Temperature-dependent expression of virulence genes in fish-pathogenic bacteria.
Bottom Line: A key factor in this expression is temperature.This is an interesting issue and progress needs to be made in order to diminish the economic losses caused by these diseases.The intention of this review is, for the first time, to compile the scattered results existing in the field in order to lay the groundwork for future research.
Virulence gene expression in pathogenic bacteria is modulated by environmental parameters. A key factor in this expression is temperature. Its effect on virulence gene expression in bacteria infecting warm-blooded hosts is well documented. Transcription of virulence genes in these bacteria is induced upon a shift from low environmental to a higher host temperature (37°C). Interestingly, host temperatures usually correspond to the optimum for growth of these pathogenic bacteria. On the contrary, in ectothermic hosts such as fish, molluscs, and amphibians, infection processes generally occur at a temperature lower than that for the optimal growth of the bacteria. Therefore, regulation of virulence gene expression in response to temperature shift has to be modulated in a different way to that which is found in bacteria infecting warm-blooded hosts. The current understanding of virulence gene expression and its regulation in response to temperature in fish-pathogenic bacteria is limited, but constant extension of our knowledge base is essential to enable a rational approach to the problem of the bacterial fish diseases affecting the aquaculture industry. This is an interesting issue and progress needs to be made in order to diminish the economic losses caused by these diseases. The intention of this review is, for the first time, to compile the scattered results existing in the field in order to lay the groundwork for future research. This article is an overview of those relevant virulence genes that are expressed at temperatures lower than that for optimal bacterial growth in different fish-pathogenic bacteria as well as the principal mechanisms that could be involved in their regulation.
No MeSH data available.
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Mentions: Disease development in fish is a complex process involving the interaction of a susceptible host, a virulent microorganism, and environmental factors. It is clear that in the aquaculture industry the third requirement is particularly important since the high densities and stress to which fish are commonly subjected favor the appearance of diseases that are infrequent or even non-existent in natural environments (Figure 1). A key environmental stress factor in outbreaks of most fish bacterial diseases in fish farms is water temperature. In some cases, outbreaks occur when water temperature drops to a certain value: Cold water vibriosis, (Enger et al., 1991); Cold water disease (Cipriano and Holt, 2005); Redmouth disease (Fernandez et al., 2007a). In others, such as: Lactococcosis (Vendrell et al., 2006), Haemorrhagic septicaemia (Austin and Austin, 2007), and Edwardsiellosis (Mohanty and Sahoo, 2007) outbreaks are related to an increase in water temperature. Interestingly, a remarkable number of bacterial diseases in aquaculture, particularly those of freshwater, occurred at temperatures below that of the optimal growth (TBO) of the infecting bacteria considering the optimum growth temperature for a particular bacterium to be that at which the fastest growth rate was observed under laboratory conditions. This temperature is usually higher than those found in the aquatic environment where the bacteria live or within their ectothermic hosts. Therefore, virulence gene expression in these bacteria should be regulated in such a way that maximum expression must occur at TBO. Nevertheless, since the body temperature of ectothermic animals is very close to the environmental temperature, additional factors must be necessary for full virulence, such as a co-regulation interaction between temperature and host metabolic processes.
No MeSH data available.