You will be presented with the abstract, introduction, and discussion section from a biomedical research article. Your task is to create a summary that a layperson can understand, capturing the essence of the research article. Keep essential scientific terms, but ensure that the language remains clear and the concepts are explained in an uncomplicated manner.

Title: Functional Amyloids Composed of Phenol Soluble Modulins Stabilize Staphylococcus aureus Biofilms}
Article:
Abstract:
Staphylococcus aureus is an opportunistic pathogen that colonizes the skin and mucosal surfaces of mammals. Persistent staphylococcal infections often involve surface-associated communities called biofilms. Here we report the discovery of a novel extracellular fibril structure that promotes S. aureus biofilm integrity. Biochemical and genetic analysis has revealed that these fibers have amyloid-like properties and consist of small peptides called phenol soluble modulins( PSMs). Mutants unable to produce PSMs were susceptible to biofilm disassembly by matrix degrading enzymes and mechanical stress. Previous work has associated PSMs with biofilm disassembly, and we present data showing that soluble PSM peptides disperse biofilms while polymerized peptides do not. This work suggests the PSMs' aggregation into amyloid fibers modulates their biological activity and role in biofilms.
Introduction:
Staphylococcus aureus is the causative agent of numerous diseases ranging from relatively benign skin conditions to fatal systemic infections. Formation of bacterial biofilms on host tissues and implanted materials contributes to chronic S. aureus infections, as biofilms are exceptionally resistant to host immune response and chemotherapies[1]. Biofilms are multicellular structures encased in a matrix of proteins, polysaccharides, extracellular DNA, and other environmental factors[1],[2]. Biomolecules that digest matrix components( e. g., proteases, DNases, and glycoside hydrolases) can disrupt established biofilms and render detached cells susceptible to antimicrobials[3],[4],[5],[6],[7]. The precise composition of the biofilm matrix varies greatly by strain, physiological state, and nutrient availability[5],[8],[9],[10],[11],[12]. In this study, we examined how growth media affects the composition of the biofilm matrix. This led to the discovery of an extracellular fibril structure in S. aureus biofilms grown in a non-standard rich media. These fibers share morphological and biophysical characteristics with functional bacterial amyloids such as curli in Escherichia coli biofilms, TasA of Bacillus subtilis, and the Fap fimbriae in Pseudomonas aeruginosa[13],[14],[15],[16]. Biochemical and genetic analysis revealed that these fibril structures are composed of small peptides called phenol soluble modulins( PSMs). Mutants incapable of producing PSMs formed biofilms that were susceptible to disassembly by enzymatic degradation and mechanical stress. Previous work has demonstrated that PSMs are surfactant-like peptides that promote biofilm disassembly[17],[18],[19],[20],[21]; exhibit antimicrobial activity against niche bacteria[22],[23],[24]; hinder host immune response by recruiting and lysing neutrophils; and are abundant virulence factors produced by community-associated MRSA strains( CA-MRSA)[18],[25],[26],[27]. The genes encoding the core family of PSM peptides are highly conserved across S. aureus strains: four are expressed from the alpha( αpsm1–4) operon, two are expressed from the beta( βpsm1&2) operon, and the delta hemolysin( hld) is encoded within the regulatory RNA, RNAIII[28],[29],[30]. The significance of the PSMs has only recently been investigated because the coding sequences of the αpsm & βpsm peptides are small enough to have eluded detection by conventional gene annotation programs, and they are still poorly annotated in public databases[29],[30]. We have found that ordered aggregation of PSM peptides into amyloid-like fibers can abrogate the biofilm disassembly activity ascribed to monomeric PSM peptides[12],[17],[18],[19],[20],[21]. Our findings suggest that PSMs can modulate biofilm disassembly using amyloid-like aggregation as a control point for their activity. This is the first report to identify and characterize extracellular fimbriae in the S. aureus biofilm, and our research could lead to new approaches in treating persistent biofilm associated infections.
Discussion:
Biofilm formation and disassembly are carefully coordinated with the production and breakdown of matrix components. The biofilm lifecycle of attachment, maturation, and disassembly participates as a mechanism of virulence in many persistent S. aureus infections[1],[2],[4],[5],[11],[12],[19]. A better understanding of the dynamic S. aureus matrix environment may inspire new, innovative techniques for controlling biofilm infections. Previous studies have shown that the S. aureus biofilm matrix contains polysaccharides and DNA that interact with structural and enzymatic proteins[3],[4],[5],[7],[41]. In this work we demonstrate that under certain growth conditions, S. aureus produces amyloid-like fibers that contribute to biofilm integrity( Fig. 1, 2, 7). Purification and analysis of fibers revealed that several small peptides of the phenol soluble modulin family were present( Fig. 3 & Fig. 4). Fibers were not detected in biofilms of an Δαβpsm deletion mutant under the same conditions that favor their production in wildtype strains( Fig. 5). Δαβpsm mutant biofilms were further demonstrated to be significantly more susceptible to disassembly with matrix degrading enzymes and mechanical stress than their isogenic parent( Fig. 7). To the best of our knowledge, this is the first report describing an extracellular fibril structure in S. aureus biofilms. We refer to these matrix components as being amyloid-like because they possess some of the characteristics often attributed to amyloid proteins: fibril morphology( Fig. 2, 5, 6, 8), relative SDS insolubility( Fig. 1 & Fig. 3), binding to the amyloid-specific dyes thioflavin T and Congo red( Fig. 6 & Fig. 8), and they display β-sheet structure[14],[31]. The observation that PSM peptides not only self-assemble, but contribute to the biofilm's structural integrity is intriguing in light of recent work describing the PSMs' involvement in biofilm disassembly[11],[20],[27]. It is well-documented that the PSMs are regulated by the agr quorum-sensing network[11],[12],[28],[42], and we similarly have found that an agr deficient strain did not produce fibers( Fig. 2D). This contributes to a growing body of evidence which implicates the agr system to have wide-ranging effects beyond heightened pathogenicity and biofilm dispersal[4],[20],[21],[43]. It is tempting to speculate that the media-dependent fiber production is somehow influencing agr regulation, perhaps through metabolism or through other signaling cues. PSMs were first isolated from Staphylococcus epidermidis cultures as a polypeptide complex, and have since been shown to interact biochemically[22],[29]. We have demonstrated that synthetic S. aureus PSM peptides are capable of self-assembling into amyloid-like fibers in vitro( Fig. 6A & Fig. 6B). These fibers demonstrate CR and ThT binding capacities similar to known amyloid proteins. PSMs, including δ-toxin have been previously characterized as amphipathic α helices[22],[30],[44],[45]. Our data indicate that soluble PSMs have a helical structure in solution, but transition to adopt a more β-rich structure after aggregation( Fig. 6E). The assembly of αPSM1 into fibers prevents the biofilm disassembly activity attributed to soluble peptides species( Fig. 7). We interpret these results as evidence that aggregation into amyloid fibers can regulate PSM activity in the microenvironment of the biofilm. Our findings demonstrate that S. aureus PSMs can be found in biofilms as fibrils, and may implicate fibril formation as a means of altering their activity and function. It is not known at this time what mechanisms influence the PSMs' ability to switch from a monomeric to fibril state, nor is it clear how this affects the formation and disassembly of biofilms. It is possible that PSM fibrillation is synchronized in vivo by a nucleator protein, similar to CsgB in E. coli[34]. Formylation may also play a role; the PSMs and δ-toxin are detected at the protein level both with and without with a formylated methionine modification[29],[30],[46],[47], and the PSMs identified in our MS analysis contained primarily deformylated N-methionines. Recent work demonstrates that non-N-formylated PSMs are strong activators of FPR2 receptors, which also respond to amyloidogenic peptides like Aβ1–42 and serum amyloid A[48],[49],[50], and may implicate a role for deformylation in fibril construction. We speculate that there are numerous other environmental cues( such as pH and osmolarity) driving the PSMs commitment to the fibrillation pathway, and this is currently under investigation. This study builds upon an emerging paradigm emphasizing that amyloid fibers are common in the biofilm matrices of many bacterial species. Curli fibers produced by pathogenic E. coli and other enterics were the first functional amyoloids to be characterized[15],[32],[33]. The gram-positive bacteria Streptomyces coelicolor produces several small peptide species, which have been shown to polymerize in vitro and in vivo to facilitate sporulation at the air-liquid interface[51],[52],[53],[54]. Recent work in B. subtilis has shown that the antimicrobial and spore coat protein TasA can assemble into amyloid-like fibrils during biofilm growth[16]. Even natural biofilms collected from a variety of environmental niches appear to contain amyloid-like fibers[55], indicating that the production of bacterial amyloids may be a shared feature of biofilm matrices from many different bacterial communities. We propose that amyloid-like aggregation of toxic proteins is an under appreciated form of posttranslational regulation utilized throughout nature, and even more examples continue to emerge. The antimicrobial activity of the Klebsiella pneumonia bacteriocin microcin E492 can be turned off through their assembly into amyloid-like fibers[56]. Recent work by Maji et al. has demonstrated that even human peptide hormones can form amyloid-like structures for storage[57]. Likewise, PSMs may be stored as inert fibrils in a sessile biofilm until conditions arise that favor their dissociation to promote biofilm disassembly, antimicrobial activity, or virulence. This work presents evidence that S. aureus PSMs can be found in biofilms as large fibril structures providing new insight into how quorum sensing and virulence play into the complexity of the biofilm lifecycle.
Most people know Staphylococcus aureus as a highly infectious “Super Bug” , but many are not aware that S . aureus non-infectiously colonizes much of the population in the nose , among other bodily niches . It is not well understood how and why S . aureus is able to adapt and readily switch between the commensal and pathogenic lifestyle within the host; however , the capacity to accumulate into multicellular aggregates is a hallmark associated with both lifestyles . In this work , we demonstrate that S . aureus produces extracellular fibers in multicellular biofilm communities , and that these fibers help the bacterial community to withstand physical stresses . Surprisingly , these fibers consist of small peptides called phenol soluble modulins ( PSMs ) that have previously been implicated in biofilm disassembly and virulence . We demonstrate that accumulation of PSM peptides into fibers modulates their ability to disperse biofilms . Thus , PSMs fulfill dual and opposing roles that are modulated by amyloid-like aggregation . Staphylococci have never before been shown to produce this kind of extracellular structure , and our findings may have a profound impact on our understanding of S . aureus physiology . We have found that these structures are composed of known virulence factors , which indicates a common pathway between infectious and static lifestyles in the body .