Photobacterium

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Photobacterium
Scientific classification Edit this classification
Domain: Bacteria
Phylum: Pseudomonadota
Class: Gammaproteobacteria
Order: Vibrionales
Family: Vibrionaceae
Genus: Photobacterium
Species

P. angustum
P. aplysiae
P. carnosum
P. damselae

P. fischeri

P. frigidiphilum
P. ganghwense
P. halotolerans
P. histaminum
P. iliopiscariumal
P. indicum
P. leiognathi
P. lipolyticum
P. logei
P. marinum
P. phosphoreum
P. profundum
P. rosenbergii

Photobacterium is a genus of

bioluminescent, that is they have the ability to emit light
.

Many species, including Photobacterium leiognathi and Photobacterium phosphoreum, Photobacterium ganghwense, Photobacterium marinum live in symbiosis with marine organisms.[1] S.I. Paul et al. (2021)[1] isolated and identified multiple strains of Photobacterium from marine sponges of the Saint Martin's Island Area of the Bay of Bengal, Bangladesh.

Species such as Photobacterium profundum are adapted for optimal growth in the deep cold seas making it both a psychrophile (an organism capable of growth and reproduction in cold temperatures) and a piezophile (an organism which thrives at high pressures).

Biochemical characteristics of Photobacterium species

Colony, morphological, physiological, and biochemical characteristics of Photobacterium species are shown in the Table below.[1]

Test type Test Characteristics
Colony characters Size Medium
Type Round
Color Creamy
Shape Convex
Morphological characters Shape Rod
Physiological characters Motility +
Growth at 6.5% NaCl +
Biochemical characters Gram's staining –
Oxidase +
Catalase +
Oxidative-Fermentative Oxidative
Motility +
Methyl Red +
Voges-Proskauer –
Indole +
H2S Production –
Urease V
Nitrate reductase +
β-Galactosidase –
Hydrolysis of Gelatin +
Aesculin V
Casein V
Tween 40 +
Tween 60 +
Tween 80 +
Acid production from Glycerol +
Galactose +
D-Glucose +
D-Fructose V
D-Mannose –
Mannitol V
N-Acetylglucosamine V
Amygdalin +
Maltose V
D-Melibiose +
D-Trehalose +
Glycogen V
D-Turanose V

Note: + = Positive; – =Negative; V =Variable (+/–)

Taxonomy

There are currently 16 species with numerous subspecies known within the genus Photobacterium.[2] The development of 16S RNA sequencing has led to many species being shifted into and out of this genus.[3] 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 flagella
  • Are luminescent
  • Incapable of forming resistant
    endospores
  • Are
    chemoorganotrophs

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 autoinducers 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.[3]

Pathogenicity

Some of the 15 known species of Photobacterium have evolved into

Seabreams (Sparus spp.), Striped bass (Morone saxatilis), and White perch (Morone americana). This subspecies is not pathogenic for humans.[5]

Photobacterium damselae subspecies damsela

Fish-virulent strains of this subspecies of P. damselae cause

Seriola 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.[6]

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 petechiation 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 epizootic 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, dependent 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.[7]

See also

  • Vibrio fischeri

References

  1. ^
    ISSN 0044-8486
    .
  2. ^ "Results for "Photobacterium"". Catalogue of Life. University of Reading, Reading, UK: The Species 2000 & ITIS. December 5, 2011. Archived from the original on September 13, 2019. Retrieved January 23, 2012.
  3. ^ a b "Photobacterium Species". filebox.vt.edu. Archived from the original on 2014-12-24. Retrieved 2011-04-27.
  4. PMID 10843555
    .
  5. doi:10.1111/j.1749-7345.2009.00251.x
    .
  6. ^ Austin. Bacterial Fish Pathogens:Disease of Farmed and Wild Fish; 4th Edition.
  7. S2CID 30187907
    .

Hilgarth, Maik et al. “Photobacterium Carnosum Sp. Nov., Isolated from Spoiled Modified Atmosphere Packaged Poultry Meat.” Systematic and Applied Microbiology 41.1 (2018): 44–50.

External sources
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