The Communication Between Vibrio Fischeri and it’s Marine Life Host

As I have discussed in my previous blogs, Vibrio fischeri makes the ocean squid Euprymna Scolopes it’s host. They have an interesting symbiotic relationship as the squid provides the antimicrobial with a place to colonize and thrive, whileVibrio fischeri causes the squid to glow in the dark through a process called bioluminescence!

So how exactly do these two creatures communicate and interact with each other to come together in this seemingly perfect harmony?


The light organ within the squid is not exposed on the surface of its body. Therefore, the bacterium has to detect the presence of the squid and try to move in close. From this point, the squid filters seawater through its mental cavity conveniently collecting V.Fischeriin the process.

Once inside the squid the bacteria get stuck along the cilia and mucous lining the inside of the squid. This actually aids Vibrio fischeri in its quest to reach the squid’s light organ since the sticking to the walls allows the bacteria to aggregate into a single mass, allowing a biofilm to form.

The 18 gene sypis responsible for encoding proteins that maintain and transport the mass towards the light organ within the squid. While this is extremely intriguing and only adds more questions to my mind regarding this cellular process, the mechanism of this process independent of the syp gene is still mostly unknown.

Then, once they aggregate and reaches the light organ, the individual bacterial cells have to migrate from their biofilm and enter their specific sites within the organ. In order to do this, the Vibrio fischeri use flagella for movement and chemotaxis to direct their movement. If this did not sound like enough of a challenge for this bacterium, it also has to flee against the squid’s immune system and biological processes that may be potentially lethal to the bacteria.


The squid host contains enzymes that produce reactive oxygen species within the organism. One, in particular, Hydrogen Peroxidase converts Hydrogen Peroxide into Hypochlorous Acid, a chemical toxic to the Vibrio fischeri. To combat against this, the bacteria contain a gene expression katA that causes an increase in the sensitivity to Hydrogen Peroxide. This allows the bacteria to steer itself away from potentially dangerous areas within the organism.

Additionally, when Vibrio fischeri starts to colonize the light organ within the squid the levels of Hydrogen Peroxidase decrease, but the mechanism behind this process is still unknown.

 Finally, after all of this struggle, the bacterium is able to enter the organ and start its colonization process. Protected from the dangers of the ocean and lighting up the squid from within. This process is truly mesmerizing, and I hope there is further research on the unknown processes in the future.





Lastly, I would like to leave here one of my favorite episode of  TED Talks:


Hope you guys enjoyed learning with me. 



  2. Doino, J.A., and M. J. McFall-Ngai. 1995. A transient exposure to symbiosis-competent bacteria induces light-organ morphogenesis in the host squid. Biol. Bull. 189:347-355.
  3. “V. Fischeri.” Strain Info. Genomic Standards Consortium, n.d. Web. 25 Oct. 2011. <>.
  5. Fidopiastis PM, Miyamoto CM, Jobling MG, Meighen EA, Ruby EG. 2002. LitR, a new transcriptional activator in Vibrio fischeri, regulates luminescence and symbiotic light organ colonization. Mol. Microbiol. 45:131-43.
  7. Ruby, E. G. and M. Urbanowski. 2004. Complete genome sequence of Vibrio fischeri: A symbiotic bacterium with pathogenic congeners. PNAS 102: 3004-3009.


Understanding More of Vibrio’s Fischeri Life Cycle

Now, that we have a better understanding of this organism itself, it is time to further understand it’s life cycle.

Vibrio fischeri are usually found in marine subtropical waters as well as freshwater. Even though my previous posts were more focused in the Vibrio fischeri living in a symbiotic relationship with the bobtail squid, this organism is also capable of free-living; they just happen to be more commonly found living in symbiosis. However, the emittance of light through quorum sensing only occurs when this bacterium is living in colonies.



But You might ask:

“How do the bacteria find the squid or vice versa?”

Bobtail squid offspring are not hatched with the bacteria, they have to “get” them from their surroundings. In fact, within minutes after being hatched the squid will acquire millions of Vibrio fischeri. The fascinating part of all of this to me is that newborn squids will produce reactive oxygen species (ROS) in order to prevent the attachment of bacterium other than Vibriofisheri.

 In the same manner, the Vibrio fischeri bacterium present in the surrounding will trigger the new hatch squid into secreting mucus from the appendage of its light organ, and then Vibrio fischeri which is attracted to the mucus components will display chemotaxis moving towards the light organ for attachment. Upon attachment, will occur the colonization phase, where the light organ will by the beginning of the night be completely formed and functional.

With the night, comes the moon, with the moon, comes the light and shadow. So, the light organ allows the bobtail squid to disguise and not cast a shadow, making them a less visible prey for its predators and making them a greater predator for its prey. More food for the bobtail squid also means more nutrients for the Vibrio fischeri, making them a perfect partner for a happy mutualistic symbiotic relationship. 

But, as we all know, happiness does not last forever, in this case, it only lasts until the morning arrives. Furthermore, the bobtail squid will expel (yes, kick them out) 95 % percent of the Vibrio fischeri. The reason, why it leaves approximately 5% is to facilitate the replication of more Vibrio fischeri which by the night time will have covered the light organ all over again, instead of having to get them again from its surrounding.

This indicates, that Vibrio fischeri are capable of replicating fast but it still not known the exact growth rate constant for its natural habitat but when mimicking its natural environment in the laboratory the results are the following. In favorable conditions, with the perfect salt and iron concentration, the bacterium takes advantage of its short generation time, in the lab when media mimics its natural habitat the growth rate constant is K= 1.2738. 

In addition, Vibrio fischeri is a relatively easy bacterium to culture in the laboratory setting since they do not need high ending apparatus to do so. They are facultative anaerobes, capable of respiratory and fermentative metabolism making them chemoorganotrophic. So, in the lab, the exposure to oxygen will positively affect them and their optimal growth temperature occurs at room temperature which is not hard to provide. Moreover, it is possible to maintain their bioluminescent glow by subculturing them 2 to 3 times per week in photobacterium agar.

Vibrio fischeri, is considered a heterotrophic bacterium which means that they are not capable of producing its own food by carbon fixation and needs to consume sources of organic carbon for nutrition. Since, most of them live in symbiotic relationship with marine organism their nutrient source depends in what kind of host they are, for example, the ones that reside in the bobtail squids receives nutrients that can vary from brine shrimp, mosquitofish, and prawns.

One interesting fact the nutrition of Vibrio fischeri is that they require an intake of iron because iron is a key growth factor and seems to play a role in the regulation of bioluminescence. Moreover, how the iron helps in the regulation is currently being further studied, but there is a hypothesis that the iron helps in the regulation through inhibiting the synthesis of luciferase which is the enzyme responsible for bioluminescence ability of the organism.

Vibrio fischeri reproduces by binary fission. In the process, a single cell will further divide into two identical daughter cells, followed by the same process over and over by the daughter cells (personally, I find fascinating how bacteria can reproduce through basically making clones of themselves). 

Vibrio fischeri does not have a unique enzyme in the context of replication. However, like briefly mentioned before they have a unique gene calledLuxthat synthesizes autoinducers. Upon release of these autoinducers, it will help the bacteria to “determine” cell density. The higher the concentration for autoinducers the higher the cell density. The same autoinducers will bind to a regulatory gene in which will turn it on the Lux lac operon genes to synthesize the luciferase, which is their unique enzyme that catalyzes a redox reaction in which the byproduct is light.



FIGURE 6. Lux pathway controlling bioluminescence in V. fischeri. At low cell density, the sensor kinases AinR and LuxP/Q are predicted to exhibit net kinase activity leading to the phosphorylation of LuxU and subsequent phosphotransfer to LuxO. Phospho-LuxO induces the expression of the inhibitory sRNA, qrr1, which leads to the degradation of litR mRNA. LitR is the transcriptional activator of luxR, which encodes a protein required for expression of the luxCDEBAG operon. Thus, at low cell density, litR translation is inhibited and the cells do not produce high levels of light. At high cell density, two distinct autoinducer molecules made by AinS (C8-HSL, diamonds) and LuxS (AI-2, circles) are predicted to be at sufficient concentrations to switch the activity of the SKs from net kinase to net phosphatase activity. This leads to dephosphorylation of the downstream regulators, litR translation, and transcription of luxR. LuxR, in conjunction with the autoinducer produced by LuxI (3-oxo-C6-HSL, triangles), leads to the transcription of the lux operon and bioluminescence (reviewed in Stabb et al., 2008). LuxR is also predicted to weakly bind to C8-HSL, which allows for the initiation of luxCDABEG expression. See text for caveats to this model.


Now, last observation:

“How cool it would be if we were able to auto-induce ourselves into expressing cool genes like that?”



I hope you enjoyed learning with me


See you guys soon.




  1. Doino, J.A., and M. J. McFall-Ngai. 1995. A transient exposure to symbiosis-competent bacteria induces light-organ morphogenesis in the host squid. Biol. Bull. 189:347-355.
  2. Fidopiastis PM, Miyamoto CM, Jobling MG, Meighen EA, Ruby EG. 2002. LitR, a new transcriptional activator in Vibrio fischeri, regulates luminescence and symbiotic light organ colonization. Mol. Microbiol. 45:131-43.
  3. Ruby, E. G. and M. Urbanowski. 2004. Complete genome sequence of Vibrio fischeri: A symbiotic bacterium with pathogenic congeners. PNAS 102: 3004-3009.
  4. “V. Fischeri.” Strain Info. Genomic Standards Consortium, n.d. Web. 25 Oct. 2011. <>.




More About Vibrio Fischeri

I recently visited the Georgia Aquarium and fell in love with one of the bacterial species I encountered by the name of Vibrio Fischeri. I have discovered so many interesting things regarding the cellular structures and chemical mechanisms within this microorganism that I cannot wait to share with you.

This micrograph shows fluorescently stained Vibrio fischeri cells. Image taken by E Nelson and L Sycuro, provided courtesy of the Vibrio fischeri Genome Project.

 This interesting microbe has a rod shape, is approximately 0.8-1.3 micrometers in diameter and 1.8-2.4 micrometers in length. They can travel through the ocean and other liquid mediums using 1 to 3 polar unsheathed flagella on the surface of their outer membrane. Vibrio Fischeri is also a unicellular microbe. A unique feature of this unicellular bacterium is that they can assemble and colonize an entire functional organ within the Bobtail Squid. This microbe consists of two chromosomes, and their genome has been fully sequenced. Within both chromosomes, there are 4,284,050 base pairs with approximately 1129 base pairs per gene. In total, this bacterium has around 3,800 genes! Additionally, the cell is oxidase-positive and classified as gram-negative with a thick peptidoglycan layer surrounding a cytoplasmic membrane.

Genome maps of Chr I (2.9 Mbp) and Chr II (1.3 Mbp) of V. fischeri ES114. (From the inside) Ring 1, rrn operons (red); tRNAs (green). Ring 2, “foreign” elements (black). Ring 3, type IV pilus loci (red). Circle 1, G+C content over a 200-kb window with 5-kb steps; red and blue denote G+C content higher and lower than average, respectively. Circle 2, homology on + and – strands to V. cholerae N16961 ORFs, determined by using FASTA; red, e value < -30; green, e value > -30. Circle 3, location in kilobases.

 One of the unique and fascinating components of this bacterium is its ability to produce bioluminescence. This component makes the Bobtail Squid one of the most mesmerizing creatures in the depths of the ocean! The Bobtail Squid has appendages on its side that find and filter these bacteria through its body to its light organ. Once these bacteria find the correct organ within the Squid, they shed their flagella to create a better surface area for attachment to the organ. Within the Vibrio Fischeri genome, there is a gene called the lux operon which encodes the enzyme named luciferase. Luciferase catalyzes a reaction that produces the light that the Bobtail Squid emits to avoid predators.

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).


 These microorganisms are a significant focus of study within marine biology, physiology, biochemistry, and even ecology as we find out more about how these bacteria can adapt to a wide variety of ecological niches, and further study the processes behind bioluminescence. I am excited to further learn and discover what Vibrio Fischeri have to offer Bobtail Squids and the world!



Here are some intriguing videos on the Bobtail Squid and its Bacterium. Check them out if you would like to learn more:












The Light at the end of the tunnel Ocean (Vibrio Fischeri)

Ever since I was a little girl, I have been fascinated by the immense variety of life that exists within the depths of the ocean. When I first moved to Georgia from Brazil I wanted to visit the Georgia Aquarium. It seemed like everyone I talked to had such a positive reflection of their experience there. As a college student, however, I kept pushing it off due to a lack of time and money. It was not until I discovered that the aquarium was one of the options given in my microbiology course that I decided I should finally visit! I am thrilled that I went. The Georgia Aquarium was a wonderful experience filled with overwhelming visual stimulation from start to finish.

Moreover, during my visit day at the aquarium I did not use a tour guide I just explored on my own, and I am so glad I did because I was able to look at everything without no rush. To me, that is one of the reasons why my experience was so pleasant because I could read every poster and learn about all the sections in each gallery.

During my visit, I learned that there are more than 10 million gallons of fresh and marine water in total in the aquarium. The aquarium divides their exhibits into seven total galleries being: Aquanaut Adventure, Cold Water Quest, Ocean Voyager Built by The Home Depot, SunTrust Pier 225, Southern Company River Scout, Tropical Diver, and AT&T Dolphin Coast. In every corner of the aquarium, there was an interesting organism; which was interfering with my decision-making process in selecting a specific organism to learn more about. However, as soon as I found the bobtail squid and about its mutually beneficial relationship with the bacteria Vibrio fischeri I knew I had my organism.

Domain: Eubacteria
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Gammaproteobacteria
Order: Vibrionales
Family: Vibrionaceae
Genus: Vibrio
Species: Fischeri


When the moons reflect its light in the sea it crosses the water deep into the ocean, if the light is not able to cross the body of an organism it will generate a shadow, and well that is not good if they do not want to be someone’s dinner. So, many marine organisms have their ways to disguise and hide from predators. In this blog, we will learn how the bioluminescent bacteria Vibrio fischeri helps the bobtail squid to not cast a shadow making them a successful predator at night.

Vibrio fischeri is a gram-negative bacterium that is naturally found mostly in seawater and sometimes in fresh water as well; they are a kind of bioluminescent bacterium and they are usually found in a symbiotic relationship with marine animals and bobtail squid is only one of them. More specifically, they offer their ability to have a bioluminescent organ that emits light in which neutralizes the light reflected by the moon in ocean floors and allow the bobtail squid to move around without casting a shadow, camouflaging, therefore, being a successful predator at night. In exchange, the bacterium that forms this light organ gets a nutrient-rich and stable environment for attachment. Their bioluminescence is possible due to the expression of a set of genes known as the lux operon. In order to communicate and synchronize the light at the same time, this bacterium is regulated by LuxR-LuxI quorum-sensing system.

The reason why I became intrigued with this bacterium is that, like any other bacteria, they do behave quite differently depending on its environment, but most intriguing is that when they are living freely they are not bioluminescent that means that they do not produce light at all. However, when they attach to form biofilms they start to secrete autoinducers resulting in the increase of cell density to form this light organ in which will eventually produce light.

In addition, one of the reasons why this bacterium stands out from another organism to me is because it changed the way I perceive bacterium processes. For example, before knowing about this bacterium I would think of quorum sensing as something negative because often times they release toxins that can be pathogenic to us humans. But now, I think that quorum sensing can be just as beautiful as it can be fatal; because not only they are able to cause death, they are also able to emit something so beautiful such as light.

Since in the aquarium I was not able to take a picture of a Bobtail squid I will leave below my favorites youtube videos about this amazing organism:

Living together: The Hawaiian Bobtail Squid – Vibrio fischeri Association