Amyloid-Like Adhesins Produced by Floc-Forming and Filamentous Bacteria in Activated Sludge

Abstract

Amyloid proteins (fimbriae or other microbial surface-associated structures) are expressed by many types of bacteria, not yet identified, in biofilms from various habitats, where they likely are of key importance to biofilm formation and biofilm properties. As these amyloids are potentially of great importance to the floc properties in activated sludge wastewater treatment plants (WWTP), the abundance of amyloid adhesins in activated sludge flocs from different WWTP and the identity of bacteria producing these were investigated. Amyloid adhesins were quantified using a combination of conformationally specific antibodies targeting amyloid fibrils, propidium iodide to target all fixed bacterial cells, confocal laser scanning microscopy, and digital image analysis. The biovolume fraction containing amyloid adhesins ranged from 10 to 40% in activated sludge from 10 different WWTP. The identity of bacteria producing amyloid adhesins was determined using fluorescence in situ hybridization with oligonucleotide probes in combination with antibodies or thioflavin T staining. Among the microcolony-forming bacteria, amyloids were primarily detected among Alpha-and Betaproteobacteria and Actinobacteria. A more detailed analysis revealed that many denitrifiers (from Thauera, Azoarcus, Zoogloea, and Aquaspirillum-related organisms) and Actinobacteria-related polyphosphate-accumulating organisms most likely produced amyloid adhesins, whereas nitrifiers did not. Many filamentous bacteria also expressed amyloid adhesins, including several Alphaproteobacteria (e.g., Meganema perideroedes), some Betaproteobacteria (e.g., Aquaspirillum-related filaments), Gammaproteobacteria (Thiothrix), Bacteroidetes, Chloroflexi (e.g., Eikelboom type 1851), and some foam-forming Actinobacteria (e.g., Gordonia amarae). The results show that amyloid adhesins were an abundant component of activated sludge extracellular polymeric substances and seem to have unexpected, divers functions.

Microbial Amyloids Induce Interleukin 17A (IL-17A) and IL-22 Responses via Toll-Like Receptor 2 Activation in the Intestinal Mucosa

“…Thus, the IL-17A production that we observed by CD4 ϩ and CD8 ϩ T cells in vivo at 48 h was most likely due to memory responses generated by immune cells during previous bacterial or amyloid encounters. Despite the fact that curli are produced only by a number of commensal and pathogenic enteric bacteria, amyloids are present in biofilms of representatives from the phyla Bacteroidetes and Firmicutes, which dominate the microbiota of the gastrointestinal tract (13,18,41,44,45,64). Moreover, expression of various serum amyloid A (SAA) proteins in the gastrointestinal tract has been demonstrated (38).…”

Epithelial Cells Augment Barrier Function via Activation of the Toll-Like Receptor 2/Phosphatidylinositol 3-Kinase Pathway upon Recognition of Salmonella enterica Serovar Typhimurium Curli Fibrils in the Gut

“…Bacterial species express amyloid fibrils as a major component of their extracellular matrix in biofilms. In addition to members of the Proteobacteria, members of two of the major bacterial phyla to which most intestinal commensals belong, Bacteroidetes and Firmicutes, have been reported to express bacterial amyloids as a component of their biofilms (39,41,43,44,82,83). Since amyloids are common across several bacterial phyla and have a highly conserved quaternary structure, amyloid fibrils may serve as targets for immune surveillance by giving the immune system an opportunity to detect the presence of many microorganisms by recognizing one conserved molecule expressed by all.…”

Programmable biofilm-based materials from engineered curli nanofibres

“…Similar amyloid nanofibres have been shown to have a strength comparable to steel and a mechanical stiffness comparable to silk 10 , suggesting that biofilms with high amyloid content would be able to withstand mechanically demanding environments. Third, functional amyloid fibrils are abundant in many naturally occurring bacterial biofilms and can constitute up to 10-40% of the total biovolume of a biofilm 11 , indicating that curli can be artificially engineered to comprise a significant portion of the biofilm. In addition, although analogous extracellular functional amyloids are produced by many bacteria, the curli system is currently the best studied and is native to the canonical model bacterium E. coli, making it an attractive starting platform for the development of engineered materials.…”