Promiscuous cross-seeding between bacterial amyloids promotes interspecies biofilms

Area of Science:

• Microbiology
• Biochemistry
• Structural Biology

Background:

• Amyloids are protein aggregates linked to neurodegenerative diseases, with typically high seeding specificity.
• Bacterial functional amyloids, such as curli, play roles in microbial adhesion and biofilm formation.
• Curli fibers are composed of CsgA subunits templated by CsgB nucleators.

Purpose of the Study:

• To investigate the cross-seeding potential of bacterial functional amyloids (curli).
• To determine if curli homologs from different bacterial species can cross-seed.
• To assess the impact of curli cross-seeding on interspecies biofilm development.

Main Methods:

• In vitro cross-seeding assays using purified curli subunits from various Gram-negative bacteria.
• Analysis of polymerization acceleration by homologous and heterologous curli fibers.
• Construction and observation of mixed-colony biofilms involving different bacterial species.

Main Results:

• Curli subunit homologs from Escherichia coli, Salmonella typhimurium, and Citrobacter koseri demonstrated in vitro cross-seeding.
• Escherichia coli CsgA polymerization was accelerated by curli fibers from Shewanella oneidensis, despite low sequence identity.
• Interspecies curli assembly in mixed biofilms enhanced bacterial attachment and pellicle formation.

Conclusions:

• Curli functional amyloids exhibit relaxed seeding specificity compared to disease-associated amyloids.
• Heterogeneous curli fiber assembly facilitates multispecies biofilm development.
• This cross-seeding ability may be crucial for bacterial community structure and function.