The Mystery of Reproduction

Can you think of an organism that has been around for hundreds of years yet still very little is known about its life cycle? One such organism as this is Vibrio salmonicida. With the genus being Vibrio, you would think that it has a similar life history and reproduction to other species within that genus. However, the reproduction of Vibrio salmoncidia can be very different when the organism is in the water, as opposed to when it is in the host.

When the organism is in the water, it needs to be able to survive for a long time without supplemental nutrients (Hoff 1989). During this period of time, not much is happening in the cell. When the organism is in the water for a long period of time and needs to survive, it goes into a stage called starvation survival (Hoff 1989).  Since the nutritients in the sea water are very limited, the organism is unable to do anything. Therefore, Vibrio Salmonicida ceases growing during this period in the water (Hoff 1989).

Vibrio salmonicida’s supply of nutrients can be taken up from the water in order to survive until it reaches a host cell, where it will receive more nutrients in order to replicate and take over the host. However, it has been found that salinity and temperature do play an important role in Vibrio salmonicida’s survival. Kjell Arne Hoff’s research investigates how the salinity of the water affects Vibrio salmonicida, while keeping the temperature constant. The results showed that as the salt concentration increased in the water, the short-term starvation of Vibrio salmonicida decreased as the weeks increase (Hoff 1989). Therefore, the saltier the water, the harder it is for the bacteria to survive for a long time. This can greatly affect the areas in which Vibrio salmonicida live.

Unlike the well-documented life cycle of Vibrio salmoncida when it is in the water, there is not a lot of information about the bacteria when it is inside the host.  What is known about the life cycle, however, is the fact that the bacteria is transmitted through the fish population and is spread to the fish’s gut and other areas. The source of the bacteria is either from the water or from a wild fish (Bruno 1996). Vibrio salmonicida enters its selected fish via an unknown process, which likely involves the fish’s gills (Bjelland et al. 2012 a). The fish's bloodstream is an adequate place for nutrition acquisition. After the bacteria quickly goes through the bloodstream, it enters organs in the abdomen, which has more nutrients (Farmer III and Hickman-Brenner, 1991).

Once the organism enters the bloodstream, it uses one of its many flagella to find its way to the abdominal organs where the life cycle begins (Veterinary Science). The flagella allow the organism to move throughout the inside of the fish and spread the infection (Bjelland et al. 2012 a). Interestingly, if Vibrio salmonicida contains a gene known as LitR mutant, the bacterium has increased motility, adhesion, cell-to-cell adhesion, and biofilm formation (Bjelland et al. 2012 a). Therefore, the likelihood of the fish obtaining the disease is increased. Vibrio salmoncidia has a surface antigen VS-P1 that is released during the growth of the fish. However, not much is known about this; it is hypothesized that this antigen binds to particular antibodies to protect the bacteria from being engulfed by the fish’s immune system (Bjelland et al. 2012 a).

This is the final step in acquiring nutrients and creating a disease. Research supports that the bacteria releases a substance that is used to converse with other bacteria in the fish to make sure a deadly infection occurs (Veterinary Science). As stated earlier this infection occurs in the abdomen of the fish and can become extremely harmful, resulting in many different symptoms that will eventually lead to death.

Unfortunately, since the research in the life cycle of Vibrio salmonicida is lacking, it is hard to give an accurate picture of the life cycle. As of now this is the best information known about the organism.

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