mitigate wave impacts while providing new coral reef habitat. This design involved ecological and environmental considerations alongside engineering principles, serving as a model for environmentally sound harbor development. This field study evaluated environmental conditions and reef community composition at the proposed site in a gradient extending outward from the harbor, using in situ data with multivariate analyses. Benthic and topographic features in the area were assessed using a towed drop camera system to relate to biological factors. Results that support breakwater topography should follow the natural spur and groove and depth of the adjacent reef and orient with wave direction. A deep area characterized by unconsolidated substrata and low coral cover would be replaced with the shallow, sloping hard bottom of the breakwater, and provide an exemplary area for corals to flourish while protecting the harbor from large ocean swells. Surfaces on shallow sloping hard bottoms receive higher levels of irradiance that benefits coral growth. Optimal levels of water motion facilitate sediment removal and promote coral recruitment and growth. The design of the Kahului Harbor submerged multi-purpose structure serves as a model for design of shoreline modification that enhances, rather than degrades, the local coral reef environment.

Deciphering Coral Disease Dynamics: Integrating Host, Microbiome, and the Changing Environment

Diseases of tropical reef organisms is an intensive area of study, but despite significant advances in methodology and the global knowledge base, identifying the proximate causes of disease outbreaks remains difficult. The dynamics of infectious wildlife diseases are known to be influenced by shifting interactions among the host, pathogen, and other members of the microbiome, and a collective body of work clearly demonstrates that this is also the case for the main foundation species on reefs, corals. Yet, among wildlife, outbreaks of coral diseases stand out as being driven largely by a changing environment. These outbreaks contributed not only to significant losses of coral species but also to whole ecosystem regime shifts. Here we suggest that to better decipher the disease dynamics of corals, we must integrate more holistic and modern paradigms that consider multiple and variable interactions among the three major players in epizootics: the host, its associated microbiome, and the environment. In this perspective, we discuss how expanding the pathogen component of the classic host-pathogen-environment disease triad to incorporate shifts in the microbiome leading to dysbiosis provides a better model for understanding coral disease dynamics. We outline and discuss issues arising when evaluating each component of this trio and make suggestions for bridging gaps between them. We further suggest that to best tackle these challenges, researchers must adjust standard paradigms, like the classic one pathogen-one disease model, that, to date, have been ineffectual at uncovering many of the emergent properties of coral reef disease dynamics. Lastly, we make recommendations for ways forward in the fields of marine disease ecology and the future of coral reef conservation and restoration given these observations.

Local Conditions Influence the Prokaryotic Communities Associated With the Mesophotic Black Coral Antipathella subpinnata

Black corals are important habitat-forming species in the mesophotic and deep-sea zones of the world’s oceans because of their arborescent colony structure and tendency to form animal forests. Although we have started unraveling the ecology of mesophotic black corals, the importance of the associated microbes to their health has remained unexplored. Here, we provide in-depth assessments of black coral-microbe symbioses by investigating the spatial and temporal stability of these associations, and make comparisons with a sympatric octocoral with similar colony structure. To this end, we collected samples of Antipathella subpinnata colonies from three mesophotic shoals situated along the Ligurian Coast of the Mediterranean Sea (Bordighera, Portofino, Savona) in the spring of 2017. At the Portofino shoal, samples of A. subpinnata and the gorgonian Eunicella cavolini were collected in November 2016 and May 2017. Bacterial communities were profiled using 16S rRNA gene amplicon sequencing. The bacterial community of E. cavolini was consistently dominated by Endozoicomonas. Contrastingly, the black coral microbiome was more diverse, and was primarily composed of numerous Bacteroidetes, Alpha- and Gammaproteobacterial taxa, putatively involved in all steps of the nitrogen and sulfur cycles. Compositional differences in the A. subpinnata microbiome existed between all locations and both time points, and no phylotypes were consistently associated with A. subpinnata. This highlights that local conditions may influence the bacterial community structure and potentially nutrient cycling within the A. subpinnata holobiont. But it also suggests that this coral holobiont possesses a high degree of microbiome flexibility, which may be a mechanism to acclimate to environmental change.

Disease Diagnostics and Potential Coinfections by Vibrio coralliilyticus During an Ongoing Coral Disease Outbreak in Florida

A deadly coral disease outbreak has been devastating the Florida Reef Tract since 2014. This disease, stony coral tissue loss disease (SCTLD), affects at least 22 coral species causing the progressive destruction of tissue. The etiological agents responsible for SCTLD are unidentified, but pathogenic bacteria are suspected. Virulence screens of 400 isolates identified four potentially pathogenic strains of Vibrio spp. subsequently identified as V. coralliilyticus. Strains of this species are known coral pathogens; however, cultures were unable to consistently elicit tissue loss, suggesting an opportunistic role. Using an improved immunoassay, the VcpA RapidTest, a toxic zinc-metalloprotease produced by V. coralliilyticus was detected on 22.3% of diseased Montastraea cavernosa (n = 67) and 23.5% of diseased Orbicella faveolata (n = 24). VcpA⁺ corals had significantly higher mortality rates and faster disease progression. For VcpA^- fragments, 21.6% and 33.3% of M. cavernosa and O. faveolata, respectively, died within 21 d of observation, while 100% of similarly sized VcpA⁺ fragments of both species died during the same period. Further physiological and genomic analysis found no apparent differences between the Atlantic V. coralliilyticus strains cultured here and pathogens from the Indo-Pacific but highlighted the diversity among strains and their immense genetic potential. In all, V. coralliilyticus may be causing coinfections that exacerbate existing SCTLD lesions, which could contribute to the intraspecific differences observed between colonies. This study describes potential coinfections contributing to SCTLD virulence as well as diagnostic tools capable of tracking the pathogen involved, which are important contributions to the management and understanding of SCTLD.

Complete genome sequence analysis of the Vibrio owensii strain SH-14 isolated from shrimp with acute hepatopancreatic necrosis disease

Vibrios are a group of very important bacterial pathogens in marine aquaculture industry and cause serious aquatic animal diseases, such as shrimp acute hepatopancreatic necrosis disease (AHPND). A new AHPND pathogen, the Vibrio owensii strain SH-14, was isolated from diseased shrimp in Shanghai, China. In this study, to better understand the pathogenesis of AHPND at the genomic level, the genome of the strain SH-14 was completely sequenced and analyzed. The SH-14 consists of two circular chromosomes of 3,689,702 bp and 2,430,445 bp, and of two plasmids named as pVHvo (69,148 bp) and pVHvo-R (78,918 bp), respectively. The pVHvo encodes the bi-toxic genes of pirAB, responsible for shrimp AHPND. The whole genomes contain a total of 5703 predicted open reading frames (ORFs), 129 tRNA genes and 37 rRNA genes. The average nucleotide identities (ANIs) between the SH-14 and the other V. owensii strains are all greater than 95%, confirming a new V. owensii strain of the SH-14. The taxonomic affiliation of the SH-14 is also supported by whole-genome alignment and nucleotide identity dotplot analyses. These results pave the way for further study of spread and epidemic of shrimp AHPND.

Ecology, histopathology, and microbial ecology of a white-band disease outbreak in the threatened staghorn coral Acropora cervicornis

This study is a multi-pronged description of a temperature-induced outbreak of white-band disease (WBD) that occurred in Acropora cervicornis off northern Miami Beach, Florida (USA), from July to October 2014. We describe the ecology of the disease and examine diseased corals using both histopathology and next-generation bacterial 16S gene sequencing, making it possible to better understand the effect this disease has on the coral holobiont, and to address some of the seeming contradictions among previous studies of WBD that employed either a purely histological or molecular approach. The outbreak began in July 2014, as sea surface temperatures reached 29°C, and peaked in mid-September, a month after the sea surface temperature maximum. The microscopic anatomy of apparently healthy portions of colonies displaying active disease signs appeared normal except for some tissue atrophy and dissociation of mesenterial filaments deep within the branch. Structural changes were more pronounced in visibly diseased fragments, with atrophy, necrosis, and lysing of surface and basal body wall and polyp structures at the tissue-loss margin. The only bacteria evident microscopically in both diseased and apparently healthy tissues with Giemsa staining was a Rickettsiales-like organism (RLO) occupying mucocytes. Sequencing also identified bacteria belonging to the order Rickettsiales in all fragments. When compared to apparently healthy fragments, diseased fragments had more diverse bacterial communities made up of many previously suggested potential primary pathogens and secondary (opportunistic) colonizers. Interactions between elevated seawater temperatures, the coral host, and pathogenic members of the diseased microbiome all contribute to the coral displaying signs of WBD.

Multiple Megaplasmids Confer Extremely High Levels of Metal Tolerance in Alteromonas Strains

Alteromonas is a widely distributed genus of marine Gammaproteobacteria, with representatives shown to be key players in diverse processes, including biogeochemical cycling and biofouling of marine substrata. While Alteromonas spp. are early colonizers of copper-based antifouling paints on marine vessels, their mechanism of tolerance is poorly understood. PacBio whole-genome sequencing of Alteromonas macleodii strains CUKW and KCC02, isolated from Cu/Ni alloy test coupons submerged in oligotrophic coastal waters, indicated the presence of multiple megaplasmids (ca. 200 kb) in both. A pulsed-field gel electrophoresis method was developed and used to confirm the presence of multiple megaplasmids in these two strains; it was then used to screen additional Alteromonas strains for which little to no sequencing data exist. Plasmids were not detected in any of the other strains. Bioinformatic analysis of the CUKW and KCC02 plasmids identified numerous genes associated with metal resistance. Copper resistance orthologs from both the Escherichia coli Cue and Cus and Pseudomonas syringae Cop systems were present, at times as multiple copies. Metal growth assays in the presence of copper, cobalt, manganese, and zinc performed with 10 Alteromonas strains demonstrated the ability of CUKW and KCC02 to grow at metal concentrations inhibitory to all the other strains tested. This study reports multiple megaplasmids in Alteromonas strains. Bioinformatic analysis of the CUKW and KCC02 plasmids indicate that they harbor elements of the Tra system conjugation apparatus, although their type of mobility remains to be experimentally verified.IMPORTANCE Copper is commonly used as an antifouling agent on ship hulls. Alteromonas spp. are early colonizers of copper-based antifouling paint, but their mechanism of tolerance is poorly understood. Sequencing of A. macleodii strains isolated from copper test materials for marine ships indicated the presence of multiple megaplasmids. Plasmids serve as key vectors in horizontal gene transfer and confer traits such as metal resistance, detoxification, ecological interaction, and antibiotic resistance. Bioinformatic analysis identified many metal resistance genes and genes associated with mobility. Understanding the molecular mechanisms and capacity for gene transfer within marine biofilms provides a platform for the development of novel antifouling solutions targeting genes involved in copper tolerance and biofilm formation.

Vibrio chemaguriensis sp. nov., from Sundarbans, Bay of Bengal

A new species of Vibrio (annotated as SBOTS_Iso1) was isolated in August 2014 from the Stn1 located in Chemaguri creek of Sundarbans mangrove ecoregion and taxonomically characterized using a polyphasic approach. Phenotypic analysis including biochemical tests and growth across a wide range of salinities indicated the typical estuarine characteristics of this new species. The bacterium was Gram negative, rod-shaped, oxidase and catalase negative and grows in the presence of NaCl. FAME analysis indicated 31.7% of the cellular fatty acids to be made up of 16:1 ω7c/16:1 ω6c. Amplification and sequencing of 16S rRNA and multilocus sequence analysis of four loci (2040 bp; rpoA, topA, mreB, pyrH) and additional sequence data of ftsZ, atpD, ompW and rpoB genes showed this isolate to be a member of Harveyi clade of the genus Vibrio. The closest phylogenetic neighbour was Vibrio alginolyticus ATCC 17749^T with 96.8% similarity. Whole-genome sequence data indicates the presence of ~ 5 Mbp genome. GGDC, orthoANIu and AAI indicated 45%, 92% and 0.962 identity respectively with genome of Vibrio alginolyticus ATCC 17749^T. The isolate SBOTS_Iso1 has been named Vibrio chemaguriensis sp. nov. on the name of the site from where it was first isolated.

Influence of Chemotaxis and Swimming Patterns on the Virulence of the Coral Pathogen Vibrio coralliilyticus

Chemotaxis, the directed movement toward or away from a chemical signal, can be essential to bacterial pathogens for locating hosts or avoiding hostile environments. The coral pathogen Vibrio coralliilyticus chemotaxes toward coral mucus; however, chemotaxis has not been experimentally demonstrated to be important for virulence. To further examine this, in-frame mutations were constructed in genes predicted to be important for V. coralliilyticus chemotaxis. Most Vibrio genomes contain multiple homologs of various chemotaxis-related genes, and two paralogs of each for cheB, cheR, and cheA were identified. Based on single mutant analyses, the paralogs cheB₂, cheR₂, and cheA₁ were essential for chemotaxis in laboratory assays. As predicted, the ΔcheA₁ and ΔcheR₂ strains had a smooth-swimming pattern, while the ΔcheB₂ strain displayed a zigzag pattern when observed under light microscopy. However, these mutants, unlike the parent strain, were unable to chemotax toward the known attractants coral mucus, dimethylsulfoniopropionate, and N-acetyl-d-glucosamine. The ΔcheB₂ strain and an aflagellate ΔfliG₁ strain were avirulent to coral, while the ΔcheA₁ and ΔcheR₂ strains were hypervirulent (90 to 100% infection within 14 h on average) compared to the wild-type strain (66% infection within 36 h on average). Additionally, the ΔcheA₁ and ΔcheR₂ strains appeared to better colonize coral fragments than the wild-type strain. These results suggest that although chemotaxis may be involved with infection (the ΔcheB₂ strain was avirulent), a smooth-swimming phenotype is important for bacterial colonization and infection. This study provides valuable insight into understanding V. coralliilyticus pathogenesis and how this pathogen may be transmitted between hosts.IMPORTANCE Corals are responsible for creating the immense structures that are essential to reef ecosystems; unfortunately, pathogens like the bacterium Vibrio coralliilyticus can cause fatal infections of reef-building coral species. However, compared to related human pathogens, the mechanisms by which V. coralliilyticus initiates infections and locates new coral hosts are poorly understood. This study investigated the effects of chemotaxis, the directional swimming in response to chemical signals, and bacterial swimming patterns on infection of the coral Montipora capitata Infection experiments with different mutant strains suggested that a smooth-swimming pattern resulted in hypervirulence. These results demonstrate that the role of chemotaxis in coral infection may not be as straightforward as previously hypothesized and provide valuable insight into V. coralliilyticus pathogenesis.

Sponge chemical defenses are a possible mechanism for increasing sponge abundance on reefs in Zanzibar

Coral reefs are experiencing increasing anthropogenic impacts that result in substantial declines of reef-building corals and a change of community structure towards other benthic invertebrates or macroalgae. Reefs around Zanzibar are exposed to untreated sewage and runoff from the main city Stonetown. At many of these sites, sponge cover has increased over the last years. Sponges are one of the top spatial competitors on reefs worldwide. Their success is, in part, dependent on their strong chemical defenses against predators, microbial attacks and other sessile benthic competitors. This is the first study that investigates the bioactive properties of sponge species in the Western Indian Ocean region. Crude extracts of the ten most dominant sponge species were assessed for their chemical defenses against 35 bacterial strains (nine known as marine pathogens) using disc diffusion assays and general cytotoxic activities were assessed with brine shrimp lethality assays. The three chemically most active sponge species were additionally tested for their allelopathic properties against the scleractinian coral competitor Porites sp.. The antimicrobial assays revealed that all tested sponge extracts had strong antimicrobial properties and that the majority (80%) of the tested sponges were equally defended against pathogenic and environmental bacterial strains. Additionally, seven out of ten sponge species exhibited cytotoxic activities in the brine shrimp assay. Moreover, we could also show that the three most bioactive sponge species were able to decrease the photosynthetic performance of the coral symbionts and thus were likely to impair the coral physiology.

Vibrio alginolyticus 16S-23S intergenic spacer region analysis, and PCR assay for identification of coral pathogenic strain XSBZ03

Porites andrewsi white syndrome (PAWS), caused by Vibrio alginolyticus strains XSBZ03 and XSBZ14, poses a serious threat to corals in the South China Sea. To obtain a specific target against which to develop a rapid PCR detection method for the coral pathogenic strain XSBZ03, the 16S-23S rRNA gene intergenic spacer (IGS) region of 4 strains of V. alginolyticus, including the XSBZ03 and XSBZ14 strains, was amplified, sequenced and analyzed. Six types of IGS were found: IGS0, IGSG, IGSIA, IGSAG, IGSGLV, and IGSGLAV. IGS0, IGSG, IGSIA, IGSAG and IGSGLV appeared to be the most prevalent forms in the 4 strains and the percentage identity range within each type was 91.4-100%, 89.3-98.5%, 83.0-99.8%, 91.5-95.6%, and 88.7-99.3%, respectively. IGSGLAV was found only in the HN08155 strain, a causative agent of fish disease. IGSGLAV, IGSGLV and IGSAG are reported here for the first time in V. alginolyticus. An IGS sequence specific to the XSBZ03 strain was identified following alignment of the homologous IGSs, and used to design strain-specific primers for its rapid identification by PCR. The results from PCR analysis suggest that the method is a rapid, practical, and reliable tool for the identification of the XSBZ03 strain in samples of isolated bacteria, as well as seawater and coral samples spiked with the bacterial strain. This is the first report of a rapid diagnostic assay for a causative agent of PAWS, based on PCR detection of a coral pathogen at the strain level. After applying this assay in coral transplantation, the survival rates of transplanted corals were significantly increased. This diagnostic assay should aid with both the elucidation of the cause of the disease, and transplantation of PAWS-free P. andrewsi in the South China Sea.

Factors affecting infection of corals and larval oysters by Vibrio coralliilyticus

The bacterium Vibrio coralliilyticus can threaten vital reef ecosystems by causing disease in a variety of coral genera, and, for some strains, increases in virulence at elevated water temperatures. In addition, strains of V. coralliilyticus (formally identified as V. tubiashii) have been implicated in mass mortalities of shellfish larvae causing significant economic losses to the shellfish industry. Recently, strain BAA-450, a coral pathogen, was demonstrated to be virulent towards larval Pacific oysters (Crassostrea gigas). However, it is unclear whether other coral-associated V. coralliilyticus strains can cause shellfish mortalities and if infections are influenced by temperature. This study compared dose dependence, temperature impact, and gross pathology of four V. coralliilyticus strains (BAA-450, OCN008, OCN014 and RE98) on larval C. gigas raised at 23°C and 27°C, and evaluated whether select virulence factors are required for shellfish infections as they are for corals. All strains were infectious to larval oysters in a dose-dependent manner with OCN014 being the most pathogenic and BAA-450 being the least. At 27°C, higher larval mortalities (p < 0.05) were observed for all V. coralliilyticus strains, ranging from 38.8−93.7%. Gross pathological changes to the velum and cilia occurred in diseased larvae, but there were no distinguishable differences between oysters exposed to different V. coralliilyticus strains or temperatures. Additionally, in OCN008, the predicted transcriptional regulator ToxR and the outer membrane protein OmpU were important for coral and oyster disease, while mannose sensitive hemagglutinin type IV pili were required only for coral infection. This study demonstrated that multiple coral pathogens can infect oyster larvae in a temperature-dependent manner and identified virulence factors required for infection of both hosts.

AHL-lactonase expression in three marine emerging pathogenic Vibrio spp. reduces virulence and mortality in brine shrimp (Artemia salina) and Manila clam (Venerupis philippinarum)

Bacterial infectious diseases produced by Vibrio are the main cause of economic losses in aquaculture. During recent years it has been shown that the expression of virulence genes in some Vibrio species is controlled by a population-density dependent gene-expression mechanism known as quorum sensing (QS), which is mediated by the diffusion of signal molecules such as N-acylhomoserine lactones (AHLs). QS disruption, especially the enzymatic degradation of signalling molecules, known as quorum quenching (QQ), is one of the novel therapeutic strategies for the treatment of bacterial infections. In this study, we present the detection of AHLs in 34 marine Vibrionaceae strains. Three aquaculture-related pathogenic Vibrio strains, V. mediterranei VibC-Oc-097, V. owensii VibC-Oc-106 and V. coralliilyticus VibC-Oc-193 were selected for further studies based on their virulence and high production of AHLs. This is the first report where the signal molecules have been characterized in these emerging marine pathogens and correlated to the expression of virulence factors. Moreover, the results of AHL inactivation in the three selected strains have been confirmed in vivo against brine shrimps (Artemia salina) and Manila clams (Venerupis philippinarum). This research contributes to the development of future therapies based on AHL disruption, the most promising alternatives for fighting infectious diseases in aquaculture.

The high prevalence of pathogenic Vibrio harveyi with multiple antibiotic resistance in scale drop and muscle necrosis disease of the hybrid grouper, Epinephelus fuscoguttatus (♀) × E. lanceolatus (♂), in China

Scale drop and muscle necrosis disease with high mortality widely occurred recently in the hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂), a crucial cultured marine fish species in China. In this study, 30 Harveyi clade isolates of 27 Vibrio harveyi strains were isolated from diseased hybrid groupers in the south-east and north-east coastal areas of China. A total of 22 V. harveyi strains were determined to be pathogenic, and most challenged fish died within 2 days of infection; surviving individuals exhibited scale drop and deep dermal lesions as naturally diseased fish. Although five typical virulence genes, including luxR, toxR_Vh , chiA, serine protease and vhh widely existed in V. harveyi, no obvious correlation was established between virulent strains and virulence genes harboured in them. Furthermore, multiple antibiotic resistance was widely exhibited in Harveyi clade strains, particularly for penicillins, polypeptides, lincomycins, acetylspiramycin, streptomycin, metronidazole and bacitracin. And the multiple antibiotic resistance indices were gradually decreased from southern to northern areas of China. This study demonstrated that the pathogenic V. harveyi with multiple antibiotic resistance is highly prevalent in hybrid grouper in China, which requires particular attention.

Influence of salinity and sedimentation on Vibrio infection of the Hawaiian coral Montipora capitata

Environmental cofactors alter host-pathogen interactions and influence disease dynamics by impairing host resistance and/or increasing pathogen virulence. Terrestrial runoff is recognized as a major threat to coral reef health. However, the direct links between runoff and coral disease are not clear. Montipora white syndrome (MWS) is a coral disease that occurs in the Hawaiian archipelago, can be caused by various bacterial pathogens, including Vibrio species, and is linked to conditions associated with heavy rainfall and runoff. The objective of this study was to determine whether a short-term hyposalinity stress (20 ppt for 24 h) or sedimentation stress (1000 g m-2 d-1) would influence bacterial infection of the coral Montipora capitata. Hyposalinity increased M. capitata susceptibility to infection by 2 MWS pathogens, Vibrio coralliilyticus strain OCN008 and Vibrio owensii strain OCN002. Specifically, hyposalinity allowed OCN008 to infect at lower doses (106 CFU ml-1 compared with 108 CFU ml-1) and reduced the amount of time before onset of OCN002 infection at high doses (108 CFU ml-1). In contrast, short-term sedimentation stress did not affect M. capitata infection by either of these 2 pathogens. Although several studies have found a correlation between runoff and increased coral disease prevalence in field studies, this is the first study to show that one aspect of runoff (reduced salinity) enhances bacterial infection of coral using manipulative experiments.

Abundance and Multilocus Sequence Analysis of Vibrio Bacteria Associated with Diseased Elkhorn Coral (Acropora palmata) of the Florida Keys

The critically endangered elkhorn coral (Acropora palmata) is affected by white pox disease (WPX) throughout the Florida Reef Tract and wider Caribbean. The bacterium Serratia marcescens was previously identified as one etiologic agent of WPX but is no longer consistently detected in contemporary outbreaks. It is now believed that multiple etiologic agents cause WPX; however, to date, no other potential pathogens have been thoroughly investigated. This study examined the association of Vibrio bacteria with WPX occurrence from August 2012 to 2014 at Looe Key Reef in the Florida Keys, USA. The concentration of cultivable Vibrio was consistently greater in WPX samples than in healthy samples. The abundance of Vibrio bacteria relative to total bacteria was four times higher in samples from WPX lesions than in adjacent apparently healthy regions of diseased corals based on quantitative PCR (qPCR). Multilocus sequence analysis (MLSA) was used to assess the diversity of 69 Vibrio isolates collected from diseased and apparently healthy A. palmata colonies and the surrounding seawater. Vibrio species with known pathogenicity to corals were detected in both apparently healthy and diseased samples. While the causative agent(s) of contemporary WPX outbreaks remains elusive, our results suggest that Vibrio spp. may be part of a nonspecific heterotrophic bacterial bloom rather than acting as primary pathogens. This study highlights the need for highly resolved temporal sampling in situ to further elucidate the role of Vibrio during WPX onset and progression.IMPORTANCE Coral diseases are increasing worldwide and are now considered a major contributor to coral reef decline. In particular, the Caribbean has been noted as a coral disease hot spot, owing to the dramatic loss of framework-building acroporid corals due to tissue loss diseases. The pathogenesis of contemporary white pox disease (WPX) outbreaks in Acropora palmata remains poorly understood. This study investigates the association of Vibrio bacteria with WPX.

Pseudoalteromonas piratica strain OCN003 is a coral pathogen that causes a switch from chronic to acute Montipora white syndrome in Montipora capitata

Reports of mass coral mortality from disease have increased over the last two decades. Montipora white syndrome (MWS) is a tissue loss disease that has negatively impacted populations of the coral Montipora capitata in Kāne'ohe Bay, Hawai'i. Two types of MWS have been documented; a progressive disease termed chronic MWS (cMWS), that can be caused by Vibrio owensii strain OCN002, and a comparatively faster disease termed acute MWS (aMWS), that can be caused by Vibrio coralliilyticus strain OCN008. M. capitata colonies exhibiting cMWS can spontaneously switch to aMWS in the field. In this study, a novel Pseudoalteromonas species, P. piratica strain OCN003, fulfilled Koch's postulates of disease causation as another etiological agent of aMWS. Additionally, OCN003 induced a switch from cMWS to aMWS on M. capitata in laboratory infection trials. A comparison of OCN003 and Vibrio coralliilyticus strain OCN008, showed that OCN003 was more effective at inducing the cMWS to aMWS switch in M. capitata than OCN008. This study is the first to demonstrate that similar disease signs on one coral species (aMWS on M. capitata) can be caused by multiple pathogens, and describes the first Pseudoalteromonas species that infects coral.

Intra-colony disease progression induces fragmentation of coral fluorescent pigments

As disease spreads through living coral, it can induce changes in the distribution of coral's naturally fluorescent pigments, making fluorescence a potentially powerful non-invasive intrinsic marker of coral disease. Here, we show the usefulness of live-imaging laser scanning confocal microscopy to investigate coral health state. We demonstrate that the Hawaiian coral Montipora capitata consistently emits cyan and red fluorescence across a depth gradient in reef habitats, but the micro-scale spatial distribution of those pigments differ between healthy coral and coral affected by a tissue loss disease. Naturally diseased and laboratory infected coral systematically exhibited fragmented fluorescent pigments adjacent to the disease front as indicated by several measures of landscape structure (e.g., number of patches) relative to healthy coral. Histology results supported these findings. Pigment fragmentation indicates a disruption in coral tissue that likely impedes translocation of energy within a colony. The area of fragmented fluorescent pigments in diseased coral extended 3.03 mm ± 1.80 mm adjacent to the disease front, indicating pathogenesis was highly localized rather than systemic. Our study demonstrates that coral fluorescence can be used as a proxy for coral health state, and, such patterns may help refine hypotheses about modes of pathogenesis.

Intraspecific differences in molecular stress responses and coral pathobiome contribute to mortality under bacterial challenge in Acropora millepora

Disease causes significant coral mortality worldwide; however, factors responsible for intraspecific variation in disease resistance remain unclear. We exposed fragments of eight Acropora millepora colonies (genotypes) to putatively pathogenic bacteria (Vibrio spp.). Genotypes varied from zero to >90% mortality, with bacterial challenge increasing average mortality rates 4–6 fold and shifting the microbiome in favor of stress-associated taxa. Constitutive immunity and subsequent immune and transcriptomic responses to the challenge were more prominent in high-mortality individuals, whereas low-mortality corals remained largely unaffected and maintained expression signatures of a healthier condition (i.e., did not launch a large stress response). Our results suggest that lesions appeared due to changes in the coral pathobiome (multiple bacterial species associated with disease) and general health deterioration after the biotic disturbance, rather than the direct activity of any specific pathogen. If diseases in nature arise because of weaknesses in holobiont physiology, instead of the virulence of any single etiological agent, environmental stressors compromising coral condition might play a larger role in disease outbreaks than is currently thought. To facilitate the diagnosis of compromised individuals, we developed and independently cross-validated a biomarker assay to predict mortality based on genes whose expression in asymptomatic individuals coincides with mortality rates.

Conditional persistence and tolerance characterize endoparasite-colonial host interactions

Colonial hosts offer unique opportunities for exploitation by endoparasites resulting from extensive clonal propagation, but these interactions are poorly understood. The freshwater bryozoan, Fredericella sultana, and the myxozoan, Tetracapsuloides bryosalmonae, present an appropriate model system for examining such interactions. F. sultana propagates mainly asexually, through colony fragmentation and dormant propagules (statoblasts). Our study examines how T. bryosalmonae exploits the multiple transmission routes offered by the propagation of F. sultana, evaluates the effects of such transmission on its bryozoan host, and tests the hypothesis that poor host condition provokes T. bryosalmonae to bail out of a resource that may soon be unsustainable, demonstrating terminal investment. We show that infections are present in substantial proportions of colony fragments and statoblasts over space and time and that moderate infection levels promote statoblast hatching and hence effective fecundity. We also found evidence for terminal investment, with host starvation inducing the development of transmission stages. Our results contribute to a growing picture that interactions of T. bryosalmonae and F. sultana are generally characterized by parasite persistence, facilitated by multiple transmission pathways and host condition-dependent developmental cycling, and host tolerance, promoted by effective fecundity effects and an inherent capacity for renewed growth and clonal replication.

Assessment of disease lesion removal as a method to control chronic Montipora white syndrome

Coral colonies in Kāne'ohe Bay, Hawai'i (USA), are afflicted with the tissue loss disease chronic Montipora white syndrome (cMWS). Here we show that removal of chronic disease lesions is a potential method to slow the progression of cMWS in M. capitata. Over the 24 wk observation period, treatment colonies lost almost half the amount of tissue that was lost by control colonies. The percentage of tissue loss at each sampling interval (mean ± SEM; treatment: 1.17 ± 0.47%, control: 2.25 ± 0.63%) and the rate of tissue loss per day (treatment: 0.13 ± 0.04%, control: 0.27 ± 0.08%) were both significantly lower on treated colonies than control colonies. While lesion removal stopped tissue loss at the initial infection site, which allowed colony healing, it did not prevent re-infection; in all but one of the treated colonies, new cMWS lesions appeared in other areas of the colony but not around the treatment margins. Additionally, the rate of new infections was similar between treatment and control colonies, indicating that physical injury from lesion removal did not appear to increase cMWS susceptibility. These results indicate that lesion removal reduced morbidity in M. capitata exhibiting cMWS but did not stop the disease.