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The processes associated with early events in biofilm formation have become a major research focus over the past several years. Events associated with dispersion of cells from late stage biofilms have, however, received little attention. We demonstrate here that dispersal of Pseudomonas aeruginosa PAO1 from biofilms is inducible by a sudden increase in carbon substrate availability. Most efficient at inducing dispersal were sudden increases in availability of succinate > glutamate > glucose that led to ϳ80% reductions in surface-associated biofilm biomass. Nutrient-induced biofilm dispersion was associated with increased expression of flagella (fliC) and correspondingly decreased expression of pilus (pilA) genes in dispersed cells. Changes in gene expression associated with dispersion of P. aeruginosa biofilms were studied by using DNA microarray technology. Results corroborated proteomic data that showed gene expression to be markedly different between biofilms and newly dispersed cells. Gene families that were upregulated in dispersed cells included those for flagellar and ribosomal proteins, kinases, and phage PF1. Within the biofilm, genes encoding a number of denitrification pathways and pilus biosynthesis were also upregulated. Interestingly, nutrient-induced dispersion was associated with an increase in the number of Ser/Thr-phosphorylated proteins within the newly dispersed cells, and inhibition of dephosphorylation reduced the extent of nutrient-induced dispersion. This study is the first to demonstrate that dispersal of P. aeruginosa from biofilms can be induced by the addition of simple carbon sources. This study is also the first to demonstrate that dispersal of P. aeruginosa correlates with a specific dispersal phenotype.

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.

The initial microbial colonization of tooth surfaces is a repeatable and selective process, with certain bacterial species predominating in the nascent biofilm. Characterization of the initial microflora is the first step in understanding interactions among community members that shape ensuing biofilm development. Using molecular methods and a retrievable enamel chip model, we characterized the microbial diversity of early dental biofilms in three subjects. A total of 531 16S rRNA gene sequences were analyzed, and 97 distinct phylotypes were identified. Microbial community composition was shown to be statistically different among subjects. In all subjects, however, 4-h and 8-h communities were dominated by Streptococcus spp. belonging to the Streptococcus oralis/Streptococcus mitis group. Other frequently observed genera (comprising at least 5% of clone sequences in at least one of the six clone libraries) were Actinomyces, Gemella, Granulicatella, Neisseria, Prevotella, Rothia, and Veillonella. Fluorescence in situ hybridization (FISH) confirmed that the proportion of Streptococcus sp. sequences in the clone libraries coincided with the proportion of streptococcus probe-positive organisms on the chip. FISH also revealed that, in the undisturbed plaque, not only Streptococcus spp. but also the rarer Prevotella spp. were usually seen in small multigeneric clusters of cells. This study shows that the initial dental plaque community of each subject is unique in terms of diversity and composition. Repetitive and distinctive community composition within subjects suggests that the spatiotemporal interactions and ecological shifts that accompany biofilm maturation also occur in a subject-dependent manner.More than 700 different bacterial phylotypes are found in the oral cavity, as determined by 16S rRNA gene sequencing (1). The initial colonizers of tooth surfaces are a specific subset of the oral microflora (24). Of these bacteria, those that colonize the clean enamel surface independently of other bacteria possess mechanisms for attachment to the acquired salivary pellicle covering the enamel (32) and the ability to metabolize salivary components as the sole nutritional source (27). Alternatively, some bacterial species participate in consortia that are able to attach to enamel and establish as an initial community requiring metabolic interactions among their members (18).Several studies have identified streptococci as the predominant colonizers of early enamel biofilms (17, 24). Nyvad and Kilian (24) characterized the cultivable microflora colonizing enamel pieces exposed to the oral cavity. Streptococci were shown to compose about 63% (mean value of samples from four individuals) of bacteria isolated after 4 h of plaque formation and 86% of bacteria isolated after 8 h. A variety of other bacteria such as veillonellae and actinomyces were also reported to be present. However, this study was performed at a time when rapid PCR-based taxonomic characterization of bacterial communities was not available. As a consequenc...

Nisin is a bacteriocin produced by a group of Gram-positive bacteria that belongs to Lactococcus and Streptococcus species. Nisin is classified as a Type A (I) lantibiotic that is synthesized from mRNA and the translated peptide contains several unusual amino acids due to post-translational modifications. Over the past few decades, nisin has been used widely as a food biopreservative. Since then, many natural and genetically modified variants of nisin have been identified and studied for their unique antimicrobial properties. Nisin is an FDA approved and GRAS (generally regarded as safe) peptide with recognized potential for clinical use. Over the past two decades the application of nisin has been extended to biomedical fields. Studies have reported that nisin can prevent the growth of drug-resistant bacterial strains, such as methicillin resistant Staphylococcus aureus, Streptococcus pneumoniae, Enterococci and Clostridium difficile. Nisin has now been shown to have antimicrobial activity against both Gram-positive and Gram-negative disease-associated pathogens. Nisin has been reported to have anti-biofilm properties and can work synergistically in combination with conventional therapeutic drugs. In addition, like host defense peptides, nisin may activate the adaptive immune response and have an immunomodulatory role. Increasing evidence indicates that nisin can influence the growth of tumors and exhibit selective cytotoxicity towards cancer cells. Collectively, the application of nisin has advanced beyond its role as a food biopreservative. Thus, this review will describe and compare studies on nisin and provide insight into its future biomedical applications.

Summary4,5-dihydroxy-2,3-pentanedione (DPD), a product of the LuxS enzyme in the catabolism of S -ribosylhomocysteine, spontaneously cyclizes to form autoinducer 2 (AI-2). AI-2 is proposed to be a universal signal molecule mediating interspecies communication among bacteria. We show that mutualistic and abundant biofilm growth in flowing saliva of two human oral commensal bacteria, Actinomyces naeslundii T14V and Streptococcus oralis 34, is dependent upon production of AI-2 by S. oralis 34. A luxS mutant of S. oralis 34 was constructed which did not produce AI-2. Unlike wild-type dual-species biofilms, A. naeslundii T14V and an S. oralis 34 luxS mutant did not exhibit mutualism and generated only sparse biofilms which contained a 10-fold lower biomass of each species. Restoration of AI-2 levels by genetic or chemical (synthetic AI-2 in the form of DPD) complementation re-established the mutualistic growth and high biomass characteristic for the wildtype dual-species biofilm. Furthermore, an optimal concentration of DPD was determined, above and below which biofilm formation was suppressed. The optimal concentration was 100-fold lower than the detection limit of the currently accepted AI-2 assay. Thus, AI-2 acts as an interspecies signal and its concentration is critical for mutualism between two species of oral bacteria grown under conditions that are representative of the human oral cavity.

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