Vibrio fischeri
Encyclopedia
Vibrio fischeri is a gram-negative
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...

 rod-shaped bacterium found globally in marine
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

 environments. V. fischeri has bioluminescent
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...

 properties, and is found predominantly 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 various marine animals, such as the bobtail squid
Bobtail squid
Bobtail squid are a group of cephalopods closely related to cuttlefish. Bobtail squid tend to have a rounder mantle than cuttlefish and have no cuttlebone. They have eight suckered arms and two tentacles and are generally quite small...

. It is heterotrophic and moves by means of flagella
Flagellum
A 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...

. Free living V. fischeri survive on decaying organic matter
Organic matter
Organic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds...

 (see saprotroph). The bacterium is a key research organism for examination of microbial bioluminescence
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...

, quorum sensing
Quorum sensing
Quorum sensing is a system of stimulus and response correlated to population density. Many species of bacteria use quorum sensing to coordinate gene expression according to the density of their local population. In similar fashion, some social insects use quorum sensing to determine where to nest...

, and bacterial-animal symbiosis. It is named in honor of Bernhard Fischer
Bernhard Fischer
Johann Friedrich Bernhard Fischer was a German bacteriologist noted for his classification system for bacteria.-Biography:...

, a german microbiologist.

Ecology

Plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...

ic V. fischeri are found in very low quantities (almost undetectable) in almost all ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

s of the world, preferentially found in temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...

 and sub-tropical waters. These free-living V. fischeri subsist on organics within the water. They are found in higher concentrations in symbiosis with certain deep sea marine life within special light-organs; or as part of the normal enteral (gut) microbiota of marine animals.

Symbiotic relationship

Symbiotic relationships in monocentrid fishes and sepiolid squid
Sepiolidae
Sepiolidae is a family of bobtail squid encompassing 15 genera in three or four subfamilies....

 appear to have evolved
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

 separately. The most prolific of these relationships is with the Hawaiian bobtail squid
Hawaiian Bobtail Squid
Euprymna scolopes, also known as the Hawaiian Bobtail Squid, is a species of bobtail squid in the family Sepiolidae. It is native to the central Pacific Ocean, where it occurs in shallow coastal waters off the Hawaiian Islands and Midway Island...

 (Euprymna scolopes).

Free-living V. fischeri in the ocean inoculate the light organs of juvenile squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...

 and fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

. Ciliated cells within the light organs selectively draw in the symbiotic bacteria. These cells promote the growth of the symbionts and actively reject any competitors. The bacteria cause these cells to die off once the light organ is sufficiently colonised.

The light organ of certain squid contain reflective plates that intensify and direct the light produced, due to protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s known as reflectin
Reflectin
Reflectin is a protein originating from the Hawaiian Bobtail Squid, Euprymna scolopes, which is native to the central Pacific Ocean. Reflectins, a recently identified protein family that is enriched in aromatic and sulphur-containing amino acids, are used by certain cephalopods to manage and...

s. They regulate the light to keep the squid from casting a shadow on moonlit nights, for example. Sepolid squids expel 90% of the symbiotic bacteria in its light organ each morning in a process known as "venting". Venting is hypothesised to provide the free-living inoculum source for newly hatched squids.

It has been proposed that this microorganism be renamed as Aliivibrio fisheri http://ijs.sgmjournals.org/cgi/reprint/57/12/2823

Bioluminescence

The bioluminescence
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...

 of V. fischeri is caused by transcription
Transcription (genetics)
Transcription is the process of creating a complementary RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes...

 induced by population-dependent quorum sensing
Quorum sensing
Quorum sensing is a system of stimulus and response correlated to population density. Many species of bacteria use quorum sensing to coordinate gene expression according to the density of their local population. In similar fashion, some social insects use quorum sensing to determine where to nest...

. The luminescence
Luminescence
Luminescence is emission of light by a substance not resulting from heat; it is thus a form of cold body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions, or stress on a crystal. This distinguishes luminescence from incandescence, which is light emitted by a...

 is seen only when population density reaches a certain level.

The luminescence appears to follow a circadian rhythm
Circadian rhythm
A circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...

. That is, it is brighter during the nighttime than during the daytime.

Bioluminescence levels have also been shown to be proportionally related to both protection against ultraviolet radiation damage to gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

s and the pathogenicity of bioluminescent V. fischeri.

Genetics of bioluminescence

The bacterial luciferin
Luciferin
Luciferins are a class of light-emitting biological pigments found in organisms that cause bioluminescence...

-luciferase
Luciferase
Luciferase is a generic term for the class of oxidative enzymes used in bioluminescence and is distinct from a photoprotein. One famous example is the firefly luciferase from the firefly Photinus pyralis. "Firefly luciferase" as a laboratory reagent usually refers to P...

 system is encoded by a set of genes labelled the Lux operon. In V. fischeri, five such genes (LuxCDABE) have been identified as active in the emission of visible light, and two genes (LuxR and LuxI) are involved in regulating the operon
Operon
In genetics, an operon is a functioning unit of genomic DNA containing a cluster of genes under the control of a single regulatory signal or promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo trans-splicing to create...

. Several external and intrinsic factors appear to induce and inhibit the transcription of this gene set and produce or suppress light emission. More research is being done to improve our understanding of these processes.

The bioluminescent gram-negative bacterium Vibrio fischeri is one of many branches of bacteria that commonly form symbiotic relationships with marine organisms (Distal, 1993). It has been researched that marine organisms contain bacteria that utilize bioluminescence so that the organism can find mates, ward off predators, attract prey, or communicate with other organisms (Widder, 2010). In return, the organism the bacteria are living within provides the bacteria with a nutrient-rich environment (Winfrey et al., 1997).
The lux operon is a 9-kilobase fragment of the V. fischeri genome that controls bioluminescence through the catalyzation of the enzyme luciferase (Meighen, 1991). The lux operon has a known gene sequence of luxCDAB(F)E, where lux A and lux B code for the components of luciferase, and the lux CDE codes for a fatty acid reductase complex that makes the fatty acids necessary for the luciferase mechanism (Meighen, 1991). Lux C codes for the enzyme acyl-reductase, lux D codes for acyl-transferase, and lux E makes the proteins needed for the enzyme acyl-protein synthetase. Luciferase produces blue/green light through the oxidation of reduced flavin mononucleotide and a long-chain aldehyde by diatomic oxygen. The reaction is summarized below (Silverman et al., 1984):
FMNH2+O2+R-CHO → FMN + R-COOH + H2O + Light
In order to generate the aldehyde needed in the reaction above, three additional enzymes are needed. The fatty acids needed for the reaction are pulled out from the fatty acid biosynthesis pathway by the enzyme acyl-transferase. Acyl-transferase reacts with acyl-ACP to release R-COOH, a free fatty acid. R-COOH is reduced by a two-enzyme system to an adehyde. The reaction is shown below:
R-COOH+ATP+NADPH→ R-CHO+AMP+PP+NADP+ (Winfrey et al., 1997).
Although the lux operon encodes the enzymes necessary for the bacteria to glow, bioluminescence is regulated by autoinduction. An autoinducer is a transcriptional promoter of the enzymes necessary for bioluminescence. Before the glow can be luminized, a certain concentration of an autoinducer must be present. So, in order for bioluminescence to occur, high colony concentrations of Vibrio fischeri should be present in the organism (Winfrey et al., 1997).

List of synonyms

  • Achromobacter fischeri (Beijerinck 1889) Bergey et al. 1930
  • Bacillus fischeri (Beijerinck 1889) Trevisan 1889
  • Bacterium phosphorescens indigenus (Eisenberg 1891) Chester 1897
  • Einheimischer Leuchtbacillus Fischer 1888
  • Microspira fischeri' (Beijerinck 1889) Chester 1901
  • Microspira marina (Russell 1892) Migula 1900
  • Photobacterium fischeri Beijerinck 1889
  • Vibrio noctiluca Weisglass and Skreb 1963
From NCBI Taxbrowser

External links

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