Abstract
Gram-negative bacteria are known to subvert eukaryotic cell physiological mechanisms using a wide array of virulence factors, among which the type three-secretion system (T3SS) is often one of the most important. The T3SS constitutes a needle-like apparatus that the bacterium uses to inject a diverse set of effector proteins directly into the cytoplasm of the host cells where they can hamper the host cellular machinery for a variety of purposes. While the structure of the T3SS is somewhat conserved and well described, effector proteins are much more diverse and specific for each pathogen. The T3SS can remodel the cytoskeleton integrity to promote intracellular invasion, as well as silence specific eukaryotic cell signals, notably to hinder or elude the immune response and cause apoptosis. This is also the case in aquatic bacterial pathogens where the T3SS can often play a central role in the establishment of disease, although it remains understudied in several species of important fish pathogens, notably in Yersinia ruckeri. In the present review, we summarise what is known of the T3SS, with a special focus on aquatic pathogens and suggest some possible avenues for research including the potential to target the T3SS for the development of new anti-virulence drugs.
Highlights
2 The type 3 secretion system (T3SS)2.1 Structure of the Type III secretion system 2.2 Chaperones of the T3SS 2.3 Roles of the T3SS2.3.1 Effects of the T3SS on host cell signalling 2.3.2 Cytotoxic effects 2.3.3 Other means of circumventing the immune response2.3.4 Interference with the cytoskeleton to promote internalisation and cell invasion3 T3SS in aquatic pathogens 3.1 Edwardsiella spp. 3.2 Vibrio spp. 3.3 Aeromonas spp. 3.4 Flavobacterium spp. 3.5 Yersinia ruckeri 3.6 Pseudomonas spp.Rahmatelahi et al Veterinary Research (2021) 52:146
In gram-negative species, this envelope is formed of three layers: the inner-membrane which is composed of a phospholipid bilayer, a thin peptidoglycan cell wall composed of repeating units of N-acetyl glucosamine and N-actyl muramic acid and an outer-membrane, a feature unique to gram-negative bacteria, composed of phospholipids and lipopolysaccharides [7]
Since most of the research regarding the T3SS was conducted on pathogens of land animals, the present review will start with an overview of what is generally known about these T3SS, first in term of structure and regarding their functions and effector proteins
Summary
The demand for fish products has been increasing worldwide for multiple decades and with the output of fisheries largely stagnant, this demand has been mostly answered through the growth of aquaculture, in developing countries [1]. Bacterial pathogens have been associated with several outbreaks and much of the bacterial species involved belong to the group of the gram negative, with several known to harbor a T3SS that is often required for the establishment of infections. Since most of the research regarding the T3SS was conducted on pathogens of land animals, the present review will start with an overview of what is generally known about these T3SS, first in term of structure and regarding their functions and effector proteins It will focus on what has been discovered about the role of the T3SS in the establishment of diseases in aquatic organisms
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