Vibrio shiloi

  • Coral pathogen

Overview

Vibrio shiloi is a Gram-negative marine bacterium recognized as a major coral pathogen, particularly affecting the Mediterranean coral Oculina patagonica. This temperature-dependent pathogen causes coral bleaching by adhering to coral mucus, penetrating tissues, and producing toxins that inhibit zooxanthellae photosynthesis. V. shiloi represents one of the best-studied examples of bacterial coral disease and serves as a model system for understanding coral-pathogen interactions in marine aquarium systems.

Affected species (hosts)

Primary Coral Hosts:

  • Oculina patagonica – primary host, severe bleaching susceptibility
  • Other zooxanthellate corals – various species affected
  • Zooxanthellae symbionts – directly targeted by bacterial toxins

Secondary Marine Hosts:

  • Aiptasia pallida (sea anemone) – tissue necrosis, model organism
  • Hermodice carunculata (fireworm) – acts as reservoir and vector

Aquarium Relevance:

  • Mediterranean coral species in specialized aquarium systems
  • Model anemones like Aiptasia commonly kept by hobbyists
  • Temperature-sensitive pathogen relevant to reef tank management

Temperature Dependence and Pathogenesis Mechanisms

Temperature-Dependent Virulence. V. shiloi exhibits strong temperature dependence, with pathogenicity occurring primarily at temperatures between 20-32°C. Virulence factors including extracellular superoxide dismutase (SOD) and adhesins are upregulated at higher temperatures, making this pathogen particularly relevant during summer months or in warm aquarium conditions.

Adhesion and Tissue Penetration. The bacterium adheres specifically to coral mucus through receptors produced by zooxanthellae, explaining why only zooxanthellate corals are susceptible. Following adhesion, V. shiloi penetrates coral tissues and multiplies intracellularly, eventually producing toxins that disrupt the coral-algae symbiosis.

Toxin Production and Bleaching. V. shiloi produces several virulence factors including toxin P, a proline-rich peptide that directly inhibits photosynthesis in zooxanthellae. The bacterium also secretes factors that bleach and lyse zooxanthellae, leading to the characteristic coral bleaching syndrome.

Viable-But-Not-Culturable (VBNC) State. During cooler months, V. shiloi enters a VBNC state where it remains alive but non-culturable. Coral defense mechanisms can kill intracellular bacteria at low temperatures, requiring new infections each spring when temperatures rise.

Vector-Mediated Transmission. The fireworm Hermodice carunculata serves as a winter reservoir and spring-summer vector for V. shiloi, facilitating transmission between coral colonies and potentially introducing the pathogen to aquarium systems through live rock or coral imports.

Management and Prevention Strategies

Prevention. Implement strict quarantine protocols for new coral additions, particularly Mediterranean species or corals from areas with known V. shiloi presence. Monitor water quality parameters and maintain stable environmental conditions.

Temperature Management. Monitor and control water temperatures carefully, as V. shiloi virulence increases significantly with elevated temperatures. Avoid temperature stress during coral acclimation and maintain consistent thermal conditions.

Early Detection. Watch for characteristic bleaching patterns, particularly in Oculina species or related corals. Look for signs of tissue necrosis in anemones, which may indicate V. shiloi infection.

Biological Control. Research suggests that native coral commensal bacteria can inhibit V. shiloi, especially at lower temperatures. Maintaining healthy coral microbiomes through probiotic approaches may provide natural protection.

Vector Control. Be cautious with fireworms (Hermodice carunculata) which can serve as reservoirs and vectors. Quarantine any live rock or coral imports that may harbor these worms.

Antibiotic Considerations: While no specific antibiotics are established for V. shiloi treatment, focus on prevention and environmental management. The coral probiotic hypothesis suggests that maintaining beneficial bacterial communities may be more effective than antimicrobial approaches.

V. shiloi in reef tanks

Prevalence

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Looking at how common this pathogen is in other tanks can help you gauge whether finding it in your tank is expected or unusual.

Abundance Distribution

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Comparing the levels of this pathogen in your tank with those found in other tanks provides a context for interpreting your test results.

References

Rosenberg, E., & Falkovitz, L. (2004). The Vibrio shiloi/Oculina patagonica model system of coral bleaching. Annual Review of Microbiology, 58, 143-159. https://doi.org/10.1146/annurev.micro.58.030603.123610

Kushmaro, A., et al. (2001). Vibrio shiloi sp. nov., the causative agent of bleaching of the coral Oculina patagonica. International Journal of Systematic and Evolutionary Microbiology, 51(4), 1383-1388. https://doi.org/10.1099/00207713-51-4-1383

Banin, E., et al. (2000). Penetration of the coral-bleaching bacterium Vibrio shiloi into Oculina patagonica. Applied and Environmental Microbiology, 66(7), 3031-3036. https://doi.org/10.1128/aem.66.7.3031-3036.2000

Ben-Haim, Y., et al. (1999). Inhibition of photosynthesis and bleaching of zooxanthellae by the coral pathogen Vibrio shiloi. Environmental Microbiology, 1(3), 223-229. https://doi.org/10.1046/j.1462-2920.1999.00027.x

Sussman, M., et al. (2003). The marine fireworm Hermodice carunculata is a winter reservoir and spring-summer vector for the coral-bleaching pathogen Vibrio shiloi. Environmental Microbiology, 5(4), 250-255. https://doi.org/10.1046/j.1462-2920.2003.00424.x

Banin, E., et al. (2003). Superoxide dismutase is a virulence factor produced by the coral bleaching pathogen Vibrio shiloi. Current Microbiology, 46(6), 418-422. https://doi.org/10.1007/s00284-002-3912-5

Frydenborg, B., et al. (2014). Temperature-dependent inhibition of opportunistic Vibrio pathogens by native coral commensal bacteria. Microbial Ecology, 67(2), 392-401. https://doi.org/10.1007/s00248-013-0334-9

Zaragoza, W., et al. (2014). Outcomes of infections of sea anemone Aiptasia pallida with Vibrio spp. pathogenic to corals. Microbial Ecology, 68(2), 388-396. https://doi.org/10.1007/s00248-014-0397-2

Reshef, L., et al. (2006). The coral probiotic hypothesis. Environmental Microbiology, 8(12), 2068-2073. https://doi.org/10.1111/j.1462-2920.2006.01148.x

Banin, E., et al. (2001). Proline-rich peptide from the coral pathogen Vibrio shiloi that inhibits photosynthesis of zooxanthellae. Applied and Environmental Microbiology, 67(4), 1536-1541. https://doi.org/10.1128/aem.67.4.1536-1541.2001