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Dickeya solani is a pectinolytic bacterium that causes significant losses of potato crops. Interaction between bacteria and plant during infection and transmission within the host tissue are associated with a variety of challenges, including exposure to physico-chemical factors that induce osmotic, acidic, oxidative or thermal stresses. In this work, we tested the effects of various potentially adverse conditions on growth and fitness of the D. solani IPO2222 type strain. We found the bacteria were able to withstand a great variety of stressful conditions. Treatment with high concentrations of osmolytes (up to 1.6 Osm), low pH (5.0), or elevated temperature (up to 40 °C) was still tolerated. Short term exposure to these conditions did not impair the ability of bacteria to macerate potato tuber tissue. However, D. solani was sensitive to a relatively low content (above 0.5 mM) of the oxidant H2O2 and treatment with this oxidant caused a loss of culturability. All used stressful conditions are known to affect the stability, and structure of proteins and induction of the folding stress-related genes, dnaK, dnaJ and groEL, was observed in most cases. The only exception was oxidative stress for which the chaperone genes were slightly down-regulated. This observation is in line with a low tolerance of D. solani to H2O2.

A pathogenic lifestyle is inextricably linked with the constant necessity of facing various challenges exerted by the external environment (both within and outside the host). To successfully colonize the host and establish infection, pathogens have evolved sophisticated systems to combat the host defense mechanisms and also to be able to withstand adverse environmental conditions. Proteases, as crucial components of these systems, are involved in a variety of processes associated with infection. In phytopathogenic bacteria, they play important regulatory roles and modulate the expression and functioning of various virulence factors. Secretory proteases directly help avoid recognition by the plant immune systems, and contribute to the deactivation of the defense response pathways. Finally, proteases are important components of protein quality control systems, and thus enable maintaining homeostasis in stressed bacterial cells. In this review, we discuss the known protease functions and protease-regulated signaling processes associated with virulence of plant pathogenic bacteria.

Background An increasing resistance of bacteria to the commonly used antimicrobials forces to search for alternative or supportive ways to cure infections. Targeting virulence factors is one of such approaches. The bacterial HtrA proteins are strongly involved in virulence and the lack of functional HtrA in many cases impairs invasiveness of pathogens. HtrAs act by protecting the cells under stressful conditions as well as they take direct part in invasion of the host. The latter function is played predominantly by the recently identified extracellular fraction of HtrA. This review aims to evaluate HtrAs as therapeutic targets, including design of chemical inhibitors and vaccines. Methods We undertook a thorough search of bibliographic databases for peer-reviewed scientific literature. Results One hundred and sixty-four papers were included in the review. First, we briefly summarized key structural and functional properties of known HtrA proteins with the special focus on the extracellular HtrA fraction. Then we provided an overview of efforts and advancements to target HtrAs of pathogenic bacteria as a promising antimicrobial therapy. In some cases, encouraging results were obtained and application of HtrAspecific inhibitors protected tissues from damage and killed bacteria. Also promising reports concerning the use of HtrA as a protective antigen in several disease models have recently been published. Conclusion The findings of this review suggest that the exported HtrA proteins are very attractive therapeutic targets due to their accessibility, significance in virulence and immunogenicity. However, further extensive studies are still needed to develop a safe antimicrobial treatment.