Vibrio harveyi is a Gram-negative, bioluminescent, marine bacterium in the genus Vibrio that was first discovered by Johnson and Shunk in their 1963 publication "An interesting new species of luminous bacteria". V. harveyi is rod-shaped, motile (via polar flagella), facultatively anaerobic, halophilic, and competent for both fermentative and respiratory metabolism. It is typically found in aquatic ecosystems — particularly in warmer tropical waters (optimum growth: 30° to 35 °C) — as a free-living bacterium. However, V. harveyi can also live commensally with other marine life, form biofilms on marine surfaces, and act as a pathogen in organisms like coral and oysters. This bacterium is tolerant to fluxes in environmental conditions, a characteristic attributed to its rapid adaptation caused by mutations and Horizontal Gene Transfer. This tolerance allows V. harveyi to thrive in environments affected by climate change.

Certain strains of V. harveyi can cause disease in marine life, such as luminous vibriosis — a disease that causes commercially farmed penaeid prawns to glow in the dark. The pathogenicity of these strains can be enhanced in environments affected by climate change, primarily due to the weakening of marine hosts. Despite its harmful effects, V. harveyi plays a beneficial role in nutrient cycling by using chitin — a building block of marine invertebrate exoskeletons — as a carbon source. It does so by breaking chitin down into simpler molecules that are used and eventually returned to the aquatic system to be taken up by other organisms. This species is also thought to be the cause of the milky seas effect, in which, a uniform blue glow is emitted from seawater during the night. Some glows can cover nearly 6,000 sq mi (16,000 km²). It also belongs to the Harveyi clade alongside Vibrio campbellii, Vibrio natriegens, Vibrio alginolyticus, and Vibrio parahaemolyticus.

thumb|Phylogenetic tree of the genus [[Vibrio]]

Relations to other Vibrio species

Although closely related to V. campbellii — with a DNA similarity of 61% to 74% — V. harveyi has also been found to contain similar genes to other bacteria outside its clade such as Vibrio cholerae, specifically thought to have occurred through Horizontal Gene Transfer. This was hypothesized after ToxR, a regulator for the cholera toxin gene, was found to exist within all Vibrio species within the Harveyi clade.

Plasmid use

thumb|Structure of Plasmids as Circular DNA, separate from the Bacteria's DNA

These plasmids act as storage for important genes V. harveyi can use to increase its pathogenicity, antibiotic-resistance, and adaptation. They also play a major role in Horizontal Gene Transfer, meaning that individuals of a strain are able to transfer genes and gain genes from individuals of another strain, by a process called conjugation. This exchange of traits from other bacteria allows V. harveyi to adapt rapidly as it does not have to solely wait for evolution or mutation to gain access to new traits like many other species..

Adherence

Strains of V. harveyi have been documented to have different pili genes such as, mshB and pilA. Research has suggested that some V. harveyi infections in fish may be the result of an initial C. irritans infection, although the exact nature of the relationship between the two organisms is unclear Despite its relatedness to A. fischeri, V. harveyi lacks a LuxI/R quorum-sensing system, and instead employs a hybrid quorum-sensing circuit, detecting its AI through a membrane-bound histidine kinase and using a phosphorelay to convert information about the population size to changes in gene expression. Since their identification in V. harveyi, such hybrid systems have been identified in many other bacterial species. Qrr RNA molecules are responsible for controlling regulator translation, repressing and promoting factors dependent on cell density. V. harveyi uses a second AI, termed autoinducer-2 or AI-2, which is unusual because it is made and detected by a variety of different bacteria, both Gram-negative and Gram-positive. Thus, V. harveyi has been instrumental to the understanding and appreciation of interspecies bacterial communication.

Previous research has characterized this quorum sensing (QS) system in V. harveyi as a "parallel circuit" due the system's architecture where multiple chemical signals are integrated to coordinate the production of bioluminescence.

The three-channel sensory architecture

V. harveyi utilizes three distinct autoinducers (AIs) and three cognate membrane-bound receptors, all functioning in parallel, in order to channel information into a singular shared regulatory pathway:

System 1 (Intraspecies)

This system uses HAI-1 (Harveyi-Autoinducer 1), an acyl-homoserine lactone (AHL) produced by LuxM and detected by LuxN. This signal enables communication between V. harveyi members.

System 3 (Intrageneric)

This system uses CAI-1 (Cholerae-Autoinducer 1), produced by CqsA and detected by the CqsS sensor. This signal is shared among members of the Vibrio genus, thus enabling them to monitor the composition of the surrounding community.

For instance, the luciferase enzyme was found to be the responsible catalyst for bioluminescence. Light is only produced in V. harveyi when a reduced flavin mononucleotide (FMNH2) and long-chain aliphatic aldehyde are oxidized in the presence of O2. This oxidation reaction in turn releases energy as blue-green light, with a peak emission near 490 nm.

Habitat preference & environmental conditions

V. harveyi has been shown to exhibit distinct spatial & temporal dynamics, primarily driven by factors such as water temperature, salinity, and depth.

Temperature & pH

V. harveyi bacteria seem to exhibit a robust capacity for adaptation across a diverse range of environmental conditions. White Syndrome includes multiple diseases such as 'White Band', 'White Plague', and 'Shut Down Reaction'.

Prevention and control

Given the widespread impacts of V. harveyi on marine and aquaculture organisms, several control alternatives have been explored.

Vaccines

Various vaccines have been developed and largely marketed to control the shrimp and fish disease associated with V. harveyi. This includes whole-cell vaccines in which injection into barramundi fish (Lates calcarifer) has succeeded in making this species produce antibodies. Lastly, a DNA vaccine also has been developed and results in a wider range of RPSs.

References

  • V. harveyi at NCBI
  • Vibrios at NCBI
  • Type strain of Vibrio harveyi at BacDive - the Bacterial Diversity Metadatabase