Widespread abundance of functional bacterial amyloid in mycolata and other gram-positive bacteria

Chaperones mainly suppress primary nucleation during formation of functional amyloid required for bacterial biofilm formation

Unlike misfolding in neurodegenerative diseases, aggregation of functional amyloids involved in bacterial biofilm, e.g. CsgA (E. coli) and FapC (Pseudomonas), is carefully regulated.

Solid-State NMR Investigations of Extracellular Matrixes and Cell Walls of Algae, Bacteria, Fungi, and Plants

Extracellular matrixes (ECMs), such as the cell walls and biofilms, are important for supporting cell integrity and function and regulating intercellular communication. These biomaterials are also of significant interest to the production of biofuels and the development of antimicrobial treatment. Solid-state nuclear magnetic resonance (ssNMR) and magic-angle spinning-dynamic nuclear polarization (MAS-DNP) are uniquely powerful for understanding the conformational structure, dynamical characteristics, and supramolecular assemblies of carbohydrates and other biomolecules in ECMs. This review highlights the recent high-resolution investigations of intact ECMs and native cells in many organisms spanning across plants, bacteria, fungi, and algae. We spotlight the structural principles identified in ECMs, discuss the current technical limitation and underexplored biochemical topics, and point out the promising opportunities enabled by the recent advances of the rapidly evolving ssNMR technology.

Folding Steps in the Fibrillation of Functional Amyloid: Denaturant Sensitivity Reveals Common Features in Nucleation and Elongation

Functional bacterial amyloids (FuBA) are intrinsically disordered proteins (IDPs) which rapidly and efficiently aggregate, forming extremely stable fibrils. The conversion from IDP to amyloid is evolutionarily optimized and likely couples folding to association. Many FuBA contain several imperfect repeat sequences which contribute to the stability of mature FuBA fibrils. Aggregation can be considered an intermolecular extension of the process of intramolecular protein folding which has traditionally been studied using chemical denaturants. Here we employ denaturants to investigate folding steps during fibrillation of CsgA and FapC. We quantify protein compactification (i.e. the extent of burial of otherwise exposed surface area upon association of proteins) during different stages of fibrillation based on the dependence of fibrillation rate constants on the denaturant concentration (m-values) determined from fibrillation curves. For both proteins, urea mainly affects nucleation and elongation (not fragmentation), consistent with the fact that these steps involve both intra- and intermolecular association. The two steps have similar m-values, indicating that activation steps in nucleation and elongation involve the same level of folding. Surprisingly, deletion of two or three repeats from FapC leads to larger m-values (i.e. higher compactification) during the activation step of fibril growth. This observation is extended by SAXS analysis of the fibrils which indicates that weakening of the amyloidogenic core caused by repeat deletions causes a larger portion of normally unstructured regions of the protein to be included into the amyloid backbone. We conclude that the sensitivity of fibrillation to denaturants can provide useful insight into molecular mechanisms of aggregation.

Does Alzheimer's disease stem in the gastrointestinal system?

Over the last decades, our knowledge of the key pathogenic mechanisms of Alzheimer's disease (AD) has dramatically improved. Regarding the limitation of current therapeutic strategies for the treatment of multifactorial diseases, such as AD, to be translated into the clinic, there is a growing trend in research to identify risk factors associated with the onset and progression of AD. Here, we review the current literature with a focus on the relationship between gastrointestinal (GI)/liver diseases during the lifespan and the incidence of AD, and discuss the possible mechanisms underlying the link between the diseases. We also aim to review studies evaluating the possible link between the chronic use of the most common GI medications and the future risk of AD development.

Nanotargeting of Resistant Infections with a Special Emphasis on the Biofilm Landscape

Bacterial resistance to antimicrobial compounds is a growing concern in medical and public health circles. Overcoming the adaptable and duplicative resistance mechanisms of bacteria requires chemistry-based approaches. Engineered nanoparticles (NPs) now offer unique advantages toward this effort. However, most in situ infections (in humans) occur as attached biofilms enveloped in a protective surrounding matrix of extracellular polymers, where survival of microbial cells is enhanced. This presents special considerations in the design and deployment of antimicrobials. Here, we review recent efforts to combat resistant bacterial strains using NPs and, then, explore how NP surfaces may be specifically engineered to enhance the potency and delivery of antimicrobial compounds. Special NP-engineering challenges in the design of NPs must be overcome to penetrate the inherent protective barriers of the biofilm and to successfully deliver antimicrobials to bacterial cells. Future challenges are discussed in the development of new antibiotics and their mechanisms of action and targeted delivery via NPs.

Identification of amyloidogenic proteins in the microbiomes of a rat Parkinson's disease model and wild-type rats

Cross seeding between amyloidogenic proteins in the gut is receiving increasing attention as a possible mechanism for initiation or acceleration of amyloid formation by aggregation-prone proteins such as αSN, which is central in the development of Parkinson's disease (PD). This is particularly pertinent in view of the growing number of functional (i.e., benign and useful) amyloid proteins discovered in bacteria. Here we identify two amyloidogenic proteins, Pr12 and Pr17, in fecal matter from PD transgenic rats and their wild type counterparts, based on their stability against dissolution by formic acid (FA). Both proteins show robust aggregation into ThT-positive aggregates that contain higher-order β-sheets and have a fibrillar morphology, indicative of amyloid proteins. In addition, Pr17 aggregates formed in vitro showed significant resistance against FA, suggesting an ability to form highly stable amyloid. Treatment with proteinase K revealed a protected core of approx. 9 kDa. Neither Pr12 nor Pr17, however, affected αSN aggregation in vitro. Thus, amyloidogenicity does not per se lead to an ability to cross-seed fibrillation of αSN. Our results support the use of proteomics and FA to identify amyloidogenic protein in complex mixtures and suggests that there may be numerous functional amyloid proteins in microbiomes.

Challenges Associated With the Formation of Recombinant Protein Inclusion Bodies in Escherichia coli and Strategies to Address Them for Industrial Applications

Recombinant proteins are becoming increasingly important for industrial applications, where Escherichia coli is the most widely used bacterial host for their production. However, the formation of inclusion bodies is a frequently encountered challenge for producing soluble and functional recombinant proteins. To overcome this hurdle, different strategies have been developed through adjusting growth conditions, engineering host strains of E. coli, altering expression vectors, and modifying the proteins of interest. These approaches will be comprehensively highlighted with some of the new developments in this review. Additionally, the unique features of protein inclusion bodies, the mechanism and influencing factors of their formation, and their potential advantages will also be discussed.

Functional Amyloids

When protein/peptides aggregate, they usually form the amyloid state consisting of cross β-sheet structure built by repetitively stacked β-strands forming long fibrils. Amyloids are usually associated with disease including Alzheimer's. However, amyloid has many useful features. It efficiently transforms protein from the soluble to the insoluble state in an essentially two-state process, while its repetitive structure provides high stability and a robust prion-like replication mechanism. Accordingly, amyloid is used by nature in multifaceted and ingenious ways of life, ranging from bacteria and fungi to mammals. These include (1) Structure: Templating for small chemical molecules (Pmel17), biofilm formation in bacteria (curli), assisting aerial hyphae formation in streptomycetes (chaplins) or monolayer formation at a surface (hydrophobins). (2) Reservoirs: A storage state for peptide/proteins to protect them from their surroundings or vice versa (storage of peptide hormones in mammalian secretory granules or major basic protein in eosinophils). (3) Information carriers: The fungal immune system (HET-s prion in Podospora anserina, yeast prions) or long-term memory (e.g., mnemons in yeast, cytoplasmic polyadenylation element-binding protein in aplysia). Aggregation is also used to (4) "suppress" the function of the soluble protein (e.g., Cdc19 in yeast stress granules), or (5) "signaling" through formation of oligomers (e.g., HET-s prion, necroptosis-related proteins RIP1/RIP3). This review summarizes current knowledge on functional amyloids with a focus on the amyloid systems curli in bacteria, HET-s prion in P. anserina, and peptide hormone storage in mammals together with an attempt to highlight differences between functional and disease-associated amyloids.

Microbiota-gut-brain axis and toll-like receptors in Alzheimer's disease

Alzheimer’s disease (AD) is a multifactorial disease which involves both the periphery and central nervous system (CNS). It has been recently recognized that gut microbiota interacts with the gut and brain (microbiota-gut-brain axis), contributing to the pathogenesis of neurodegenerative diseases, such as AD. Dysbiosis of gut microbiota can induce increased intestinal permeability and systemic inflammation, which may lead to the development of AD pathologies and cognitive impairment via the neural, immune, endocrine, and metabolic pathways. Toll-like receptors (TLRs) play an important role in the innate immune system via recognizing microbes-derived pathogens and initiating the inflammatory process. TLRs have also been found in the brain, especially in the microglia, and have been indicated in the development of AD. In this review, we summarized the relationship between microbiota-gut-brain axis and AD, as well as the complex role of TLRs in AD. Intervention of the gut microbiota or modulation of TLRs properly might emerge as promising preventive and therapeutic strategies for AD.

Bacterial amphiphiles as amyloid inducers: Effect of Rhamnolipid and Lipopolysaccharide on FapC fibrillation

Pseudomonas species export the amyloid-forming protein FapC to strengthen bacterial biofilm. P. species also produce the biosurfactant rhamnolipid (Rhl) and its outer membrane contains lipopolysaccharide (LPS). Given the possible contacts between FapC, Rhl and LPS, we here investigate how Rhl and LPS affect FapC fibrillation compared with SDS, known to promote fibrillation of proteins at sub-micellar concentrations. Micelles of all three surfactants help FapC bypass the nucleation lag phase, leading to rapid fibrillation, which persists even at high concentrations of micelles and incorporates almost all available FapC monomers. Fibrils formed at high micellar concentrations of Rhl and SDS seed fibrillation at low surfactant concentrations while retaining the original fibril structure. FapC interacts strongly with SDS to form a dense network of narrow fibrils. Small angle X-ray scattering (SAXS) analyses reveal that surfactants reduce the population of intermediates in the fibrillation process and detect a fast aggregation step over the first 2-4 h which precedes the main fibrillation monitored by Thioflavin T. An additional SAXS-detected rearrangement of early aggregates occurs after 4-10 h. At high Rhl concentrations, the micelles are decorated with protein fibrils. SDS induces FapC fibrillation so efficiently that epigallocatechin-3-gallate (EGCG) is unable to inhibit this process. However, EGCG stimulates FapC oligomer formation and inhibits fibrillation both on its own and in the presence of Rhl and LPS. This oligomer could be modelled as a compact core with a flexible shell. This suggests that EGCG can override the natural amyloid-stimulatory properties of these biosurfactants and thus target biofilm.

Microbial functional amyloids serve diverse purposes for structure, adhesion and defence

The functional amyloid state of proteins has in recent years garnered much attention for its role in serving crucial and diverse biological roles. Amyloid is a protein fold characterised by fibrillar morphology, binding of the amyloid-specific dyes Thioflavin T and Congo Red, insolubility and underlying cross-β structure. Amyloids were initially characterised as an aberrant protein fold associated with mammalian disease. However, in the last two decades, functional amyloids have been described in almost all biological systems, from viruses, to bacteria and archaea, to humans. Understanding the structure and role of these amyloids elucidates novel and potentially ancient mechanisms of protein function throughout nature. Many of these microbial functional amyloids are utilised by pathogens for invasion and maintenance of infection. As such, they offer novel avenues for therapies. This review examines the structure and mechanism of known microbial functional amyloids, with a particular focus on the pathogenicity conferred by the production of these structures and the strategies utilised by microbes to interfere with host amyloid structures. The biological importance of microbial amyloid assemblies is highlighted by their ubiquity and diverse functionality.

Imperfect repeats in the functional amyloid protein FapC reduce the tendency to fragment during fibrillation

Functional amyloid (FA) is widespread in bacteria and serves multiple purposes such as strengthening of biofilm and contact with eukaryotic hosts. Unlike pathological amyloid, FA has been subjected to evolutionary optimization which is likely to be reflected in the aggregation mechanism. FA from different bacteria, including Escherichia coli (CsgA) and Pseudomonas (FapC), contains a number of imperfect repeats which may be key to efficient aggregation. Here we report on the aggregative behavior of FapC constructs which represent all single, double, and triple deletions of the protein's three imperfect repeats. Analysis of the fibrillation kinetics by the program Amylofit reveals that the removal of these repeats increases the tendency of the growing fibrils to fragment and also generally increases aggregation half-times. Remarkably, even the mutant lacking all three repeats was able to fibrillate, although fibrillation was much more irregular and led to significantly altered and destabilized fibrils. We conclude that imperfect repeats can promote fibrillation efficiency thanks to their modular design, though the context of the imperfect repeats also plays a significant role.

The Sheaths of Methanospirillum Are Made of a New Type of Amyloid Protein

The genera Methanospirillum and Methanosaeta contain species of anaerobic archaea that grow and divide within proteinaceous tubular sheaths that protect them from environmental stressors. The sheaths of Methanosaeta thermophila PT are composed of the 60.9 kDa major sheath protein MspA. In this study we show that sheaths purified from Methanospirillum hungatei JF-1 are regularly striated tubular structures with amyloid-like properties similar to those of M. thermophila PT. Depolymerizing the sheaths from M. hungatei JF-1 allowed us to identify a 40.6 kDa protein (WP_011449234.1) that shares 23% sequence similarity to MspA from M. thermophila PT (ABK14853.1), indicating that they might be distant homologs. The genome of M. hungatei JF-1 encodes six homologs of the identified MspA protein. Several homologs also exist in the related strains Methanospirillum stamsii Pt1 (7 homologs, 28–66% sequence identity), M. lacunae Ki8-1 C (15 homologs, 29–60% sequence identity) and Methanolinea tarda NOBI-1 (2 homologs, 31% sequence identity). The MspA protein discovered here could accordingly represent a more widely found sheath protein than the MspA from M. thermophila PT, which currently has no homologs in the NCBI Reference Sequence database (RefSeq).

Ecology and Biogenesis of Functional Amyloids in Pseudomonas

Functional amyloids can be found in the extracellular matrix produced by many bacteria during biofilm growth. They mediate the initial attachment of bacteria to surfaces and provide stability and functionality to mature biofilms. Efficient amyloid biogenesis requires a highly coordinated system of amyloid subunits, molecular chaperones and transport systems. The functional amyloid of Pseudomonas (Fap) represents such a system. Here, we review the phylogenetic diversification of the Fap system, its potential ecological role and the dedicated machinery required for Fap biogenesis, with a particular focus on the amyloid exporter FapF, the structure of which has been recently resolved. We also present a sequence covariance-based in silico model of the FapC fiber-forming subunit. Finally, we highlight key questions that remain unanswered and we believe deserve further attention by the scientific community.

The Gut-Brain Axis in Alzheimer's Disease and Omega-3. A Critical Overview of Clinical Trials

Despite intensive study, neurodegenerative diseases remain insufficiently understood, precluding rational design of therapeutic interventions that can reverse or even arrest the progressive loss of neurological function. In the last decade, several theories investigating the causes of neurodegenerative diseases have been formulated and a condition or risk factor that can contribute is described by the gut-brain axis hypothesis: stress, unbalanced diet, and drugs impact altering microbiota composition which contributes to dysbiosis. An altered gut microbiota may lead to a dysbiotic condition and to a subsequent increase in intestinal permeability, causing the so-called leaky-gut syndrome. Herein, in this review we report recent findings in clinical trials on the risk factor of the gut-brain axis in Alzheimer's disease and on the effect of omega-3 supplementation, in shifting gut microbiota balance towards an eubiosis status. Despite this promising effect, evidences reported in selected randomized clinical trials on the effect of omega-3 fatty acid on cognitive decline in Alzheimer's disease are few. Only Mild Cognitive Impairment, a prodromal state that could precede the progress to Alzheimer's disease could be affected by omega-3 FA supplementation. We report some of the critical issues which emerged from these studies. Randomized controlled trials in well-selected AD patients considering the critical points underlined in this review are warranted.

High-Quality Draft Genome Sequence of Sphaerisporangium cinnabarinum ATCC 31213

A high-quality draft genome sequence of Sphaerisporangium cinnabarinum ATCC 31213 is presented here. This bacterium produces several important bioactive compounds and may also produce functional amyloids. This is the first sequenced genome from the genus Sphaerisporangium , and it will be essential in determining the nature of the potential amyloid protein.

The Extracellular Polymeric Substances of Legionella pneumophila Biofilms Contain Amyloid Structures

Human infection by bacteria of the genus Legionella most often result in the pneumonia known as Legionnaires Disease. Legionella is found as a resident of adherent biofilms in man-made water systems. Disinfection efforts to prevent Legionella infections require a better understanding of the structures that promote Legionella surface attachment and biofilm colonization. Various enzymatic treatments, including multiple carbohydrate-targeting mixtures, failed to disrupt Legionella biofilms, despite the presence of carbohydrates in the biofilms as shown by biochemical methods and concanavalin-A lectin staining. Moreover, Legionella biofilms contained amyloids as detected by three microscopic staining methods (congo red, thioflavin T, and the amyloid-specific antibody WO2). Amyloid structures were seen in biofilms of both L. pneumophila and L. longbeachae, the two Legionella species most associated with human infection. Inhibition of amyloid assembly by congo red and thioflavin T limited both self-aggregation and surface attachment of L. pneumophila, indicating that functional amyloid structures have a key role in initial biofilm formation by these pathogenic bacteria.

Bacterial Amyloid and DNA are Important Constituents of Senile Plaques: Further Evidence of the Spirochetal and Biofilm Nature of Senile Plaques

It has long been known that spirochetes form clumps or micro colonies in vitro and in vivo. Cortical spirochetal colonies in syphilitic dementia were considered as reproductive centers for spirochetes. Historic and recent data demonstrate that senile plaques in Alzheimer’s disease (AD) are made up by spirochetes. Spirochetes, are able to form biofilm in vitro. Senile plaques are also reported to contain elements of biofilm constituents. We expected that AβPP and Aβ (the main components of senile plaques) also occur in pure spirochetal biofilms, and bacterial DNA (an important component of biofilm) is also present in senile plaques. Histochemical, immunohistochemical, and in situ hybridization techniques and the TUNEL assay were used to answer these questions. The results obtained demonstrate that Aβ and DNA, including spirochete-specific DNA, are key components of both pure spirochetal biofilms and senile plaques in AD and confirm the biofilm nature of senile plaques. These results validate validate previous observations that AβPP and/or an AβPP-like amyloidogenic protein are an integral part of spirochetes, and indicate that bacterial and host derived Aβ are both constituents of senile plaques. DNA fragmentation in senile plaques further confirms their bacterial nature and provides biochemical evidence for spirochetal cell death. Spirochetes evade host defenses, locate intracellularly, form more resistant atypical forms and notably biofilms, which contribute to sustain chronic infection and inflammation and explain the slowly progressive course of dementia in AD. To consider co-infecting microorganisms is equally important, as multi-species biofilms result in a higher resistance to treatments and a more severe dementia.

Intestinal bacterial biofilms modulate mucosal immune responses

Host-associated microbial communities modulate numerous aspects of host physiology at the epithelial interface within mucosal environments. Perturbations to this symbiotic relationship between host and microbiota has been linked to numerous microbial-driven pathological states, including Crohn's disease (CD). This is in part driven by the outgrowth of aggressive resident bacterial strains such as adherent and invasive Escherichia coli (AIEC) and changes in bacterial physiology and function that promote enhanced mucosal association of pathobionts and aberrant stimulation of mucosal immunity. Endogenous bacteria from host-associated microbial communities can adopt a sessile lifestyle and form multicellular structures known as biofilms that are generated through the expression of extracellular adhesion factors that include curli amyloid fibrils, cellulose and type 1 pili. In addition to enabling bacterial attachment to mucosal surfaces, biofilm components also stimulate immune responses and can therefore instigate or perpetuate microbial-driven inflammatory diseases such as CD. These host-bacterial interactions provide pharmacological targets that can potentially be exploited to limit mucosal adherence of aggressive enteric bacteria, inappropriate stimulation of inflammatory immune responses and consequent development of chronic intestinal inflammation.

Epibiont growth on filamentous bacteria found in activated sludge: a morphological approach

Occurrence of epibiont attachment on filamentous bacteria is a common phenomenon in activated sludge. In this study, an attempt has been made to elucidate the intrinsic nature of the attachment between the epibionts and filamentous bacteria based on microscopic observations. Characterization of the epiflora based on fluorescence in situ hybridization using group level probes revealed that the epibionts colonizing these filamentous bacteria largely belongs to the class Alphaproteobacteria, followed by Beta and Gammaproteobacteria. The ultrastructural examination using transmission electron microscopy pointed to the existence of a possible cell-to-cell interaction between epibionts and the selected filaments. Common bacterial appendages such as pili and fimbria were absent at the interface and further noted was the presence of cell membrane extensions on epibiont bacteria protruding towards the targeted filamentous cell. Fibrillar structures resembling amyloid-like proteins were observed within the filament cells targeted by the epibionts. An interaction was apparent between amyloid such as proteins and epibionts with regards to the direction of fibrillar structures and the distance of approaching epibiont bacteria. Due to the lack of visual evidence in support of penetration, the role of these amyloid-like fibrils as potential attachment sites for the epibionts was taken into consideration, and required further validation using conformational antibodies.

Direct Identification of Functional Amyloid Proteins by Label-Free Quantitative Mass Spectrometry

Functional amyloids are important structural and functional components of many biofilms, yet our knowledge of these fascinating polymers is limited to a few examples for which the native amyloids have been isolated in pure form. Isolation of the functional amyloids from other cell components represents a major bottleneck in the search for new functional amyloid systems. Here we present a label-free quantitative mass spectrometry method that allows identification of amyloid proteins directly in cell lysates. The method takes advantage of the extreme structural stability and polymeric nature of functional amyloids and the ability of concentrated formic acid to depolymerize the amyloids. An automated data processing pipeline that provides a short list of amyloid protein candidates was developed based on an amyloid-specific sigmoidal abundance signature in samples treated with increasing concentrations of formic acid. The method was evaluated using the Escherichiacoli curli and the Pseudomonas Fap system. It confidently identified the major amyloid subunit for both systems, as well as the minor subunit for the curli system. A few non-amyloid proteins also displayed the sigmoidal abundance signature. However, only one of these contained a sec-dependent signal peptide, which characterizes most of all secreted proteins, including all currently known functional bacterial amyloids.

Self-assembling peptide and protein amyloids: from structure to tailored function in nanotechnology

Self-assembled peptide and protein amyloid nanostructures have traditionally been considered only as pathological aggregates implicated in human neurodegenerative diseases. In more recent times, these nanostructures have found interesting applications as advanced materials in biomedicine, tissue engineering, renewable energy, environmental science, nanotechnology and material science, to name only a few fields. In all these applications, the final function depends on: (i) the specific mechanisms of protein aggregation, (ii) the hierarchical structure of the protein and peptide amyloids from the atomistic to mesoscopic length scales and (iii) the physical properties of the amyloids in the context of their surrounding environment (biological or artificial). In this review, we will discuss recent progress made in the field of functional and artificial amyloids and highlight connections between protein/peptide folding, unfolding and aggregation mechanisms, with the resulting amyloid structure and functionality. We also highlight current advances in the design and synthesis of amyloid-based biological and functional materials and identify new potential fields in which amyloid-based structures promise new breakthroughs.

The propensity of the bacterial rodlin protein RdlB to form amyloid fibrils determines its function in Streptomyces coelicolor

Streptomyces bacteria form reproductive aerial hyphae that are covered with a pattern of pairwise aligned fibrils called rodlets. The presence of the rodlet layer requires two homologous rodlin proteins, RdlA and RdlB, and the functional amyloid chaplin proteins, ChpA-H. In contrast to the redundancy shared among the eight chaplins, both RdlA and RdlB are indispensable for the establishment of this rodlet structure. By using a comprehensive biophysical approach combined with in vivo characterization we found that RdlB, but not RdlA, readily assembles into amyloid fibrils. The marked difference in amyloid propensity between these highly similar proteins could be largely attributed to a difference in amino acid sequence at just three sites. Further, an engineered RdlA protein in which these three key amino acids were replaced with the corresponding residues from RdlB could compensate for loss of RdlB and restore formation of the surface-exposed amyloid layer in bacteria. Our data reveal that RdlB is a new functional amyloid and provide a biophysical basis for the functional differences between the two rodlin proteins. This study enhances our understanding of how rodlin proteins contribute to formation of an outer fibrillar layer during spore morphogenesis in streptomycetes.

Epigallocatechin Gallate Remodels Overexpressed Functional Amyloids in Pseudomonas aeruginosa and Increases Biofilm Susceptibility to Antibiotic Treatment

Epigallocatechin-3-gallate (EGCG) is the major polyphenol in green tea. It has antimicrobial properties and disrupts the ordered structure of amyloid fibrils involved in human disease. The antimicrobial effect of EGCG against the opportunistic pathogen Pseudomonas aeruginosa has been shown to involve disruption of quorum sensing (QS). Functional amyloid fibrils in P. aeruginosa (Fap) are able to bind and retain quorum-sensing molecules, suggesting that EGCG interferes with QS through structural remodeling of amyloid fibrils. Here we show that EGCG inhibits the ability of Fap to form fibrils; instead, EGCG stabilizes protein oligomers. Existing fibrils are remodeled by EGCG into non-amyloid aggregates. This fibril remodeling increases the binding of pyocyanin, demonstrating a mechanism by which EGCG can affect the QS function of functional amyloid. EGCG reduced the amyloid-specific fluorescent thioflavin T signal in P. aeruginosa biofilms at concentrations known to exert an antimicrobial effect. Nanoindentation studies showed that EGCG reduced the stiffness of biofilm containing Fap fibrils but not in biofilm with little Fap. In a combination treatment with EGCG and tobramycin, EGCG had a moderate effect on the minimum bactericidal eradication concentration against wild-type P. aeruginosa biofilms, whereas EGCG had a more pronounced effect when Fap was overexpressed. Our results provide a direct molecular explanation for the ability of EGCG to disrupt P. aeruginosa QS and modify its biofilm and strengthens the case for EGCG as a candidate in multidrug treatment of persistent biofilm infections.

Extremely high UV-C radiation resistant microorganisms from desert environments with different manganese concentrations

Desiccation resistance and a high intracellular Mn/Fe ratio contribute to ionizing radiation resistance of Deinococcus radiodurans. We hypothesized that this was a general phenomenon and thus developed a strategy to search for highly radiation-resistant organisms based on their natural environment. While desiccation is a typical feature of deserts, the correlation between radiation resistance and the intracellular Mn/Fe ratio of indigenous microorganisms or the Mn/Fe ratio of the environment, has not yet been described. UV-C radiation is highly damaging to biomolecules including DNA. It was used in this study as a selective tool because of its relevance to early life on earth, high altitude aerobiology and the search for life beyond Earth. Surface soil samples were collected from the Sonoran Desert, Arizona (USA), from the Atacama Desert in Chile and from a manganese mine in northern Argentina. Microbial isolates were selected after exposure to UV-C irradiation and growth. The isolates comprised 28 genera grouped within six phyla, which we ranked according to their resistance to UV-C irradiation. Survival curves were performed for the most resistant isolates and correlated with their intracellular Mn/Fe ratio, which was determined by ICP-MS. Five percent of the isolates were highly resistant, including one more resistant than D. radiodurans, a bacterium generally considered the most radiation-resistant organism, thus used as a model for radiation resistance studies. No correlation was observed between the occurrence of resistant microorganisms and the Mn/Fe ratio in the soil samples. However, all resistant isolates showed an intracellular Mn/Fe ratio much higher than the sensitive isolates. Our findings could represent a new front in efforts to harness mechanisms of UV-C radiation resistance from extreme environments.

Common mechanisms involved in Alzheimer's disease and type 2 diabetes: a key role of chronic bacterial infection and inflammation

Strong epidemiologic evidence and common molecular mechanisms support an association between Alzheimer's disease (AD) and type 2-diabetes. Local inflammation and amyloidosis occur in both diseases and are associated with periodontitis and various infectious agents. This article reviews the evidence for the presence of local inflammation and bacteria in type 2 diabetes and discusses host pathogen interactions in chronic inflammatory disorders. Chlamydophyla pneumoniae, Helicobacter pylori and spirochetes are demonstrated in association with dementia and brain lesions in AD and islet lesions in type 2 diabetes. The presence of pathogens in host tissues activates immune responses through Toll-like receptor signaling pathways. Evasion of pathogens from complement-mediated attack results in persistent infection, inflammation and amyloidosis. Amyloid beta and the pancreatic amyloid called amylin bind to lipid bilayers and produce Ca(2+) influx and bacteriolysis. Similarly to AD, accumulation of amylin deposits in type 2 diabetes may result from an innate immune response to chronic bacterial infections, which are known to be associated with amyloidosis. Further research based on an infectious origin of both AD and type 2 diabetes may lead to novel treatment strategies.

Functional bacterial amyloid increases Pseudomonas biofilm hydrophobicity and stiffness

The success of Pseudomonas species as opportunistic pathogens derives in great part from their ability to form stable biofilms that offer protection against chemical and mechanical attack. The extracellular matrix of biofilms contains numerous biomolecules, and it has recently been discovered that in Pseudomonas one of the components includes β-sheet rich amyloid fibrils (functional amyloid) produced by the fap operon. However, the role of the functional amyloid within the biofilm has not yet been investigated in detail. Here we investigate how the fap-based amyloid produced by Pseudomonas affects biofilm hydrophobicity and mechanical properties. Using atomic force microscopy imaging and force spectroscopy, we show that the amyloid renders individual cells more resistant to drying and alters their interactions with hydrophobic probes. Importantly, amyloid makes Pseudomonas more hydrophobic and increases biofilm stiffness 20-fold. Deletion of any one of the individual members of in the fap operon (except the putative chaperone FapA) abolishes this ability to increase biofilm stiffness and correlates with the loss of amyloid. We conclude that amyloid makes major contributions to biofilm mechanical robustness.

Bacterial amyloid formation: structural insights into curli biogensis

Curli are functional amyloid fibers assembled by many Gram-negative bacteria as part of an extracellular matrix that encapsulates the bacteria within a biofilm. A multicomponent secretion system ensures the safe transport of the aggregation-prone curli subunits across the periplasm and outer membrane, and coordinates subunit self-assembly into surface-attached fibers. To avoid the build-up of potentially toxic intracellular protein aggregates, the timing and location of the interactions of the different curli proteins are of paramount importance. Here we review the structural and molecular biology of curli biogenesis, with a focus on the recent breakthroughs in our understanding of subunit chaperoning and secretion. The mechanistic insight into the curli assembly pathway will provide tools for new biotechnological applications and inform the design of targeted inhibitors of amyloid polymerization and biofilm formation.

The Tubular Sheaths Encasing Methanosaeta thermophila Filaments Are Functional Amyloids

Archaea are renowned for their ability to thrive in extreme environments, although they can be found in virtually all habitats. Their adaptive success is linked to their unique cell envelopes that are extremely resistant to chemical and thermal denaturation and that resist proteolysis by common proteases. Here we employ amyloid-specific conformation antibodies and biophysical techniques to show that the extracellular cell wall sheaths encasing the methanogenic archaea Methanosaeta thermophila PT are functional amyloids. Depolymerization of sheaths and subsequent MS/MS analyses revealed that the sheaths are composed of a single major sheath protein (MspA). The amyloidogenic nature of MspA was confirmed by in vitro amyloid formation of recombinant MspA under a wide range of environmental conditions. This is the first report of a functional amyloid from the archaeal domain of life. The amyloid nature explains the extreme resistance of the sheath, the elastic properties that allow diffusible substrates to penetrate through expandable hoop boundaries, and how the sheaths are able to split and elongate outside the cell. The archaeal sheath amyloids do not share homology with any of the currently known functional amyloids and clearly represent a new function of the amyloid protein fold.

New insight into the molecular control of bacterial functional amyloids

Amyloid protein structure has been discovered in a variety of functional or pathogenic contexts. What distinguishes the former from the latter is that functional amyloid systems possess dedicated molecular control systems that determine the timing, location, and structure of the fibers. Failure to guide this process can result in cytotoxicity, as observed in several pathologies like Alzheimer's and Parkinson's Disease. Many gram-negative bacteria produce an extracellular amyloid fiber known as curli via a multi-component secretion system. During this process, aggregation-prone, semi-folded curli subunits have to cross the periplasm and outer-membrane and self-assemble into surface-attached fibers. Two recent breakthroughs have provided molecular details regarding periplasmic chaperoning and subunit secretion. This review offers a combined perspective on these first mechanistic insights into the curli system.

The case for involvement of spiroplasma in the pathogenesis of transmissible spongiform encephalopathies

Spiroplasma biofilm formation explains the role of these wall-less bacteria in the pathogenesis of transmissible spongiform encephalopathies (TSEs). Spiroplasma embedded in the biofilm polysaccharide matrix are markedly resistant to physical and chemical treatment, simulating the biologic properties of the TSE agent. Microcolonies of spiroplasma embedded in biofilm bound to clay are the likely mechanism of lateral transmission of scrapie in sheep and chronic wasting disease in deer via soil ingestion. Spiroplasma in biofilm bound to the stainless steel of surgical instruments may also cause iatrogenic transmission of Creutzfeldt-Jakob disease. Sessile spiroplasma in biofilm attach to the surface by curli-like fibrils, a functional amyloid that is important for spiroplasma entering cells. Curli fibers have been shown to interact with host proteins and initiate formation of a potentially toxic amyloid that multiplies by self-assembly. In TSE, this mechanism may explain how spiroplasma trigger the formation of prion amyloid. This possibility is supported by experiments that show spiroplasma produce α-synuclein in mammalian tissue cultures. The data linking spiroplasma to neurodegenerative diseases provide a rationale for developing diagnostic tests for TSE based on the presence of spiroplasma-specific proteins or nucleic acid. Research efforts should focus on this bacterium for development of therapeutic regimens for Creutzfeldt-Jakob disease.

Advanced techniques for in situ analysis of the biofilm matrix (structure, composition, dynamics) by means of laser scanning microscopy

The extracellular constituents in bioaggregates and biofilms can be imaged four dimensionally by using laser scanning microscopy. In this protocol we provide guidance on how to examine the various extracellular compartments in between microbial cells and communities associated with interfaces. The current options for fluorescence staining of matrix compounds and extracellular microhabitats are presented. Furthermore, practical aspects are discussed and useful notes are added. The chapter ends with a brief introduction to other approaches for EPS analysis and an outlook for future needs.

Investigation of microbial biofilm structure by laser scanning microscopy

Microbial bioaggregates and biofilms are hydrated three-dimensional structures of cells and extracellular polymeric substances (EPS). Microbial communities associated with interfaces and the samples thereof may come from natural, technical, and medical habitats. For imaging such complex microbial communities confocal laser scanning microscopy (CLSM) is the method of choice. CLSM allows flexible mounting and noninvasive three-dimensional sectioning of hydrated, living, as well as fixed samples. For this purpose a broad range of objective lenses is available having different working distance and resolution. By means of CLSM the signals detected may originate from reflection, autofluorescence, reporter genes/fluorescence proteins, fluorochromes binding to specific targets, or other probes conjugated with fluorochromes. Recorded datasets can be used not only for visualization but also for semiquantitative analysis. As a result CLSM represents a very useful tool for imaging of microbiological samples in combination with other analytical techniques.

Geodermatophilus soli sp. nov. and Geodermatophilus terrae sp. nov., two actinobacteria isolated from grass soil

Two strains, PB34T and PB261T, were isolated from grass soil sampled in Daejeon, Republic of Korea. Comparative 16S rRNA gene sequence studies showed the two bacteria to be clearly affiliated with the phylum Actinobacteria and most closely related to the genus Geodermatophilus , showing 16S rRNA gene sequence similarities to the type strains of species of the genus Geodermatophilus of 95.0–96.3 % and sharing 98.5 % similarity between the two strains. The two strains were Gram-stain-positive, aerobic, motile and rod-shaped bacteria. The peptidoglycan contained meso-diaminopimelic acid as the diagnostic diamino acid. The predominant menaquinones were MK-9(H4) and MK-9(H0). The major fatty acids were iso-C15 : 0, iso-C16 : 0, iso-C17 : 0 and summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c) for strain PB34T and iso-C14 : 0, iso-C15 : 0, iso-C16 : 0 and C16 : 0 for strain PB261T. The G+C contents of the genomic DNA of strains PB34T and PB261T were 73.2 mol% and 74.1 mol%, respectively. Thus, based on the evidence of a polyphasic study, it is proposed that strains PB34T and PB261T represent two novel species, for which the names Geodermatophilus soli sp. nov. (type strain PB34T = KCTC 19880T = JCM 17785T) and Geodermatophilus terrae sp. nov. (type strain PB261T = KCTC 19881T = JCM 17786T) are proposed.

Expression of Fap amyloids in Pseudomonas aeruginosa, P. fluorescens, and P. putida results in aggregation and increased biofilm formation

The fap operon, encoding functional amyloids in Pseudomonas (Fap), is present in most pseudomonads, but so far the expression and importance for biofilm formation has only been investigated for P. fluorescens strain UK4. In this study, we demonstrate the capacity of P. aeruginosa PAO1, P. fluorescens Pf-5, and P. putida F1 to express Fap fibrils, and investigated the effect of Fap expression on aggregation and biofilm formation. The fap operon in all three Pseudomonas species conferred the ability to express Fap fibrils as shown using a recombinant approach. This Fap overexpression consistently resulted in highly aggregative phenotypes and in increased biofilm formation. Detailed biophysical investigations of purified fibrils confirmed FapC as the main fibril monomer and supported the role of FapB as a minor, nucleating constituent as also indicated by bioinformatic analysis. Bioinformatics analysis suggested FapF and FapD as a potential β-barrel membrane pore and protease, respectively. Manipulation of the fap operon showed that FapA affects monomer composition of the final amyloid fibril, and that FapB is an amyloid protein, probably a nucleator for FapC polymerization. Our study highlights the fap operon as a molecular machine for functional amyloid formation.

Bacterial curli protein promotes the conversion of PAP248-286 into the amyloid SEVI: cross-seeding of dissimilar amyloid sequences

Fragments of prostatic acid phosphatase (PAP248-286) in human semen dramatically increase HIV infection efficiency by increasing virus adhesion to target cells. PAP248-286 only enhances HIV infection in the form of amyloid aggregates termed SEVI (Semen Enhancer of Viral Infection), however monomeric PAP248-286 aggregates very slowly in isolation. It has therefore been suggested that SEVI fiber formation in vivo may be promoted by exogenous factors. We show here that a bacterially-produced extracellular amyloid (curli or Csg) acts as a catalytic agent for SEVI formation from PAP248-286 at low concentrations in vitro, producing fibers that retain the ability to enhance HIV (Human Immunodeficiency Virus) infection. Kinetic analysis of the cross-seeding effect shows an unusual pattern. Cross-seeding PAP248-286 with curli only moderately affects the nucleation rate while significantly enhancing the growth of fibers from existing nuclei. This pattern is in contrast to most previous observations of cross-seeding, which show cross-seeding partially bypasses the nucleation step but has little effect on fiber elongation. Seeding other amyloidogenic proteins (IAPP (islet amyloid polypeptide) and Aβ1-40) with curli showed varied results. Curli cross-seeding decreased the lag-time of IAPP amyloid formation but strongly inhibited IAPP elongation. Curli cross-seeding exerted a complicated concentration dependent effect on Aβ1-40 fibrillogenesis kinetics. Combined, these results suggest that the interaction of amyloidogenic proteins with preformed fibers of a different type can take a variety of forms and is not limited to epitaxial nucleation between proteins of similar sequence. The ability of curli fibers to interact with proteins of dissimilar sequences suggests cross-seeding may be a more general phenomenon than previously supposed.

Microbial amyloids--functions and interactions within the host

The aggregation of proteins into amyloid fibers is a common characteristic of many neurodegenerative disorders including Alzheimer's, Parkinson's, and prion diseases. Amyloid formation was originally characterized in these systems and is traditionally viewed as a consequence of protein misfolding and aggregation. An emerging field of study brings functional amyloids, like those produced by bacteria, into the scientific mainstream, and demonstrates a ubiquitous role for amyloids in living systems. This review aims to summarize what is known about the bacterial amyloids and their interactions within various host environments.

Exploiting amyloid: how and why bacteria use cross-β fibrils

Many bacteria produce protein fibrils that are structurally analogous to those associated with protein misfolding diseases such as Alzheimer's disease. However, unlike fibrils associated with disease, bacterial amyloids have beneficial functions including conferring stability to biofilms, regulating development or imparting virulence. In the present review, we consider what makes amyloid fibrils so suitable for these roles and discuss recent developments in the study of bacterial amyloids, in particular the chaplins from Streptomyces coelicolor. We also consider the broader impact of the study of bacterial amyloids on our understanding of infection and disease and on developments in nanotechnology.

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

Curli fibrils, the best-characterized functional bacterial amyloids, are an important component of enterobacterial biofilms. We have previously shown that curli fibrils are recognized by the Toll-like receptor 2 (TLR2)/TLR1 heterodimer complex. Utilizing polarized T-84 cells, an intestinal epithelial cell line derived from colon carcinoma grown on semipermeable tissue culture inserts, we determined that infection with a Salmonella enterica serovar Typhimurium csgBA mutant, which does not express curli, resulted in an increase in intestinal barrier permeability and an increase in bacterial translocation compared to infection with curliated wild-type S. Typhimurium. When the TLR2 downstream signaling molecule phosphatidylinositol 3-kinase (PI3K) was blocked using wortmannin or LY294002, the difference in disruption of the intestinal epithelium and bacterial translocation was no longer observed. Additionally, disruption of polarized T-84 cells treated basolaterally with the TLR5 ligand flagellin was prevented when the polarized cells were simultaneously treated with the synthetic TLR2/TLR1 ligand Pam(3)CSK(4) or with purified curli fibrils in the apical compartment. Similar to in vitro observations, C57BL/6 mice infected with the csgBA mutant suffered increased disruption of the intestinal epithelium and therefore greater dissemination of the bacteria to the mesenteric lymph nodes than mice infected with wild-type S. Typhimurium. The differences in disruption of the intestinal epithelium and bacterial dissemination in the mice infected with csgBA mutant or wild-type S. Typhimurium were not apparent in TLR2-deficient mice. Overall, these studies report for the first time that activation of the TLR2/PI3K pathway by microbial amyloids plays a critical role in regulating the intestinal epithelial barrier as well as monitoring bacterial translocation during infection.

Microbial amyloids induce interleukin 17A (IL-17A) and IL-22 responses via Toll-like receptor 2 activation in the intestinal mucosa

The Toll-like receptor 2 (TLR2)/TLR1 receptor complex responds to amyloid fibrils, a common component of biofilm material produced by members of the phyla Firmicutes, Bacteroidetes, and Proteobacteria. To determine whether this TLR2/TLR1 ligand stimulates inflammatory responses when bacteria enter intestinal tissue, we investigated whether expression of curli amyloid fibrils by the invasive enteric pathogen Salmonella enterica serotype Typhimurium contributes to T helper 1 and T helper 17 responses by measuring cytokine production in the mouse colitis model. A csgBA mutant, deficient in curli production, elicited decreased expression of interleukin 17A (IL-17A) and IL-22 in the cecal mucosa compared to the S. Typhimurium wild type. In TLR2-deficient mice, IL-17A and IL-22 expression was blunted during S. Typhimurium infection, suggesting that activation of the TLR2 signaling pathway contributes to the expression of these cytokines. T cells incubated with supernatants from bone marrow-derived dendritic cells (BMDCs) treated with curli fibrils released IL-17A in a TLR2-dependent manner in vitro. Lower levels of IL-6 and IL-23 production were detected in the supernatants of the TLR2-deficient BMDCs treated with curli fibrils. Consistent with this, three distinct T-cell populations-CD4(+) T helper cells, cytotoxic CD8(+) T cells, and γδ T cells-produced IL-17A in response to curli fibrils in the intestinal mucosa during S. Typhimurium infection. Notably, decreased IL-6 expression by the dendritic cells and decreased IL-23 expression by the dendritic cells and macrophages were observed in the cecal mucosa of mice infected with the curli mutant. We conclude that TLR2 recognition of bacterial amyloid fibrils in the intestinal mucosa represents a novel mechanism of immunoregulation, which contributes to the generation of inflammatory responses, including production of IL-17A and IL-22, in response to bacterial entry into the intestinal mucosa.

Microbial manipulation of the amyloid fold

Microbial biofilms are encased in a protein, DNA, and polysaccharide matrix that protects the community, promotes interactions with the environment, and helps cells adhere together. The protein component of these matrices is often a remarkably stable, β-sheet-rich polymer called amyloid. Amyloids form ordered, self-templating fibers that are highly aggregative, making them a valuable biofilm component. Some eukaryotic proteins inappropriately adopt the amyloid fold, and these misfolded protein aggregates disrupt normal cellular proteostasis, which can cause significant cytotoxicity. Indeed, until recently amyloids were considered solely the result of protein misfolding. However, research over the past decade has revealed how various organisms have capitalized on the amyloid fold by developing sophisticated biogenesis pathways that coordinate gene expression, protein folding, and secretion so that amyloid-related toxicities are minimized. How microbes manipulate amyloids, by augmenting their advantageous properties and by reducing their undesirable properties, will be the subject of this review.

Promiscuous cross-seeding between bacterial amyloids promotes interspecies biofilms

Amyloids are highly aggregated proteinaceous fibers historically associated with neurodegenerative conditions including Alzheimers, Parkinsons, and prion-based encephalopathies. Polymerization of amyloidogenic proteins into ordered fibers can be accelerated by preformed amyloid aggregates derived from the same protein in a process called seeding. Seeding of disease-associated amyloids and prions is highly specific and cross-seeding is usually limited or prevented. Here we describe the first study on the cross-seeding potential of bacterial functional amyloids. Curli are produced on the surface of many Gram-negative bacteria where they facilitate surface attachment and biofilm development. Curli fibers are composed of the major subunit CsgA and the nucleator CsgB, which templates CsgA into fibers. Our results showed that curli subunit homologs from Escherichia coli, Salmonella typhimurium LT2, and Citrobacter koseri were able to cross-seed in vitro. The polymerization of Escherichia coli CsgA was also accelerated by fibers derived from a distant homolog in Shewanella oneidensis that shares less than 30% identity in primary sequence. Cross-seeding of curli proteins was also observed in mixed colony biofilms with E. coli and S. typhimurium. CsgA was secreted from E. coli csgB- mutants assembled into fibers on adjacent S. typhimurium that presented CsgB on its surfaces. Similarly, CsgA was secreted by S. typhimurium csgB- mutants formed curli on CsgB-presenting E. coli. This interspecies curli assembly enhanced bacterial attachment to agar surfaces and supported pellicle biofilm formation. Collectively, this work suggests that the seeding specificity among curli homologs is relaxed and that heterogeneous curli fibers can facilitate multispecies biofilm development.

Spiroplasma spp. biofilm formation is instrumental for their role in the pathogenesis of plant, insect and animal diseases

Spiroplasma spp. are important phyto and insect pathogens, and candidate causal agent/s of transmissible spongiform encephalopathies (TSE) in man and animals. These filterable wall-less bacteria are widely distributed in nature with an unspecified environmental reservoir. In this study we showed by scanning electron microscopy that spiroplasma form biofilm on an assortment of hard surfaces including mica, nickel and stainless steel. Spiroplasma were stuck to the surfaces by fibrillar threads consistent with curli fibers (an amyloid protein found in bacterial biofilms). After a lengthy time in cultures (6 weeks), spiroplasma in biofilm bound to mica disks lost their spiral shapes and formed coccoid forms interconnected by long (>2 μm) branched membranous nanotubules, therein representing direct conjugate connections between the cells. The affinity of spiroplasma biofilms for mica and nickel, and the membrane communications suggest that soil could be a reservoir for these bacteria. The persistence of clay bound spiroplasma in soil could serve as the mechanism of lateral spread of TSEs by ingestion of soil by ruminants. Spiroplasma binding to stainless steel wire supports bacterial contamination of surgical instruments following surgery on dementia patients as a mechanism of iatrogenic transmission of TSEs, especially with resistance of spiroplasma in biofilms to drying or exposure to 50% glutaraldehyde. The discovery of biofilm formation by spiroplasma addresses questions regarding environmental persistence of these organisms in nature and suggests novel mechanisms of intercellular communication and transmission.

Static biofilm cultures of Gram-positive pathogens grown in a microtiter format used for anti-biofilm drug discovery

An in vitro assay is presented for culturing staphylococcal biofilms and biofilms of nonmotile Gram-positive bacteria under static conditions in microtiter assay plates, and for the quantification of biofilm growth, using a simple staining procedure that measures amounts of bacterial cells and extracellular matrix. This basic assay can be adapted readily to study several aspects of biofilm formation, for high-throughput screening to identify small molecule inhibitors of biofilm formation or biofilm-defective mutants, and for quantifying the anti-biofilm activity of biofilm inhibitors.

Emerging roles of pathogens in Alzheimer disease

Chronic spirochetal infection can cause slowly progressive dementia, cortical atrophy and amyloid deposition in the atrophic form of general paresis. There is a significant association between Alzheimer disease (AD) and various types of spirochete (including the periodontal pathogen Treponemas and Borrelia burgdorferi), and other pathogens such as Chlamydophyla pneumoniae and herpes simplex virus type-1 (HSV-1). Exposure of mammalian neuronal and glial cells and organotypic cultures to spirochetes reproduces the biological and pathological hallmarks of AD. Senile-plaque-like beta amyloid (Aβ) deposits are also observed in mice following inhalation of C. pneumoniae in vivo, and Aβ accumulation and phosphorylation of tau is induced in neurons by HSV-1 in vitro and in vivo. Specific bacterial ligands, and bacterial and viral DNA and RNA all increase the expression of proinflammatory molecules, which activates the innate and adaptive immune systems. Evasion of pathogens from destruction by the host immune reactions leads to persistent infection, chronic inflammation, neuronal destruction and Aβ deposition. Aβ has been shown to be a pore-forming antimicrobial peptide, indicating that Aβ accumulation might be a response to infection. Global attention and action is needed to support this emerging field of research because dementia might be prevented by combined antibiotic, antiviral and anti-inflammatory therapy.

Wet-spinning of amyloid protein nanofibers into multifunctional high-performance biofibers

Amyloid nanofibers derived from hen egg white lysozyme were processed into macroscopic fibers in a wet-spinning process based on interfacial polyion complexation using a polyanionic polysaccharide as cross-linker. As a result of their amyloid nanostructure, the hierarchically self-assembled protein fibers have a stiffness of up to 14 GPa and a tensile strength of up to 326 MPa. Fine-tuning of the polyelectrolytic interactions via pH allows to trigger the release of small molecules, as demonstrated with riboflavin-5'-phophate. The amyloid fibrils, highly oriented within the gellan gum matrix, were mineralized with calcium phosphate, mimicking the fibrolamellar structure of bone. The formed mineral crystals are highly oriented along the nanofibers, thus resulting in a 9-fold increase in fiber stiffness.

Alzheimer's disease - a neurospirochetosis. Analysis of the evidence following Koch's and Hill's criteria

It is established that chronic spirochetal infection can cause slowly progressive dementia, brain atrophy and amyloid deposition in late neurosyphilis. Recently it has been suggested that various types of spirochetes, in an analogous way to Treponema pallidum, could cause dementia and may be involved in the pathogenesis of Alzheimer's disease (AD). Here, we review all data available in the literature on the detection of spirochetes in AD and critically analyze the association and causal relationship between spirochetes and AD following established criteria of Koch and Hill. The results show a statistically significant association between spirochetes and AD (P = 1.5 × 10-17, OR = 20, 95% CI = 8-60, N = 247). When neutral techniques recognizing all types of spirochetes were used, or the highly prevalent periodontal pathogen Treponemas were analyzed, spirochetes were observed in the brain in more than 90% of AD cases. Borrelia burgdorferi was detected in the brain in 25.3% of AD cases analyzed and was 13 times more frequent in AD compared to controls. Periodontal pathogen Treponemas (T. pectinovorum, T. amylovorum, T. lecithinolyticum, T. maltophilum, T. medium, T. socranskii) and Borrelia burgdorferi were detected using species specific PCR and antibodies. Importantly, co-infection with several spirochetes occurs in AD. The pathological and biological hallmarks of AD were reproduced in vitro by exposure of mammalian cells to spirochetes. The analysis of reviewed data following Koch's and Hill's postulates shows a probable causal relationship between neurospirochetosis and AD. Persisting inflammation and amyloid deposition initiated and sustained by chronic spirochetal infection form together with the various hypotheses suggested to play a role in the pathogenesis of AD a comprehensive entity. As suggested by Hill, once the probability of a causal relationship is established prompt action is needed. Support and attention should be given to this field of AD research. Spirochetal infection occurs years or decades before the manifestation of dementia. As adequate antibiotic and anti-inflammatory therapies are available, as in syphilis, one might prevent and eradicate dementia.

Amyloid histology stain for rapid bacterial endospore imaging

Bacterial endospores are some of the most resilient forms of life known to us, with their persistent survival capability resulting from a complex and effective structural organization. The outer membrane of endospores is surrounded by the densely packed endospore coat and exosporium, containing amyloid or amyloid-like proteins. In fact, it is the impenetrable composition of the endospore coat and the exosporium that makes staining methodologies for endospore detection complex and challenging. Therefore, a plausible strategy for facile and expedient staining would be to target components of the protective surface layers of the endospores. Instead of targeting endogenous markers encapsulated in the spores, here we demonstrated staining of these dormant life entities that targets the amyloid domains, i.e., the very surface components that make the coats of these species impenetrable. Using an amyloid staining dye, thioflavin T (ThT), we examined this strategy. A short incubation of bacillus endospore suspensions with ThT, under ambient conditions, resulted in (i) an enhancement of the fluorescence of ThT and (ii) the accumulation of ThT in the endospores, affording fluorescence images with excellent contrast ratios. Fluorescence images revealed that ThT tends to accumulate in the surface regions of the endospores. The observed fluorescence enhancement and dye accumulation, coupled with the sensitivity of emission techniques, provide an effective and rapid means of staining endospores without the inconvenience of pre- or posttreatment of samples.