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Volume 164,
Issue 8,
2018
Volume 164, Issue 8, 2018

- Editorial
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- Microbe Profile
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Microbe Profile: Aspergillus fumigatus: a saprotrophic and opportunistic fungal pathogen
More LessAspergillus fumigatus is a saprotrophic fungus that continuously disseminates spores (conidia) into the environment. It is also the most common and opportunistic aerial fungal pathogen, causing allergic and chronic lung pathologies including the fatal invasive aspergillosis in immunocompromised patients. The pathobiology of aspergillosis is complex and depends on the competence of the host immune system. Moreover, A. fumigatus has become a model to study unique features of fungi. This includes the fungal cell wall, which not only acts as a rigid skeleton for protection against hostile environments but also plays significant roles during infection by manipulating the host immune response.
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- Host-Microbe Interaction
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Cell-wall dyes interfere with Cryptococcus neoformans melanin deposition
More LessMelanization is an intrinsic characteristic of many fungal species, but details of this process are poorly understood because melanins are notoriously difficult pigments to study. While studying the binding of cell-wall dyes, Eosin Y or Uvitex, to melanized and non-melanized Cryptococcus neoformans cells we noted that melanization leads to reduced fluorescence intensity, suggesting that melanin interfered with dye binding to the cell wall. The growth of C. neoformans in melanizing conditions with either of the cell-wall dyes resulted in an increase in supernatant-associated melanin, consistent with blockage of melanin attachment to the cell wall. This effect provided the opportunity to characterize melanin released into culture supernatants. Released melanin particles appeared mostly as networked structures having dimensions consistent with previously described extracellular vesicles. Hence, dye binding to the cell wall created conditions that resembled the ‘leaky melanin’ phenotype described for certain cell-wall mutants. In agreement with earlier studies on fungal melanins biosynthesis, our observations are supportive of a model whereby C. neoformans melanization proceeds by the attachment of melanin nanoparticles to the cell wall through chitin, chitosan, and various glucans.
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Evaluation of a novel outer membrane surface-exposed protein, LIC13341 of Leptospira, as an adhesin and serodiagnostic candidate marker for leptospirosis
The outer membrane proteins of the pathogen are targeted to understand host–pathogen interactions and are central to the development of diagnostics. We report that Leptospira interrogans serovar Copenhageni strain Fiocruz L1-130 contains a gene LIC13341 that encodes a conserved outer membrane/periplasmic lipoprotein. The gene LIC13341 was cloned into expression vector pET28a and the recombinant LIC13341 (r-LIC13341) protein was purified from Escherichia coli BL21 (DE3) using affinity chromatography. The secondary structure of the purified r-LIC13341 protein featured a typical β-strand when observed by circular dichroism spectroscopy. Immunoblotting using antibodies raised against r-LIC13341 in BALB/c mice can detect LIC13341 expression in the Leptospira lysates and suggested that antigen LIC13341 is immunogenic. Phase separation and protease assays determined that LIC13341 is a surface-exposed outer membrane protein of Leptospira. The r-LIC13341 can bind to a wide spectrum of host extracellular matrices (ECMs). The specific adherence of Leptospira to laminin and hyaluronic acid of the ECM was competitively inhibited in the presence of r-LIC13341. The enzyme-linked immunosorbent assay and immunoblot performed using human or bovine leptospirosis serum (n=50) recognized r-LIC13341, suggesting that LIC13341 is expressed in diverse hosts during Leptospira infection. Thus, the present finding suggests that the Leptospira LIC13341 antigen is a versatile outer membrane adhesin of diagnostic importance.
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Intergenic evolution during host adaptation increases expression of the metallophore pseudopaline in Pseudomonas aeruginosa
Regulating intracellular levels of biological metal ions is essential for all bacterial species, as they are needed for virulence and a range of metabolic processes. Zinc is the second most abundant metal ion in Pseudomonas aeruginosa, but little is known about its regulation. Recent studies have identified a novel operon, zrmABCD (also called cntOLMI), encoding a metallophore system (pseudopaline) involved in zinc acquisition. Expression of this operon has been implicated in human infections and is regulated by the transcriptional regulator Zur (Zn2+ uptake regulator). In this study, we show that the intergenic promoter region in front of zrmABCD is a target for recurrent adaptive mutations during chronic infection of cystic fibrosis (CF) patients. We characterize the inter- and intraclonal sequence polymorphisms found in the promoter region of the metallophore system and find that most alterations increase promoter activity. One of the evolved promoters displays a more than 10-fold increase compared to the ancestral strain due to the combined effect of an altered binding site of Zur and changes to the RpoD-binding motif. This specific evolved promoter responds differently to changes in metal ion concentrations in chelated medium. We have previously shown that P. aeruginosa evolves toward iron acquisition from haemoglobin during long-term CF infections. We hereby provide the second example of adaptive mutations targeting intergenic regions that affect metal ion uptake systems during CF infections, and the first involving zinc uptake. Our results suggest that the scarcity of metal ions (including iron and zinc) is an important evolutionary driver in CF host adaptation.
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- Physiology and Metabolism
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Comprehensive screening of antimicrobials to control phytoplasma diseases using an in vitro plant–phytoplasma co-culture system
Phytoplasmas are plant-pathogenic bacteria that infect many important crops and cause serious economic losses worldwide. However, owing to an inability to culture phytoplasmas, screening of antimicrobials on media is difficult. The only antimicrobials being used to control phytoplasmas are tetracycline-class antibiotics. In this study, we developed an accurate and efficient screening method to evaluate the effects of antimicrobials using an in vitro plant–phytoplasma co-culture system. We tested 40 antimicrobials, in addition to tetracycline, and four of these (doxycycline, chloramphenicol, thiamphenicol and rifampicin) decreased the accumulation of ‘Candidatus (Ca.) Phytoplasma asteris'. The phytoplasma was eliminated from infected plants by the application of both tetracycline and rifampicin. We also compared nucleotide sequences of rRNAs and amino acid sequences of proteins targeted by antimicrobials between phytoplasmas and other bacteria. Since antimicrobial target sequences were conserved among various phytoplasma species, the antimicrobials that decreased accumulation of ‘Ca. P. asteris' may also have been effective against other phytoplasma species. These approaches will provide new strategies for phytoplasma disease management.
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Helicobacter pylori nickel storage proteins: recognition and modulation of diverse metabolic targets
More LessNickel metabolism and trafficking in Helicobacter pylori is complex, perhaps more so than in any other pathogen. Along with nickel enzymes and their associated nickel-binding maturation machinery, H. pylori contains nickel storage proteins, Hpn and Hpnl. Through a combined crosslinking and enrichment approach, we show that Hpn/Hpnl interact with a wide array of partners; over 100 proteins were captured, including known nickel-enzyme maturation proteins, and other proteins outside known H. pylori nickel-associated proteins. The crosslinker binds to exposed amines, but there was no correlation between lysine content and the pulldown abundance of captured proteins. Phenotypic characterization of mutant strains (Δhpn, Δhpnl, or ΔhpnΔhpnl) was used to explore interactions. Nickel deprivation affected the hydrogenase activity of the ΔhpnΔhpnl strain much more severely than the wild-type (WT), whereas the activities of the single mutants were similar to WT. Leucyl aminopeptidase activity was affected in opposite ways in the mutant strains: Δhpn had a threefold decrease, while Δhpnl had a sevenfold increase, compared to the parent. Similar mutant strain analysis supported Hpn and Hpnl acting synergistically to suppress aliphatic amidase activity in a nickel-dependent manner. Recombinant amidase could bind a variety of divalent metals. Amidase activity was greatest in the mutant strains and was inhibited by exogenous nickel. The addition of pure storage protein to extracts from the mutants only restored the suppression of amidase activity for the mutant strain lacking that protein; both storage proteins are needed for amidase suppression. These results suggest that Hpn and Hpnl play more diverse roles than previously thought.
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