Adapting To An Extreme Environment

Vibrio salmonicida is very intriguing for a bacterium. From the way they infect their hosts, to how they travel from host to host, this species has many functional adaptations. Vibrio salmonicida is a bacterium found only in marine environments. It is Gram-negative and rod-shaped. Interestingly, it is motile and can have up to nine polar flagella (Bjelland et al. 2012 b). The flagella play a vital role in the success and transmission of Cold-water Vibrosis. Studies indicate that in order to be transmitted from host to host, Vibrio salmonicida must have functioning flagella. The main function of the flagella is to transport the bacteria into an environment that it can rapidly multiply in. Interestingly, once the host is infected, flagella increases the rate of disease spread. However, flagella is not necessary for infection to lead to death of the host. In some cases the presence of it can actually decrease infection because the flagella is a common site for the fishes immune system to attack the bacteria (Bjelland et al. 2012 b).

Another very important and interesting adaptation is Vibrio salmonicida’s ability to monitor the density of itself in the blood of its host and then regulate its production to ensure fatal infection (Bjelland et al. 2012 b). This phenomenon is referred to as "quorum sensing" and is seen in many other organisms as well. Quorum sensing in Vibrio salmonicida affects the LitR gene and its expression and link to infection. LitR is a gene that is thought to increase the production of this bacterium. When the bacteria cell density is high enough, the mRNA for LitR is thought to be stabilized, causing LitR to be produced and thus more bacteria produced as well (Bjelland et al. 2012 b). Research has shown that cells with a negative LitR mutation have decreased host mortality rates. This same study showed that virulence increased at higher salt concentrations and warmer temperatures (Bjelland et al. 2012 b).

The three closest relatives of Vibrio salmonicida are Vibrio fischeri, Vibrio logei, and Vibrio wodanis, and these all show bioluminescent characteristics in natural habitats. Studies have shown that although Vibrio salmonicida does not show these properties in nature, they do have the genes to do so, and under certain conditions within a lab can be bioluminescent (Fidopiastis 1998). Though Vibrio salmonicida can be bioluminescent, it is not necessary for its life cycle (Bjelland et al. 2012 b).

It is obvious that Vibrio salmonicida has made several adaptations for its environment. Interestingly, this is the only environment that this bacteria is found in. Without a high salinity and low temperature, Vibrio salmonicida does not survive. To this date it is unknown exactly how Vibrio salmonicida functions in regards to its ability to survive in this extreme environment and how it infects its host. Much research is being conducted within these topics because of the interesting nature of this bacteria.

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