Functional amyloid formation by Streptococcus mutans

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.

Community interactions of oral streptococci

It is now clear that the most common oral diseases, dental caries and periodontitis, are caused by mixed-species communities rather than by individual pathogens working in isolation. Oral streptococci are central to these disease processes since they are frequently the first microorganisms to colonize oral surfaces and they are numerically the dominant microorganisms in the human mouth. Numerous interactions between oral streptococci and other bacteria have been documented. These are thought to be critical for the development of mixed-species oral microbial communities and for the transition from oral health to disease. Recent metagenomic studies are beginning to shed light on the co-occurrence patterns of streptococci with other oral bacteria. Refinements in microscopy techniques and biofilm models are providing detailed insights into the spatial distribution of streptococci in oral biofilms. Targeted genetic manipulation is increasingly being applied for the analysis of specific genes and networks that modulate interspecies interactions. From this work, it is clear that streptococci produce a range of extracellular factors that promote their integration into mixed-species communities and enable them to form social networks with neighboring taxa. These "community integration factors" include coaggregation-mediating adhesins and receptors, small signaling molecules such as peptides or autoinducer-2, bacteriocins, by-products of metabolism including hydrogen peroxide and lactic acid, and a range of extracellular enzymes. Here, we provide an overview of various types of community interactions between oral streptococci and other microorganisms, and we consider the possibilities for the development of new technologies to interfere with these interactions to help control oral biofilms.

An intramolecular interaction involving the N terminus of a streptococcal adhesin affects its conformation and adhesive function

BACKGROUND

P1 is an adhesin on the surface of Streptococcus mutans.

RESULTS

Destroying the high affinity interaction between the N and C termini of S. mutans P1 creates a non-adherent phenotype.

CONCLUSION

The N terminus facilitates proper folding, function, and stability within recombinant P1.

SIGNIFICANCE

The relationship between folding, maturation, and cell surface assembly is critical to understanding the P1 mechanism of action. The adhesin P1 is localized on the surface of the oral pathogen Streptococcus mutans and facilitates an interaction with the glycoprotein complex salivary agglutinin that is comprised primarily of the scavenger receptor gp340. Recent crystal structures of P1 display an unusual structure in which the protein folds back upon itself to form an elongated hybrid helical stalk with a globular head at the apex and a globular C-terminal region at the base. The N terminus of P1 has not yet been characterized. In this report we describe the contribution of an interaction between the N-terminal and C-terminal portions of the protein that is required for proper function of P1 on the surface of S. mutans. Utilizing recombinant N-terminal and C-terminal fragments, we employed isothermal titration calorimetry and native gel electrophoresis to demonstrate that these fragments form a high affinity and stable complex in solution. Furthermore, circular dichroism and surface plasmon resonance measurements indicated that the N-terminal fragment contributes to the folding and increases the functionality of the C-terminal fragment in trans. Finally, we utilized circular dichroism, surface plasmon resonance, and differential scanning calorimetry to show that an N-terminal 106-amino acid segment within P1 contributes to the proper folding and function of the full-length recombinant molecule and increases the stability of its elongated hybrid helical stalk.

Does Candida albicans Als5p amyloid play a role in commensalism in Caenorhabditis elegans?

Candida albicans, a dimorphic fungus and an opportunistic pathogen, possesses a myriad of adherence factors, including members of the agglutinin-like sequence (Als) family of mannoproteins. The adhesin Als5p mediates adhesion to many substrates and is upregulated during commensal interactions but is downregulated during active C. albicans infections. An amyloid-forming core sequence at residues 325 to 331 is important for Als5p function, because a single-amino-acid substitution at position 326 (V326N) greatly reduces Als5p-mediated adherence. We evaluated the role of Als5p in host-microbe interactions by using Caenorhabditis elegans nematodes as a host model and feeding them Saccharomyces cerevisiae expressing Als5p on the surface. Als5p-expressing yeast had 8.5- and 3.5-fold-increased intestinal accumulation rates compared to Als5p-nonexpressing S. cerevisiae or yeast expressing amyloid-deficient Als5p(V326N), respectively. Surprisingly, this accumulation delayed S. cerevisiae-induced killing of C. elegans. The median survival time was nearly twice as long as that of nematodes fed nonexpressing or non-amyloid-forming Als5p(V326N)-expressing S. cerevisiae. Treatment with the amyloid-inhibiting dye Congo red or repression of Als5p expression abrogated the protective effect of Als5p. Furthermore, Als5p had no effect on oocyte quantity or quality, since nematodes fed either empty vector (EV)- or Als5p(V326N)-expressing S. cerevisiae had similar egg-laying and egg-hatching rates. This study is the first, to our knowledge, to show that expression of an amyloid-forming protein can attenuate pathogenicity in C. elegans.

Streptococcus mutans: a new Gram-positive paradigm?

Despite the enormous contributions of the bacterial paradigms Escherichia coli and Bacillus subtilis to basic and applied research, it is well known that no single organism can be a perfect representative of all other species. However, given that some bacteria are difficult, or virtually impossible, to cultivate in the laboratory, that some are recalcitrant to genetic and molecular manipulation, and that others can be extremely dangerous to manipulate, the use of model organisms will continue to play an important role in the development of basic research. In particular, model organisms are very useful for providing a better understanding of the biology of closely related species. Here, we discuss how the lifestyle, the availability of suitable in vitro and in vivo systems, and a thorough understanding of the genetics, biochemistry and physiology of the dental pathogen Streptococcus mutans have greatly advanced our understanding of important areas in the field of bacteriology such as interspecies biofilms, competence development and stress responses. In this article, we provide an argument that places S. mutans, an organism that evolved in close association with the human host, as a novel Gram-positive model organism.