The well-coordinated linkage between acidogenicity and aciduricity via insoluble glucans on the surface of Streptococcus mutans.

Streptococcus mutans is considered the principal cariogenic bacterium for dental caries. Despite the recognition of their importance for cariogenesis, the possible coordination among S. mutans' main virulence factors, including glucan production, acidogenicity and aciduricity, has been less well studied. In the present study, using S. mutans strains with surface-displayed pH-sensitive pHluorin, we revealed sucrose availability- and Gtf functionality-dependent proton accumulation on S. mutans surface. Consistent with this, using a pH-sensitive dye, we demonstrated that both in vivo cell-produced and in vitro enzymatically synthesized insoluble glucans displayed proton-concentrating ability. Global transcriptomics revealed proton accumulation triggers the up-regulation of genes encoding functions involved in acid tolerance response in a glucan-dependent manner. Our data suggested that this proton enrichment around S. mutans could pre-condition the bacterium for acid-stress. Consistent with this hypothesis, we found S. mutans strains defective in glucan production were more acid sensitive. Our study revealed for the first time that insoluble glucans is likely an essential factor linking acidogenicity with aciduricity. The coordination of these key virulence factors could provide new insights on how S. mutans may have become a major cariogenic pathogen

Type IV pilus of Myxococcus xanthus is a motility apparatus controlled by the frz chemosensory system

AbstractAlthough flagella are the best-understood means of locomotion in bacteria [1], other bacterial motility mechanisms must exist as many diverse groups of bacteria move without the aid of flagella [2–4]. One unusual structure that may contribute to motility is the type IV pilus [5,6]. Genetic evidence indicates that type IV pili are required for social gliding motility (S-motility) in Myxococcus, and twitching motility in Pseudomonas and Neisseria[6,7]. It is thought that type IV pili may retract or rotate to bring about cellular motility [6,8], but there is no direct evidence for the role of pili in cell movements. Here, using a tethering assay, we obtained evidence that the type IV pilus of Myxococcus xanthus functions as a motility apparatus. Pili were required for M. xanthus cells to adhere to solid surfaces and to generate cellular movement using S-motility. Tethered cells were released from the surface at intervals corresponding to the reversal frequency of wild-type cells when gliding on a solid surface. Mutants defective in the control of directional movements and cellular reversals (frz mutants) showed altered patterns of adherence that correlate reversal frequencies with tethering. The behavior of the tethered cells was consistent with a model in which the pili are extruded from one cell pole, adhere to a surface, and then retract, pulling the cell in the direction of the adhering pili. Cellular reversals would result from the sites of pili extrusion switching from one cell pole to another and are controlled by the frz chemosensory system

Mapping the tail fiber as the receptor binding protein responsible for differential host specificity of Pseudomonas aeruginosa bacteriophages PaP1 and JG004.

The first step in bacteriophage infection is recognition and binding to the host receptor, which is mediated by the phage receptor binding protein (RBP). Different RBPs can lead to differential host specificity. In many bacteriophages, such as Escherichia coli and Lactococcal phages, RBPs have been identified as the tail fiber or protruding baseplate proteins. However, the tail fiber-dependent host specificity in Pseudomonas aeruginosa phages has not been well studied. This study aimed to identify and investigate the binding specificity of the RBP of P. aeruginosa phages PaP1 and JG004. These two phages share high DNA sequence homology but exhibit different host specificities. A spontaneous mutant phage was isolated and exhibited broader host range compared with the parental phage JG004. Sequencing of its putative tail fiber and baseplate region indicated a single point mutation in ORF84 (a putative tail fiber gene), which resulted in the replacement of a positively charged lysine (K) by an uncharged asparagine (N). We further demonstrated that the replacement of the tail fiber gene (ORF69) of PaP1 with the corresponding gene from phage JG004 resulted in a recombinant phage that displayed altered host specificity. Our study revealed the tail fiber-dependent host specificity in P. aeruginosa phages and provided an effective tool for its alteration. These contributions may have potential value in phage therapy

The ‘CheA’ and ‘CheY’ domains of Myxococcus xanthus FrzE function independently in vitro as an autokinase and a phosphate acceptor, respectively

AbstractFrzE is a chemotaxis protein in Myxococcus xanthus which has sequence homology to two different chemotaxis proteins of enteric bacteria, CheA (autokinase) and CheY (phosphate acceptor) [Proc. Natl. Acad. Sci. USA 87 (1990) 5898–5902]. It was also shown that a recombinant FrzE protein was autophosphorylated when incubated in the presence of ATP and Mn2+ [J. Bacteriol. 172 (1990) 6661–6668]. In this study, we further investigated the biochemical properties of FrzE. Two recombinant proteins were produced: one containing only the ‘CheA’ domain of FrzE and the second only the ‘CheY’ domain. The CheA domain polypeptide contained the autokinase activity which was absent from the CheY domain polypeptide. The phosphorylated CheA domain polypeptide as well as the intact FrzE protein were able to transfer phosphate groups to the CheY domain peptide. These results indicate that FrzE has structural as well as functional homologies to CheA and CheY in a single polypeptide

Managing Denture Biofilm Related Diseases

The oral cavity harbors more than 700 microbial species and is one of the most complex ecosystems ever described. While the majority of these microbes are considered commensal, some of them are responsible for oral infectious diseases such as dental caries, periodontitis, halitosis and stomatitis. The advancement of modern science has greatly furthered our understanding of oral microbes and their roles in host health and disease. It has also led to the development of new tools for early detection, effective treatment, and prevention of oral microbial infections. This perspective provides a general understanding of oral microbiology, and its clinical relationship to oral infectious diseases, with a specific focus on denture-related microbial infections. The perspective also discusses the potential for developing innovative interventions for managing denture-related disease based on recent advances in our understanding of oral microbiology and denture-associated biofilms

DNA builds and strengthens the extracellular matrix in Myxococcus xanthus biofilms by interacting with exopolysaccharides.

One intriguing discovery in modern microbiology is the extensive presence of extracellular DNA (eDNA) within biofilms of various bacterial species. Although several biological functions have been suggested for eDNA, including involvement in biofilm formation, the detailed mechanism of eDNA integration into biofilm architecture is still poorly understood. In the biofilms formed by Myxococcus xanthus, a Gram-negative soil bacterium with complex morphogenesis and social behaviors, DNA was found within both extracted and native extracellular matrices (ECM). Further examination revealed that these eDNA molecules formed well organized structures that were similar in appearance to the organization of exopolysaccharides (EPS) in ECM. Biochemical and image analyses confirmed that eDNA bound to and colocalized with EPS within the ECM of starvation biofilms and fruiting bodies. In addition, ECM containing eDNA exhibited greater physical strength and biological stress resistance compared to DNase I treated ECM. Taken together, these findings demonstrate that DNA interacts with EPS and strengthens biofilm structures in M. xanthus