''Aliivibrio fischeri'' (also called ''Vibrio fischeri'') is a

Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

rod-shaped A bacillus (), also called a bacilliform bacterium or often just a rod (when the context makes the sense clear), is a rod-shaped bacterium or archaeon. Bacilli are found in many different taxonomic groups of bacteria. However, the name '' Baci ...

bacterium Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

found globally in marine environments. This species has bioluminescent properties, and is found predominantly in

symbiosis Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...

with various marine animals, such as the Hawaiian bobtail squid. It is

heterotrophic A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

, oxidase-positive, and

motile Motility is the ability of an organism to move independently, using metabolic energy. Definitions Motility, the ability of an organism to move independently, using metabolic energy, can be contrasted with sessility, the state of organisms th ...

by means of a single polar flagella. Free-living ''A. fischeri'' cells survive on decaying organic matter. The bacterium is a key research organism for examination of microbial

bioluminescence Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some b ...

quorum sensing In biology, quorum sensing or quorum signalling (QS) is the ability to detect and respond to cell population density by gene regulation. As one example, QS enables bacteria to restrict the expression of specific genes to the high cell densities at ...

, and bacterial-animal symbiosis. It is named after

Bernhard Fischer Johann Friedrich Bernhard Fischer (19 February 1852 Coburg - 2 August 1915 Dadizele) was a German bacteriologist noted for his classification system for bacteria. Biography After attending Casimirianum from 1862 to 1871, he was educated at the ...

, a German microbiologist.

Ribosomal RNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosomal ...

comparison led to the reclassification of this species from genus ''

Vibrio ''Vibrio'' is a genus of Gram-negative bacteria, possessing a curved-rod (comma) shape, several species of which can cause foodborne infection, usually associated with eating undercooked seafood. Being highly salt tolerant and unable to survive ...

'' to the newly created ''

Aliivibrio ''Aliivibrio'' is a genus in the phylum Pseudomonadota (Bacteria). Etymology The name ''Aliivibrio'' derives from: Latin ', other, another, different; New Latin ''Vibrio'', a bacterial genus name, to give ''Aliivibrio'', the other ''Vibrio''. S ...

'' in 2007. However, the name change is not generally accepted by most researchers, who still publish ''Vibrio fischeri'' (see Google Scholar for 2018-2019).

Genome

The

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...

for ''A. fischeri'' was completely

sequenced In genetics and biochemistry, sequencing means to determine the primary structure (sometimes incorrectly called the primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which suc ...

in 2004 and consists of two

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

s, one smaller and one larger. Chromosome 1 has 2.9 million

base pair A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both DNA ...

s (Mbp) and chromosome 2 has 1.3 Mbp, bringing the total genome to 4.2 Mbp. ''A. fischeri'' has the lowest

G+C content G, or g, is the seventh letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''gee'' (pronounced ), plural ''gees''. History Th ...

of 27 ''Vibrio'' species, but is still most closely related to the higher-pathogenicity species such as '' V. cholerae.'' The genome for ''A. fischeri'' also carries

mobile genetic elements Mobile genetic elements (MGEs) sometimes called selfish genetic elements are a type of genetic material that can move around within a genome, or that can be transferred from one species or replicon to another. MGEs are found in all organisms. In ...

Ecology

''A. fischeri'' are globally distributed in

temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...

and

subtropical The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Geographical z ...

marine environments. They can be found free-floating in oceans, as well as associated with marine animals, sediment, and decaying matter. ''A. fischeri'' have been most studied as symbionts of marine animals, including

squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...

s in the genus ''

Euprymna ''Euprymna'' is a genus of bobtail squid comprising a number of species. Species *'' Euprymna albatrossae'' (Voss, 1962) *'' Euprymna berryi'' (Sasaki, 1929), double-ear bobtail *''Euprymna brenneri'' (Sanchez et al., 2019) *''Euprymna bursa'' * ...

'' and '' Sepiola'', where ''A. fischeri'' can be found in the squids' light organs. This relationship has been best characterized in the Hawaiian Bobtail Squid (''Euprymna scolopes''), where ''A. fischeri'' is the only species of bacteria inhabiting the squid's light organ.

Symbiosis with the Hawaiian bobtail squid

''A. fischeri'' colonization of the light organ of the Hawaiian bobtail squid is currently studied as a simple model for mutualistic symbiosis, as it contains only two species and ''A. fischeri'' can be cultured in a lab and genetically modified. This mutualistic symbiosis functions primarily due to ''A. fischeri'' bioluminescence. ''A. fischeri'' colonizes the light organ of the Hawaiian bobtail squid and luminesces at night, providing the squid with counter-illumination camouflage, which prevents the squid from casting a shadow on the ocean floor. ''A. fischeri'' colonization occurs in juvenile squids and induces morphological changes the squids light organ. Interestingly, certain morphological changes made by ''A. fischeri'' do not occur when the microbe cannot luminesce, indicating that bioluminescence (described below) is truly essential for symbiosis. In the process of colonization,

cilia The cilium, plural cilia (), is a membrane-bound organelle found on most types of eukaryotic cell, and certain microorganisms known as ciliates. Cilia are absent in bacteria and archaea. The cilium has the shape of a slender threadlike projecti ...

ted cells within the animals'

photophore A photophore is a glandular organ that appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors, ...

s (light-producing 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 colonized. The light organs of certain squid contain reflective plates that intensify and direct the light produced, due to

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s known as

reflectin Reflectins are a family of intrinsically disordered proteins evolved by a certain number of cephalopods including ''Euprymna scolopes'' and ''Doryteuthis opalescens'' to produce Iridescence, iridescent camouflage and signaling. The recently identi ...

s. They regulate the light for

counter-illumination Counter-illumination is a method of active camouflage seen in marine animals such as firefly squid and midshipman fish, and in military prototypes, producing light to match their backgrounds in both brightness and wavelength. Marine animals of ...

camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the ...

, requiring the intensity to match that of the sea surface above. Sepiolid squid expel 90% of the symbiotic bacteria in their light organ each morning in a process known as "venting". Venting is thought to provide the source from which newly hatched squid are colonized by ''A. fischeri''.

Bioluminescence

The

of ''A. fischeri'' is caused by

transcription Transcription refers to the process of converting sounds (voice, music etc.) into letters or musical notes, or producing a copy of something in another medium, including: Genetics * Transcription (biology), the copying of DNA into RNA, the fir ...

of the ''lux'' operon, which is induced through population-dependent

. The population of ''A. fischeri'' needs to reach an optimal level to activate the ''lux'' operon and stimulate light production. The

circadian rhythm A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., Endogeny (biology), endogeno ...

controls light expression, where luminescence is much brighter during the day and dimmer at night, as required for camouflage. The bacterial

luciferin Luciferin (from the Latin ''lucifer'', "light-bearer") is a generic term for the light-emitting compound found in organisms that generate bioluminescence. Luciferins typically undergo an enzyme-catalyzed reaction with molecular oxygen. The result ...

luciferase Luciferase is a generic term for the class of oxidative enzymes that produce bioluminescence, and is usually distinguished from a photoprotein. The name was first used by Raphaël Dubois who invented the words ''luciferin'' and ''luciferase'', ...

system is encoded by a set of genes labelled the ''lux'' operon. In ''A. fischeri'', five such genes (''luxCDABEG'') have been identified as active in the emission of visible light, and two genes (''luxR'' and ''luxI'') are involved in regulating the

operon In genetics, an operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo splic ...

. Several external and intrinsic factors appear to either induce or

inhibit Inhibitor or inhibition may refer to: In biology * Enzyme inhibitor, a substance that binds to an enzyme and decreases the enzyme's activity * Reuptake inhibitor, a substance that increases neurotransmission by blocking the reuptake of a neurotr ...

the transcription of this gene set and produce or suppress

light emission This is a list of sources of light, the visible part of the electromagnetic spectrum. Light sources produce photons from another energy source, such as heat, chemical reactions, or conversion of mass or a different frequency of electromagnetic ener ...

. ''A. fischeri'' is one of many species of bacteria that commonly form symbiotic relationships with marine organisms. Marine organisms contain bacteria that use bioluminescence so they can find mates, ward off predators, attract prey, or communicate with other organisms. In return, the organism the bacteria are living within provides the bacteria with a nutrient-rich environment. The ''lux'' operon is a 9-kilobase fragment of the ''A. fischeri'' genome that controls bioluminescence through the catalytic activity of the enzyme luciferase.(Meighen, 1991). This operon has a known gene sequence of ''luxCDAB(F)E'', where ''luxA'' and ''luxB'' code for the protein subunits of the luciferase enzyme, and the ''luxCDE'' codes for a fatty acid reductase complex that makes the

fatty acid In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, fr ...

s necessary for the luciferase mechanism.'' luxC ''codes for the enzyme acyl-reductase, ''luxD'' codes for acyl-transferase, and ''luxE'' makes the proteins needed for the enzyme acyl-protein synthetase. Luciferase produces blue/green light through the oxidation of reduced

flavin mononucleotide Flavin mononucleotide (FMN), or riboflavin-5′-phosphate, is a biomolecule produced from riboflavin (vitamin B2) by the enzyme riboflavin kinase and functions as the prosthetic group of various oxidoreductases, including NADH dehydrogenase, as ...

and a long-chain

aldehyde In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...

diatomic oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing agent that readily forms oxides with mos ...

. The reaction is summarized as: :FMNH₂ + O₂ + R-CHO → FMN + R-COOH + H₂O + light. The reduced flavin mononucleotide (FMNH) is provided by the ''fre'' gene, also referred to as ''luxG''. In ''A. fischeri'', it is directly next to ''luxE'' (giving ''luxCDABE-fre'') from 1042306 to 104874

To generate the aldehyde needed in the reaction above, three additional enzymes are needed. The fatty acids needed for the reaction are pulled from the fatty acid biosynthesis pathway by acyl-transferase. Acyl-transferase reacts with acyl- Acyl carrier protein, ACP to release R-COOH, a free fatty acid. R-COOH is reduced by a two-enzyme system to an aldehyde. The reaction is: :R-COOH + ATP + NADPH → R-CHO + AMP + PP + NADP⁺.

Quorum Sensing

One primary system that controls bioluminescence through regulation of the ''lux''

, a conserved system across many microbial species that regulates gene expression in response to bacterial concentration. Quorum sensing functions through the production of an

autoinducer Autoinducers are signaling molecules that are produced in response to changes in cell-population density. As the density of quorum sensing bacterial cells increases so does the concentration of the autoinducer. Detection of signal molecules by ba ...

, usually a small organic molecule, by individual cells. As cell populations increase, levels of autoinducers increase, and specific proteins that regulate transcription of genes bind to these autoinducers and alter gene expression. This system allows microbial cells to "communicate" amongst each other and coordinate behaviors like luminescence, which require large amounts of cells to produce an effect. In ''A. fischeri'', there are two primary quorum sensing systems, each of which respond to slightly different environments. The first system is commonly referred to as the ''lux'' system, as it is encoded within the ''lux'' operon, and uses the autoinducer 3OC6-HSL. The protein LuxI synthesizes this signal, which is subsequently released from the cell. This signal, 3OC6-HSL, then binds to the protein LuxR, which regulates the expression of many different genes, but is most known for upregulation of genes involved in luminescence. The second system, commonly referred to as the ''ain'' system, uses the autoinducer C8-HSL, which is produced by the protein AinS. Similar to the ''lux'' system, the autoinducer C8-HSL increases activation of LuxR. In addition, C8-HSL binds to another transcriptional regulator, LitR, giving the ''ain'' and ''lux'' systems of quorum sensing slightly different genetic targets within the cell. The different genetic targets of the ''ain'' and ''lux'' systems are essential, because these two systems respond to different cellular environments. The ''ain'' system regulates transcription in response to intermediate cell density cell environments, producing lower levels of luminescence and even regulating metabolic processes like the acetate switch. On the other hand, the ''lux'' quorum sensing system occurs in response to high cell density, producing high levels of luminescence and regulating the transcription of other genes, including QsrP, RibB, and AcfA. Both of the ''ain'' and ''lux'' quorum sensing systems are essential for colonization of the squid and regulate multiple colonization factors in the bacteria. Activation of the lux operon in Aliivibrio fischeri

Activation of the lux operon in Aliivibrio fischeri

Natural transformation

Natural bacterial

transformation Transformation may refer to: Science and mathematics In biology and medicine * Metamorphosis, the biological process of changing physical form after birth or hatching * Malignant transformation, the process of cells becoming cancerous * Trans ...

is an adaptation for transferring DNA from one individual cell to another. Natural transformation, including the uptake and incorporation of exogenous DNA into the recipient

, has been demonstrated in ''A. fischeri''. This process requires induction by chitohexaose and is likely regulated by genes ''tfoX'' and ''tfoY''. Natural transformation of ''A. fischeri'' facilitates rapid transfer of mutant genes across strains and provides a useful tool for experimental genetic manipulation in this species.

State microbe status

In 2014, Hawaiian State Senator

Glenn Wakai Glenn S. Wakai (born May 14, 1967) is an American politician and a Democratic member of the Hawaii Senate since January 2011 representing District 15. Wakai consecutively served in the Hawaii State Legislature where he served from 2003 until 2 ...

submitted SB3124 proposing ''Aliivibrio fischeri'' as the

state microbe A state microbe is a microorganism used as an official state symbol. Several U.S. states have honored microorganisms by nominating them to become official state symbols. The first state to declare an Official State Microbe is Oregon which chose ' ...

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only stat ...

. The bill was in competition with a bill to make ''

Flavobacterium akiainvivens ''Flavobacterium akiainvivens'', or koohonua ili akia, (literally "ākia bark bacteria") is a species of gram-negative bacteria in the Flavobacteriaceae family. The specific epithet ''akiainvivens'' is Latin (') and literally means "living on or ...

'' the state microbe, but neither passed. In 2017, legislation similar to the original 2013 ''F. akiainvivens'' bill was submitted in the

Hawaii House of Representatives The Hawaii House of Representatives is the lower house of the Hawaii State Legislature. Pursuant to Article III, Section 3 of the Constitution of Hawaii, amended during the 1978 constitutional convention, the House of Representatives consis ...

Isaac Choy Isaac W. Choy is an American politician and a former Democratic member of the Hawaii House of Representatives representing District 23 from January 2013 to January 2019. Choy consecutively served from 2009 until 2013 in the District 24 seat. I ...

and in the

Hawaii Senate The Hawaii Senate is the upper house of the Hawaii State Legislature. It consists of twenty-five members elected from an equal number of constituent districts across the islands and is led by the President of the Senate, elected from the membe ...

Brian Taniguchi Brian T. Taniguchi (born November 7, 1951 in Honolulu, Hawaii) is an American politician and a Democratic member of the Hawaii Senate since January 16, 2013 representing District 10. Taniguchi served consecutively from 1995 until 2013 in the Dis ...

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

References

External links

The Light-Organ Symbiosis of ''Vibrio fischeri'' and the Hawaiian squid, ''Euprymna scolopes''
* ttp://www.ted.com/talks/bonnie_bassler_on_how_bacteria_communicate.html TED Talks - Bonnie Bassler on how bacteria communicate {{Taxonbar, from=Q148731 Vibrionales Bacteria described in 1896 Bioluminescent bacteria Model organisms Symbiosis