Curli Extracellular Matrix - The Functional Fold: Amyloid Structures in Nature - page 124

Being amyloidogenic, curli proteins offer fast and efficient
assembly as well as a degradation resistant coat. Curli are a critical
component for the biofilm architecture, and further promote multi-
cellular aggregation and pellicle formation, by mediating cell-cell
interaction within a colony, which is important to produce the
characteristic thick biofilm.

22,39-42

The curli matrix layer confers the bacteria with protection and
enhanced survival outside on the host one hand, and persistence
and virulence tools within the host on the other hand. Indeed,

Enterobacteriaceae may spend long periods of their life cycle outside

animal or plant hosts, where they may encounter suboptimal and
stressful conditions. One way to deal with these changes is to attach
to solid surfaces in an aqueous environment and form biofilm, in this
way maximizing metabolic breakdown and stress management.

43

Accordingly, curli amyloids were shown to assist bacteria to attach
to abiotic inert surfaces, including non-hydrophobic ones.

44,45

Among the amyloid-facilitated binding surfaces are glass, stainless
steel, polystyrene, and Teflon.

22,45,46

Furthermore, curli expression
was demonstrated to be protective against a range of antimicrobial
agents, such as hydrogen peroxidase, quaternary ammonium,
chlorine, and to grant enhanced survival during desiccation in the
absence of nutrients.

46-48

This facilitates bacterial colonization and
persistence in medical and technical devises, leading to infections and
biodeterioration. For example, bacterium

found in biofilms that have developed on catheters introduced into
the urinary tract.

E . coli is the most common

49
Within the host, where nutritional resources are readily
available, bacteria use biofilm to persist and further disseminate
throughout the host. In this environment, either animal or plant, curli
fibres function to promote stable adhesion to various tissues.

50-52

Hence, curli have a major role in bacterial pathogenicity. A list of
evidence supports the importance of curli during the infectious
process. Curli are expressed at 37°C in biofilms of many clinical
isolates.

Among clinical isolates, curli are expressed by most
enterohaemorrhagic, enterotoxigenic, and sepsis strains, whereas
enteroinvasive and enteropathogenic strains do not express curli.

41

18,53

Curli was demonstrated to interact with a variety of host proteins,
many of which are proposed to facilitate bacterial dissemination
through the host. For instance, curli binding to extracellular matrix
and contact-phase proteins (such as laminin, fibrinogen, bradykinin,