Vibrio fischeri NEU2011

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A page on the microorganism Vibrio fischeri

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[[File:|400px|thumb|right|Figure 1:]]


Higher order taxa

Vibrio fischeri

  • Kingdom: Bacteria
  • Phylum: Proteobacteria
  • Class: Gamma Proteobacteria
  • Order: Vibrionales
  • Family: Vibrionaceae
  • Genus: Vibrio
  • Species: V. fischeri

Description and Significance

Figure 2: The Hawaiian bobtailed squid, Euprymna scolopes. This organism is the host for Vibrio fischeri cells. The squid and V. fischeri cells share a unique, symbiotic relationship. This image is courtesy of M. J. McFall-Njai and E. G. Ruby. University of Hawii, National Science Foundation (12).

Vibrio Fischeri is a member of the phylum proteobacteria. These bacteria are motile, gram-negative rods that are found in temperate and subtropical waters. These heterotrophic bacteria use flagella as a means of movement and they are most famous for their bioluminescence properties. This bioluminescence can be seen in Figure 1. V. Fischeri is mainly found living in symbiosis with various deep sea marine animals such as monocentrid fishes and bobtail squid. It can be found within unique light-organs or as part of the normal gut of these marine animals. This bacteria can also be found living as free bacteria in small quantities surviving on decaying organic matter (11).

V. Fischeri use proteins coded by a set of genes called the lux operon to produce bioluminescence. The light is produced in a chemical reaction where luciferin is oxidized by the enzyme luciferase. As a result of the oxidation, a blue-green light is emitted. The symbiotic relationship between a strain of the V. Fischeri and its host, the bobtail squid Euprymna scolopesseen in Figure 2, has been studied extensively. The bobtail squid acquires these bacteria from its surroundings and uses it as a protection from predators. Within several hours of being ingested, these bacteria begin to change. They decrease in size, lose their flagella, and begin to emit light. These bacteria help to eliminate the squid’s shadow caused by the moonlight above (13).

The isolation and cloning of the lux gene from V. Fischeri, and their use as a reporter gene, have provided scientists with many valuable research techniques. The lux gene has enabled scientists to visually study and examine many living organisms at a cellular level. Likewise, V. Fischeri cells have been made commercially available to ecotoxicologists to detect contaminants in the environment more quickly and cheaper than most other available methods (7). V. fischeri is also the bacterium in which acyl-homoserine lactone, quorum sensing, was first discovered and described. Quorum sensing is a process that allows the bacteria to coordinate their gene expression according to the density of the population. In V. fischeri, when the bacteria have become highly concentrated in the light organs of the bobtail squid, luciferase is produced leading to bioluminescence. The discovery of quorum sensing has lead to the disclosure of many other bacteria that use this type of cell coordination process. Some bacteria such as Escherichia coli, Salmonella enterica, and Pseudomonas aeruginosa use quorum sensing (2). In addition to being the pioneering bacteria in the discovery of quorum sensing, quorum sensing in V. fischeri has lead many new research opportunities in targeting and combating bacterial infections and also has begun to be used in research to discover a way to fight cancerous tumors (1).

Genome Structure

The genome of V.fisheri contains 4273718 nucleotides, 3817 protein genes and 165 RNA genes. The chromosomes I and II are circular. The sequence of the chromosome 1 is NC_006840 and its lenght is equal to 2897536. The sequence of the chromosome II is NC_006842 and its lenght is equal to 1330333. The ES114 strain is characterized by a circular plasmid known as pES100. The number of taxonomy of the Vibrio fisheri is 312309 (KEGG).


Past studies have demonstrated that Vibrio fischeri is successful at adapting to a variety of ecological niches. They are commonly present as planktonic cells in seawater or sediments, and as saprophytes. V. fischeri are usually found in very low quantities in almost all oceans of the world, preferentially found in temperate and sub-tropical waters. They populate fecal materials. In higher concentration, V. fischeri have cooperative associations with certain deep sea marine life within special light-organs. Indeed, they can form associations with specialized symbiotic organs of marine squids and fishes (Nealson).

Although many studies have reported specific niches and predictable patterns in geographical distribution for luminous bacterial species the factors underlying their ecological dynamics is not well understood yet (Feldman). Additionally the bacteria can be pathogenic to certain species of marine invertebrates, some of which are commercially farmed in aquaculture. This disease is known as luminous vibriosis (Orndorff).

Cell Structure and Metabolism

Vibrio fischeri is a Gram-negative bioluminescent oxidase-positive marine bacterium composed of a cell wall with an outer membrane consisting of inner cytoplasmic membrane covered by peptidoglycan layer followed by periplasmic space to the lipopolysaccharides. They are straight rod with 0.8-1.3 um in diameter and 1.8-2.4um in length. The bacteria has 1-3 polar unsheathed flagella.

This bacterium is capable of respiratory and fermentative metabolism because it is a chemoorganotroph. Vibrio fischeri is a facultative anaerobe. It cannot dentrify, implying that it cannot use nitrogen in its metabolism.

The bacteria form mutually symbiotic relationships with various species of fish and squids with their ability to produce bioluminescence. The production of bioluminescence is enabled by the proteins that are encoded in a set of genes referred to as the lux operon. Light is produced when an enzyme, luciferase, oxidizes luciferin, a substrate molecule. This reaction releases free energy in the form of blue-green light at 480nm-490nm(blue-green). The reaction that occurs in Vibrio fischeri is as follows:

                 FMNH2 + RCHO + O2 --> FMN + RCOOH + H2O + hv(490nm)

The bioluminescence quantum yield has been estimated to be 10-30% according to Encyclopedia of Life Sciences (Davis, Aubrey).


Figure 3: This micrograph shows the pathogenic species of Vibrio cholera. Image courtesy of Dennis Kunkel Microscopy Incorporation(11).

Vibrio fischeri itself is non-pathogenic and is classified as a mutualistic symbiont. The V. fischeri species is known for its beneficial association with the light organ of the bobtail squid, Euprymna scolopes (14).

In the genus of Vibrio, are several dozen species known to participate in a diversity of pathogenic interactions with other organisms. Among these species are Vibrio cholerae, shown in Figure 3, Vibrio parahaemolyticus, Vibrio vulnificus, and Vibrio harveyi. V. cholerae, V. parahaemolyticus, and V. vulnificus are best known are causing illness in humans. Vibrio infections are characterized in humans as a foodborne illness. This would be due to the consumption of contaminated seafood or the exposure of an open wound to tainted seawater. Symptoms present themselves as gastroenteritis issues such as diarrhea, nausea, vomiting, and headaches. Infections due to open wound sites would include swelling at the site, pain, erythema, and necrosis. In addition to these ailments,V. vulnificus is also responsible for causing septicemia in an infected individual. Of the pathogenic species present in humans, V. vulnificus is linked with the highest fatality rate (6).

Vibrio harveyi is pathogenic to certain species of marine invertebrates and is known as luminous vibriosis. Luminous vibriosis can be found in sharks, seabass, seahorses, lobster, and shrimp. This disease forms plaques in the mouth, innards, and appendages. This causes the loss of limb function and soon after death of the organism. Luminous vibriosis is the leading cause of death for commercially farmed shrimp and other aquaculture (12).

Current Research

Vibrio fischeri has been the subject of extensive studies in physiology, biochemistry, and genetics that underlie the mechanics of bacterial bioluminescence. Past studies of V. fischeri lead to the discovery of a signaling behavior termed quorum sensing (2).

In a recent study, Environmentally Controlled Invasion of Cancer Cells by Engineered Bacteria, Anderson and his colleagues, Clarke, Arkin, and Voigt, were able to engineer bacteria that are able to target and then invade mammalian cancer cells. This is able to occur due to quorum sensing genes from the bacteria Vibrio fischeri. In this line of research, Anderson and his colleagues were able to engineer the interaction between bacteria and cancer cells to depend on heterologous environmental signals. This is made possible due to bacteria's ability to sense their environment and distinguish between different cell types. They used Escherichia coli to invade the cancer derived cells including HeLa, HepG2, and U2OS cells. Using the Vibrio fischeri lux quorum sensing circuit, the hypoxia-responsive fdhF promoter, or the arabinose-inducible araBAD promoter, researchers were able to environmentally restrict invasion of the bacteria into the cancer cells whose cells had densities greater than 10⁸ bacteria/ml. The quorum sensing genes used from V. fischeri triggered the invasion of a gene only if a cell had high numbers. The bacteria were also attracted to the cancer cells due to their hypoxic and nutrient rich microenvironments. Researchers hope that one day this finding could be used to engineer bacteria that sense the microenvironment of a tumor, invade it, and then release a cytotoxic agent that can destroy cancerous tumors (1).

Interesting Facts

Figure 4: This laser-scanning confocal micrograph shows the light organ of a newly hatched squid, Euprymna scolopes. The symbiont, V. fischeri, enters the light organ though pores on either side of the organ. These can be seen as the three small holes on the left and right side of the micrograph. This image was provided courtesy of S. Nyholm (13).

Vibrio fischeri and its symbiont Euprymna scolopes,a squid, work together to survive, thrive, and successfully reproduce. Euprymna scolopes use the bacteria V. fischeri for its bioluminescence properties. The squid is a nocturnal feeder, and uses the light generated from V. fischeri to eliminate its shadow caused by the moonlight above. Every morning, the squid releases 90% of the V. fischeri population in its light organ back into the water. This is most likely to insure that new squid populations have the bacteria available to them (9).

The squid is able to control the brightness and the direction of their illuminations produced by V. fischeri. The light sensing organs in the Euprymna scolopes shown in Figure 4,also does much more than just produce light, they are also able to sense light. Due to proteins located in the light organs, these organs are an extra set of "primitive eyes" each with their own iris and lens (4).


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