Photobacterium
Encyclopedia
Photobacterium is a genus of gram-negative
bacteria
in the family Vibrionaceae
. Members of the genus are bioluminescent, that is they have the ability to emit light
.
Many species, including Photobacterium leiognathi and Photobacterium phosphoreum
, live in symbiosis
with marine organisms.
Species such as Photobacterium profundum
are adapted for optimal growth in the deep cold seas making it both a psychrophile
(an
(an organism which thrives at high pressures).
s which is proportional to cell density and therefore free-living photobacterium will not fluoresce. Their association with fish may be: symbiotic growth within fish for the formation of light organs
, as a neutral entity on the surface or within the intestines of fish, as decomposers of dead fish, or as an agent of disease.
of the Deep Sea Tanner Crab (Chionoecetes tanneri). The species Photobacterium damselae are among the most virulent and are divided into two subspecies: piscicida and damsela. P. damselae subspecies piscicida is the causative agent of fish pasteurellosis
. Bacterial colonies grow on the infected fish's spleen and kidney, eventually leading to mortality. This disease accounts for severe losses in some fish farming enterprises with some of the most susceptible fish including Yellowfin tuna (Thunnus albacares)
, certain Seabreams (Sparus spp.), Striped bass (Morone saxatilis)
, and White perch (Morone americana)
. This subspecies is not pathogenic for humans.
, eels (Anguilla anguilla), brown sharks (Carcharhinus plumbeus), Yellowtails (Seriiola quinqueradiata), seabreams (Sparus spp.) and turbots (Scophthalmus spp.)
. This subspecies has been shown to be pathogenic for humans as it has been isolated from human wounds and has been shown to cause primary septicimia in healthy humans.
tion of the gills and liver along with the characteristic accumulation of mucus around the gills. It has been noted that the infected fish will swim violently a few minutes before death occurs
outbreaks gained from an increase in ulcers noted among the fish populations seem to correlate to warmer seasons, suggesting a seasonal distribution in the incidence of the disease, dependant upon the waters temperature and salinity along with a decreased resistance caused by physiological changes experienced by the host during sexual maturity.
Seawater is the most likely mode of transmission of the virulent cells of the pathogen. Once it comes into contact with the outer surface of the fish, it is able to adhere to skin and resist the bactericidal action of the skin mucus layer
, thus suggesting that the skin is the site of entry into the host. This bacterium could therefore represent a significant threat to aquacultured fish species, especially those living in crowded and stressed conditions, where the spread of the disease could be accelerated through direct contact and thus pose a threat to humans.
Gram-negative
Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...
bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
in the family Vibrionaceae
Vibrionaceae
The Vibrionaceae are a family of Proteobacteria, given their own order. Inhabitants of fresh or salt water, several species are pathogenic, including the type species Vibrio cholerae, which is the agent responsible for cholera...
. Members of the genus are bioluminescent, that is they have the ability to emit light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
.
Many species, including Photobacterium leiognathi and Photobacterium phosphoreum
Photobacterium phosphoreum
Photobacterium phosphoreum or Vibrio phosphoreum is a Gram-negative bioluminescent bacterium living in symbiosis with marine organisms. It can emit bluish-green light thanks to a chemical reaction between FMN, luciferin and molecular oxygen catalysed by an enzyme called Luciferase.- In Popular...
, live in symbiosis
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
with marine organisms.
Species such as Photobacterium profundum
Photobacterium profundum
Photobacterium profundum is a deep sea Gammaproteobacterium, belonging to the family Vibrionaceae and genus Photobacterium. Like other members of this genus, P. profundum is a marine organism and has two circular chromosomes. P...
are adapted for optimal growth in the deep cold seas making it both a psychrophile
Psychrophile
Psychrophiles or cryophiles are extremophilic organisms that are capable of growth and reproduction in cold temperatures, ranging from −15°C to +10°C. Temperatures as low as −15°C are found in pockets of very salty water surrounded by sea ice. They can be contrasted with thermophiles, which...
(an
Piezophile
A piezophile is an organism which thrives at high pressures, such as deep sea bacteria or archaea. They are generally found on ocean floors, where pressure often exceeds 380 atm . Some have been found at the bottom of the Pacific Ocean where the maximum pressure is roughly 117 MPa...
(an organism which thrives at high pressures).
Taxonomy
There are currently 15 species with numerous subspecies known within the genus Photobacterium. The development of 16S RNA sequencing has led to many species being shifted into and out of this genus. Photobacterium can be distinguished from other genera based on identifiable characteristics.Identifying characteristics
- Morphological shapes are straight or plump rods
- Cell wall structure is classified as gram-negative
- Require sodium for growth
- Contain 1-3 polar flagellaFlagellumA flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...
- Are luminescent
- Incapable of forming resistant endospores
- Are chemoorganotrophChemoorganotrophChemoorganotrophs are organisms which use organic compounds as their energy source. These organic chemicals include glucose and acetate. All animals are chemoorganotrophs, as are fungi, protozoa, and some bacteria. Indeed, most heterotrophs are chemoorganotrophs. However, chemolithotrophs instead...
s
Ecology
Photobacterium are primarily marine organisms (hence the use of sodium for growth). They may be free-living or found as colonies associated with certain species of fish. These organisms do not contain any pigmentation and therefore will appear white or colorless. When there is a high density of cells forming a colony, they will exhibit fluorescence. However, the fluorescence is based on the accumulation of autoinducerAutoinducer
Autoinducers are chemical signaling molecules that are produced and used by bacteria participating in quorum sensing. Quorum sensing is a phenomenon that allows both Gram-negative and Gram-positive bacteria to sense one another and to regulate a wide variety of physiological activities. Such...
s which is proportional to cell density and therefore free-living photobacterium will not fluoresce. Their association with fish may be: symbiotic growth within fish for the formation of light organs
Bioluminescence
Bioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...
, as a neutral entity on the surface or within the intestines of fish, as decomposers of dead fish, or as an agent of disease.
Pathogenicity
Some of the 15 known species of Photobacterium have evolved into pathogens of marine life. Some of these diseases affect commercially important fish and can therefore indirectly impact human health through their consumption. This genus has been shown to degrade the chitinChitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
of the Deep Sea Tanner Crab (Chionoecetes tanneri). The species Photobacterium damselae are among the most virulent and are divided into two subspecies: piscicida and damsela. P. damselae subspecies piscicida is the causative agent of fish pasteurellosis
Pasteurellosis
Pasteurellosis is an infection with a species of the bacteria genus Pasteurella, which is found in humans and animals.Pasteurella multocida is carried in mouth and respiratory tract of several animals, notably cats. It is a small Gram negative bacillus with bipolar staining by Wayson stain...
. Bacterial colonies grow on the infected fish's spleen and kidney, eventually leading to mortality. This disease accounts for severe losses in some fish farming enterprises with some of the most susceptible fish including Yellowfin tuna (Thunnus albacares)
Yellowfin tuna
The yellowfin tuna is a species of tuna found in pelagic waters of tropical and subtropical oceans worldwide.Yellowfin is often marketed as ahi, from its Hawaiian name ahi although the name ahi in Hawaiian also refers to the closely related bigeye tuna. The species name, albacares can lead to...
, certain Seabreams (Sparus spp.), Striped bass (Morone saxatilis)
Striped bass
The striped bass is the state fish of Maryland, Rhode Island, South Carolina, and the state saltwater fish of New York, Virginia, and New Hampshire...
, and White perch (Morone americana)
White perch
The white perch, Morone americana, is not a true perch but is, rather, a fish of the temperate bass family, Moronidae, notable as a food and game fish in eastern North America.The name "white perch" is sometimes erroneously applied to the white crappie....
. This subspecies is not pathogenic for humans.
Photobacterium damselae subspecies damsela
Fish-virulent strains of this subspecies of P. damselae cause septicemia in species of fish such as; damselfish (Family Pomacentridae)Damselfish
Damselfish comprise the family Pomacentridae except those of the genera Amphiprion and Premnas. They can grow up to long. While most are marine, a few species inhabit the lower stretches of rivers in freshwater. Damselfish usually have bright colors. in tropical coral reefs, and many of those are...
, eels (Anguilla anguilla), brown sharks (Carcharhinus plumbeus), Yellowtails (Seriiola quinqueradiata), seabreams (Sparus spp.) and turbots (Scophthalmus spp.)
Turbot
The turbot is a species of flatfish in the family Scophthalmidae. It is native to marine or brackish waters of the North Atlantic, Baltic Sea and the Mediterranean Sea.-Etymology:...
. This subspecies has been shown to be pathogenic for humans as it has been isolated from human wounds and has been shown to cause primary septicimia in healthy humans.
Symptoms of Photobacteria damselae subspecies damselae
Fish infected by the subspecies damselae initially experience a reduced appetite accompanied by lethargicness and ulcerative lesions along their flank and head regions. Their stomachs will distend and they will experience extensive hemorrhaging especially in their eyes, mouth, and musculature. There will also be petechiaPetechia
A petechia is a small red or purple spot on the body, caused by a minor hemorrhage ."Petechiae" refers to one of the three major classes of purpuric skin conditions. Purpuric eruptions are classified by size into three broad categories...
tion of the gills and liver along with the characteristic accumulation of mucus around the gills. It has been noted that the infected fish will swim violently a few minutes before death occurs
Transmission/infection of Photobacterium damselae subspecies damsela
Evidence of epizooticEpizootic
In epizoology, an epizootic is a disease that appears as new cases in a given animal population, during a given period, at a rate that substantially exceeds what is "expected" based on recent experience . Epidemic is the analogous term applied to human populations...
outbreaks gained from an increase in ulcers noted among the fish populations seem to correlate to warmer seasons, suggesting a seasonal distribution in the incidence of the disease, dependant upon the waters temperature and salinity along with a decreased resistance caused by physiological changes experienced by the host during sexual maturity.
Seawater is the most likely mode of transmission of the virulent cells of the pathogen. Once it comes into contact with the outer surface of the fish, it is able to adhere to skin and resist the bactericidal action of the skin mucus layer
Mucus
In vertebrates, mucus is a slippery secretion produced by, and covering, mucous membranes. Mucous fluid is typically produced from mucous cells found in mucous glands. Mucous cells secrete products that are rich in glycoproteins and water. Mucous fluid may also originate from mixed glands, which...
, thus suggesting that the skin is the site of entry into the host. This bacterium could therefore represent a significant threat to aquacultured fish species, especially those living in crowded and stressed conditions, where the spread of the disease could be accelerated through direct contact and thus pose a threat to humans.