1887

Microbiology Society logo - Volume 152, Issue 10, 2006

Volume 152, Issue 10

Volume 152, Issue 10, 2006

  • Pathogens And Pathogenicity

      • Significant passive protective effect against anthrax by antibody to inactivated spores that lack two virulence plasmids

        https://doi.org/10.1099/mic.0.28788-0

        The protective-antigen (PA)-based cell-free vaccine is the only vaccine licensed for use against infection in humans. Although the PA shows strong immunogenicity, the capsule or spore-associated somatic antigens may be important as additional vaccine targets for full protection against anthrax. In this study, the protective effect of spore-associated antigens against infection was determined. Rabbits were immunized with formalin-fixed spores of a non-toxigenic unencapsulated strain that lacked the two virulence plasmids pXO1 and pXO2, and the protective effects of the immune antibody were evaluated. Immunostaining and Western blot analysis revealed that the anti- (anti-BA)-spore IgG specifically bound to the surface of spores or endospores of , but not to vegetative cells, or closely related species, such as , and . Passively transferred anti-BA-spore IgG protected mice from intraperitoneal challenge with a lethal dose of fully virulent spores, and increased the survival rate in a dose-dependent manner. Pre-incubation of spores with antibody also reduced their infectivity in a dose-dependent manner. The number of bacteria (c.f.u.) in spleens and livers of infected mice was significantly lower in antibody-treated mice than in untreated mice. Treatment with anti-BA-spore IgG also inhibited the germination of spores in J774.1 macrophages, suggesting that opsonization of spores promotes phagocytosis and subsequent killing by macrophages. These results indicate the usefulness of spore surface antigens as vaccine targets. In combination with major virulence factors such as the PA, spore-associated antigens may offer a safer and more effective multicomponent vaccine for infection.

    • The vesicle transport protein Vac1p is required for virulence of

      https://doi.org/10.1099/mic.0.29115-0

      The putative vesicle transport protein Vac1p of the human pathogenic yeast plays an important role in virulence. To determine the cellular functions of Vac1p, a null mutant was generated by sequential disruption of both alleles. The null mutant strain showed defective endosomal vesicle transport, demonstrating a role of Vac1p in protein transport to the vacuole. Vac1p also contributes to resistance to metal ions, as the null mutant strain was hypersensitive to Cu, Zn and Ni. In addition, the loss of Vac1p affected several virulence factors of . In particular, the null mutant strain showed defective hyphal growth, even when hyphal formation was induced via different pathways. Furthermore, Vac1p affects chlamydospore formation, adherence to human vaginal epithelial cells, and the secretion of aspartyl proteinases (Saps). Avirulence in a mouse model of systemic infection of the null mutant strongly suggests that Vac1p of is essential for pathogenicity. In summary, the Vac1p protein is required for several cellular pathways, in particular those that control virulence and pathogenicity. Consequently, Vac1p is a novel and interesting target for antifungal drugs.

    • The locus positively regulates type 5 capsule via an -dependent pathway

      https://doi.org/10.1099/mic.0.29177-0

      Most clinical strains produce either type 5 or type 8 capsular polysaccharides. The production of these capsules is influenced by various environmental factors. To study the regulation of capsule, Tn transposon mutagenesis and transcriptional reporter gene fusion were employed to identify several putative regulatory loci that influenced capsule gene expression. One of these, the locus, was chosen for further analysis. Tn was found to insert within the coding region (near the translational start site of the gene). ArlR, along with ArlS, forms a two-component system that has been previously shown to affect autolysis and production of several secreted proteins. Phenotypic analyses of the -specific mutant and gene fusion analyses showed that activated capsule production at the transcriptional level. However, gel mobility shift assays did not support activation of the capsule genes by direct ArlR binding to the primary promoter region upstream of the operon. In contrast, it was found that activated , an activator for capsule production, whereas did not have a significant effect on . Genetic studies supported the notion that functions upstream of with respect to the regulation of capsule production, although gene fusion studies indicated that could also regulate capsule independently from . Collectively, the results suggest that positively regulates capsule production at the transcriptional level primarily through an -dependent pathway.

Top
  • Physiology

      • Nutrient regulation of oligopeptide transport in

        https://doi.org/10.1099/mic.0.29055-0

        Small peptides (2–5 amino acid residues) are transported into via two transport systems: PTR (eptide ansport) for di-/tripeptides and OPT (ligoeptide ransport) for oligopeptides of 4–5 amino acids in length. Although regulation of the PTR system has been studied in some detail, neither the regulation of the OPT family nor the environmental conditions under which family members are normally expressed have been well studied in . Using a reporter gene construct fused to 1 kb DNA from upstream of the genes and , which encode the two oligopeptide transporters, the relative expression levels of these genes were measured in a variety of environmental conditions. Uptake assays were also conducted to measure functional protein levels at the plasma membrane. It was found that was up-regulated in sulfur-free medium, and that Ptr3p and Ssy1p, proteins involved in regulating the di-/tripeptide transporter encoding gene via amino acid sensing, were required for expression in a sulfur-free environment. In contrast, as measured by response to toxic tetrapeptide and by real-time PCR, was not regulated through Cup9p, which is a repressor for expression, although Cup9p did repress expression. In addition, all of the 20 naturally occurring amino acids, except the sulfur-containing amino acids methionine and cysteine, up-regulated , with the greatest change in expression observed when cells were grown in sulfur-free medium. These data demonstrate that regulation of the OPT system has both similarities and differences to regulation of the PTR system, allowing the yeast cell to adapt its utilization of small peptides to various environmental conditions.

    • Glycerol, ethylene glycol and propanediol elicit pimaricin biosynthesis in the PI-factor-defective strain 287 and increase polyene production in several wild-type actinomycetes

      https://doi.org/10.1099/mic.0.28953-0

      Production of pimaricin by ATCC 27448 is elicited by the PI-factor, an autoinducer secreted by the producer strain during the rapid growth phase. Exogenous PI-factor restored pimaricin production in a mutant strain 287 defective in PI-factor biosynthesis. During purification of the PI-factor, a second pimaricin-inducing fraction different from PI-factor was isolated from the culture broth of wild-type ATCC 27448. After purification by HPLC and analysis by MS and NMR, this active fraction was shown to contain glycerol and lactic acid. Pure glycerol restored pimaricin production in liquid cultures of the autoinducer-defective 287 mutant. A similar effect was exerted by ethylene glycol, 1,2-propanediol and 1,3-propanediol but not by higher polyalcohols or by glycerol acetate or glycerol lactate esters. Glycerol stimulated (30–270 %) the production of six different polyene macrolide antibiotics by their respective producer strains. Addition of glycerol to the inducer-defective 287 strain restored pimaricin production but did not result in extracellular or intracellular accumulation of PI-factor. Exogenously added PI-factor was internalized by the cells in the presence of glycerol, and a mixture of both PI-factor and glycerol produced a slightly higher inducing effect on pimaricin production than PI-factor alone. In summary, glycerol, ethylene glycol and propanediol exert a bypass of the PI-factor inducing effect on pimaricin biosynthesis.

    • Identification and characterization of membrane transporters necessary for utilization of the siderophore pyridine-2,6-bis(thiocarboxylic acid) (PDTC)

      https://doi.org/10.1099/mic.0.29116-0

      The compound pyridine-2,6-bis(thiocarboxylic acid) (PDTC) is known to be produced and excreted by three strains of . Its reactivity includes the complete dechlorination of the environmental contaminant carbon tetrachloride. PDTC functions as a siderophore; however, roles as a ferric reductant and antimicrobial agent have also been proposed. PDTC function and regulation were further explored by characterizing the phenotypes of mutants in predicted membrane transporter genes. The functions of a predicted outer-membrane transporter (PdtK) and a predicted inner-membrane permease (PdtE) were examined in DSM 3601. Uptake of iron from Fe(III):PDTC, and bioutilization of PDTC in a chelated medium, were dependent upon PdtK and PdtE. Another strain of (KT2440), which lacks orthologues, showed growth inhibition by PDTC that could be relieved by introducing a plasmid containing KCPE. Transcriptional activation in response to exogenously added PDTC (25 μM) was unaltered by the K or E mutations; each mutant showed activation of a transcriptional reporter, indistinguishable from an isogenic PDTC utilization-proficient strain. The data demonstrate that PdtK and PdtE constitute a bipartite outer-membrane/inner-membrane transport system for iron acquisition from Fe(III):PDTC. Disruptions in this portion of the DSM 3601 gene cluster do not abolish PDTC-dependent transcriptional signalling.

Top
  • Plant-Microbe Interactions

      • Contribution of alginate and levan production to biofilm formation by

        https://doi.org/10.1099/mic.0.28875-0

        Exopolysaccharides (EPSs) play important roles in the attachment of bacterial cells to a surface and/or in building and maintaining the three-dimensional, complex structure of bacterial biofilms. To elucidate the spatial distribution and function of the EPSs levan and alginate during biofilm formation, biofilms of strains with different EPS patterns were compared. The mucoid strain PG4180.muc, which produces levan and alginate, and its levan- and/or alginate-deficient derivatives all formed biofilms in the wells of microtitre plates and in flow chambers. Confocal laser scanning microscopy with fluorescently labelled lectins was applied to investigate the spatial distribution of levan and an additional as yet unknown EPS in flow-chamber biofilms. Concanavalin A (ConA) bound specifically to levan and accumulated in cell-depleted voids in the centres of microcolonies and in blebs. No binding of ConA was observed in biofilms of the levan-deficient mutants or in wild-type biofilms grown in the absence of sucrose as confirmed by an enzyme-linked lectin-sorbent assay using peroxidase-linked ConA. Time-course studies revealed that expression of the levan-forming enzyme, levansucrase, occurred mainly during early exponential growth of both planktonic and sessile cells. Thus, accumulation of levan in biofilm voids hints to a function as a nutrient storage source for later stages of biofilm development. The presence of a third EPS besides levan and alginate was indicated by binding of the lectin from to a fibrous structure in biofilms of all derivatives. Production of the as yet uncharacterized additional EPS might be more important for biofilm formation than the syntheses of levan and alginate.

◄ 1 2
20 | 50 | 100 per page

Volumes and issues

Most cited Most Cited RSS feed

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error