Expression Of Virulence Genes In Bacteria Research Articles

Regulation of Virulence Gene Expression in Bacteria: A Review

Bacterial diseases are the leading cause of death worldwide through the involvement of virulence determinants. Virulence genes encode virulence factors which are essential for pathogenesis and infectious disease development in bacteria. The virulence factor concept helps for further investigations in the fields of microbial pathogenesis. The objective of this paper is to review regulation of virulence gene expression in bacteria. Virulence genes can be acquired via spontaneous mutations or through horizontal gene transfer mechanisms. Bacteria sense and respond to environmental stimuli in the host during infection. Successful host infection can be possible by coordinated expression of multitude of virulence genes. They adapt in the host by modulating its gene expression. Pathogenic bacteria possess many regulatory networks that control the production of virulence factors which enable the bacteria to survive and proliferate in the host. The most common forms of regulation of genome expression are by involvement of transcription factors, post-transcriptional modifications, ribo-regulation, environmental flux sensing, stress response and biofilm formation through quorum sensing. Virulence gene expression is carefully controlled to ensure correct spatiotemporal production of virulence factors. Regulation of virulence gene expression is very complex and influenced by environmental factors. Major regulatory control mechanisms used by pathogenic bacteria are alternative sigma factors and the two component regulatory systems. They do not always express virulence factors because it is energetically costly and reduces bacterial fitness. Therefore, they need to regulate their virulence properly in order to maximize their fitness and it is a key invasion strategy of pathogens. Keywords: Bacteria, Expression, Regulation, Virulence gene DOI: 10.7176/JBAH/11-3-02 Publication date: February 28 th 2021

Temperature-dependent expression of virulence genes in fish-pathogenic bacteria.

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.