Biology Reference
In-Depth Information
BASICS
This section presents the conceptual basics of the interdisciplinary subject. First of all, the quorum
sensing system of the organism
Aliivibrio salmonicida
is described. The section gives an insight into the
initial question of the dynamic biological system and the underlying research project. In the following,
a Petri net definition is given. Special consideration is given to the Petri net language as it serves as the
simulation technique for the quorum sensing system.
Quorum sensing
Over time, natural science and its studies on living organisms has answered many essential questions.
But still, a lot of biochemical processes are far beyond our understanding. Research groups around the
world address their attention to unanswered questions and biological phenomena. One question that
is not answered yet is how the biological system
quorum sensing
works in detail. Understanding the
intracellular molecular machinery that is responsible for the complex collective behavior of cellular and
multicellular populations is one of the main tasks in natural science.
Quorum sensing is a sophisticated cell-to-cell signaling system and an important issue in the study
of bacterial behavior dynamics. The intracellular circuitry of signal transduction and gene expression
has become the focus of important research activities. Many bacterial species use quorum sensing
to coordinate their gene expression according to the local density of their population. The bacteria
population benefits from quorum sensing as they have the ability to restrict certain behavioral traits. By
this process, the system allows to control the gene expression of the entire bacteria community and to
have an effect on the bacterial behavior [Schauder
et al.
, 2001]. Accordingly, bacteria populations are
able to control and limit activities that will not have any impact on small population densities.
In the aspect of fish infection by pathogenic bacteria, the exploration of the quorum sensing network
is very important. The quorum sensing regulated virulence factor production is of great importance in
the development of more efficient vaccines and vaccination strategies and is of broad interest to a large
scientific community.
Vibrio
infection which occurs in many species including shellfish, fish and humans,
has been reported throughout the world. Fish infection with
Vibrio
bacteria is one of the major bacterial
threats in marine aquaculture [Enger
et al.
, 1989]. Breading at high densities under artificial conditions
imposes considerable risks of losses from outbreaks of infectious diseases. Therapeutic treatments
may harm the environment, and modern intensive farming practices are increasingly confronted with
husbandry diseases. Intensive fish farming has unfortunately suffered from disease problems although
effective vaccines have reduced the economical losses dramatically. Farming of other marine species
(cod, turbot, halibut etc.) has, however, faced other disease problems, which require new vaccines,
vaccination strategies or use of alternative therapeutics, individually adjusted depending on the fish
pathogen and its host.
Motivated by the goal of having a better understanding of
Vibrio
infections we began to examine the
quorum sensing network of the organism
Aliivibrio salmonicida
.
Aliivibrio salmonicida
, a moderate
halophilic and psychrophilic bacterium, is the causative agent of cold-water vibriosis. In contrast to other
bacterial infections in fish, which usually occur during summer months, outbreaks of cold-water vibriosis
occur predominantly during winter months when water temperatures are below 10
◦
. Surprisingly, no
exotoxins or enzymes with cytolytic activity have been identified in
Aliivibrio salmonicida
, although the
infection results in tissue degradation, haemolysis and sepsis
in vivo
[Totland
et al.
, 1988]. Infections
due to
Aliivibrio salmonicida
have a 50-fold greater occurrence in salmon compared to cod, suggesting
that this pathogen requires very specific host properties [Schrøder
et al.
, 1992].
The whole genome
