Bacteria; Proteobacteria; Gammaproteobacteria; Vibrionales; Vibrionaceae
Description and Significance
Originally named "Einheimischer Leuchtbacillus" by Bernard Fischer in 1888, Aliivibrio fischeri is a rod-shaped, bio-luminescent bacteria that can be found in marine environments. While free-floating, A. fischeri appears as a flagellate; however, once in symbiosis with other organisms, the flagella is lost.
A. fischeri plays a vital role in the development of the Hawaiian Bobtail squid in a mutualistic symbiosis in which the squid gains bioluminescence and protection from colonization of harmful organisms and A. fischeri gains a host and resources. Interestingly enough,the relationship between A. fischeri and the Bobtail squid is so exclusive that if A. fischeri is not present at birth, no other bacteria can colonize the light organ of the squid.
Additionally, A. fischeri has been used as a potential biosensor for heavy metal detection, in which A. fischeri has levels of detection as low as 6.4 μg/L (Futra 2014).
A. fischeri represents one of the first members of Vibrio to have its genome sequenced after the few pathogenic species within the genus. Like its counterparts, A. fischeri has two circular chromosomes and a 45.8-kbp plasmid. Chromosome I is significantly larger than Chromosome II (2.9 Mbp and 1.3 Mbp, respectively) and contains 11 of 12 rRNA operons.
A notable feature of the a A. fischeri genome is that it has the lowest G+C content of all species within Vibrionaceae at 38.3% and a nearly "4-fold greater percentage of unique genes on Chr II of" A. fischeri (Ruby et al. 2005). Additionally, A. fischeri's genome contains homologs of genes known to have toxic activity in pathogenic species of Vibrionaceae such as a CTX, ace, RTX, and zot, although the role of these genes and their influence on the bacterias' symbioses is unknown (Ruby et al, 2005)
Cell Structure, Metabolism and Life Cycle
A. fischeri is a facultative anaerobe, though it's lifestyle is largely anaerobic. It is thought that in the beginning phases of colonization, oxygen is plentiful and declines as the relationship matures (Dunn 2012).
A. fischeri utilizes glycerophospholipids, provided by the squid host, for anaerobic respiration with the terminal electron receptor being nitrate during the day. Nocturnally, glycerophospholipids are replaced with chitin for fermentation; however, chitin is only provided in hosts of at least 4 weeks in age (Thompson et al, 2017).
Ecology and Pathogenesis
A. fischeri can be found within temperate and subtropical marine environments as free-living saprophytic bacteria or within a host as a symbiont (Koropatnick, 2006).
While symbioses can occur with various species of marine fish and squids, A. fischeri is most notable for its relationship with the Hawaiian Bobtail squid, Euprymna scolopes in which the bacteria's bioluminescent properties can be observed. Once the population of A. fischeri has successfully colonized the light organ, the bacteria produce a "flavin reductase enzyme [that] catalyzes the oxidation of reduced [NAD(P)H] to NAD(P)," which causes the reduction of FMN (Futra et al, 2014). Subsequently, luciferase aids in the oxidation of the reduced FMN, producing a light quantum. This ability also lead to the discovery of quorum sensing, a process by which fluctuations in population size regulate gene expression.
A. fischeri , while related to few pathogenic species, is not known to be pathogenic in any case.
[Dunn, Anne. (2012). Vibrio fischeri Metabolism: Symbiosis and Beyond. Advances in microbial physiology. 61. 37-68. 10.1016/B978-0-12-394423-8.00002-0.
Evans, K. (2016). Better Know a Microbe: Aliivibrio fischeri. LabRoots. https://www.labroots.com/trending/microbiology/2537/microbe-aliivibrio-fischeri
Futra, D., Heng, L. Y., Surif, S., Ahmad, A., & Ling, T. L. (2014). Microencapsulated Aliivibrio fischeri in alginate microspheres for monitoring heavy metal toxicity in environmental waters. Sensors (Basel, Switzerland), 14(12), 23248–23268. https://doi.org/10.3390/s141223248
Koropatnick, T. (2006). The Squid-Vibrio Symbiosis. Microbial Life. https://serc.carleton.edu/microbelife/topics/marinesymbiosis/squid-vibrio/index.html
Thompson, L. R., Nikolakakis, K., Pan, S., Reed, J., Knight, R., & Ruby, E. G. (2017). Transcriptional characterization of Vibrio fischeri during colonization of juvenile Euprymna scolopes. Environmental microbiology, 19(5), 1845–1856. https://doi.org/10.1111/1462-2920.13684
Ruby, E. G., Urbanowski, M., Campbell, J., Dunn, A., Faini, M., Gunsalus, R., Lostroh, P., Lupp, C., McCann, J., Millikan, D., Schaefer, A., Stabb, E., Stevens, A., Visick, K., Whistler, C., & Greenberg, E. P. (2005). Complete genome sequence of Vibrio fischeri: a symbiotic bacterium with pathogenic congeners. Proceedings of the National Academy of Sciences of the United States of America, 102(8), 3004–3009. https://doi.org/10.1073/pnas.0409900102]
Page authored by Alexandria Reyes, student of Prof. Jay Lennon at IndianaUniversity.