Identification and characterization of the S-layer formed on the sheath of Thiothrix nivea.

Thiothrix nivea is a filamentous sulfur-oxidizing bacterium common in activated sludge and its filament is covered with a polysaccharide layer called sheath. In this study, we found that T. nivea aggregates under acidic conditions. A hexagonal lattice pattern, a typical morphological feature of proteinaceous S-layers, was newly observed on the surface of the sheath by transmission electron microscopy. The pattern and the acid-dependent aggregation were not observed in T. fructosivorans, a relative sheath-forming bacterium of T. nivea. The putative S-layer of T. nivea was detached by washing with unbuffered tris(hydroxymethyl)aminomethane base (Tris) solution and a protein of 160 kDa was detected by electrophoresis. Based on partial amino acid sequences of the protein, its structural gene was identified. The gene encodes an acidic protein which has a putative secretion signal and a Ca2+-binding domain. The protein was solubilized with urea followed by dialysis in the presence of calcium. A hexagonal lattice pattern was observed in the aggregates formed during dialysis, revealing that the protein is responsible for S-layer formation. Biosorption ability of copper, zinc, and cadmium onto the T. nivea filament decreased upon pretreatment with Tris, demonstrating that the S-layer was involved in metal adsorption. Moreover, aggregation of Escherichia coli was promoted by acidification in the presence of the S-layer protein, suggesting that the protein is potentially applicable as an acid-driven flocculant for other bacteria.

Enzymatic degradation of ß-1,4-linked N-acetylglucosaminoglucan prepared from Thiothrix nivea.

Thiothrix nivea is a filamentous sulfur-oxidizing bacterium commonly found in activated sludge. The filament of this bacterium is covered with a sheath. The sheath is an assemblage of macromolecular glucosaminoglucan (GG), [4)-ß-d-GlcN-(1 → 4)-ß-d-Glc-(1 → ]n, modified with an unidentified deoxy-sugar at position 3 of Glc. GG was obtained by dialysis after the partial hydrolysis of the sheath. The GG hydrogel was prepared by drying a GG solution. Then, the hydrogel was N-acetylated to prepare a stable hydrogel of N-acetylglucosaminoglucan (NGG), [4)-ß-d-GlcNAc-(1 → 4)-ß-d-Glc-(1 → ]n. The NGG hydrogel was stable in phosphate buffer but was disrupted by lysozyme addition, suggesting that NGG is susceptible to lysozyme degradation and has potential for medical use. The GG solution was N-acetylated to prepare a NGG suspension to confirm enzymatic degradation. The turbidity of the NGG suspension was decreased by lysozyme addition. Sugars released in the reaction mixture were derivatized with 4-aminobenzoic acid ethyl ester (ABEE) followed by HPLC analysis. Two major derivatives were detected, and their concentration was increased in reverse proportion to the turbidity of the reaction mixture. The derivatives were identified as GlcNAc-Glc-GlcNAc-Glc-ABEE and GlcNAc-Glc-ABEE by mass spectrometry. Consequently, NGG was found to be degraded by lysozyme via a mechanism similar to that of chitin degradation.

Detection of antibodies against Paracoccidioides brasiliensis in free-range domestic pigs (Sus scrofa).

Paracoccidioidomycosis, caused by the thermodimorphic fungus Paracoccidioides brasiliensis, is a human systemic mycosis prevalent in Latin America. Paracoccidioidomycosis affects mainly male rural workers, causing granulomatous lesions in several organs such as the lungs, liver and spleen. The participation of other animal species in the fungus epidemiology is not well understood. The objective of this study was to evaluate the infection of free-range domestic pigs by P. brasiliensis. Serum samples from 106 pigs were analyzed by ELISA and the immunodiffusion test, using P. brasiliensis gp43 and exoantigen as antigens, respectively. The overall positivity to gp43 in ELISA was 37.7 %, although no reactivity was observed in the immunodiffusion test and nor was P. brasiliensis detected in tissue samples (spleen, lung, liver and lymph nodes) from slaughtered animals submitted to culture, histopathological examination and PCR analysis. Five pigs seronegative to gp43 were exposed to natural infection by P. brasiliensis, and all animals seroconverted 3 months after exposure. The results suggest that free-range pigs are frequently infected with P. brasiliensis but are resistant to disease development. This is the first report of paracoccidioidomycosis in pigs.

Participação de células T regulatórias (Tregs) na imunopatogênese da infecção pelo vírus da imunodeficiência humana 1 (HIV-1) / Regulatory T cells participation in the infection immunopathogenesis by the Human Immunodeficiency Vírus

A sobrevivência de pacientes infectados pelo vírus da imunodeficiência humana (HIV-1) é relacionada à prevenção e ao tratamento eficaz de infecções oportunistas. É conhecido que os principais parâmetros para avaliar a progressão da doença causada pelo HIV-1 são contagem de células T CD4+ e carga viral do HIV-1. Células T regulatórias têm sido foco de intensas investigações dentro do sistema imunológico como também na patogênese de diversas doenças. Sabe-se que as células T reguladoras (Tregs) CD4+CD25+FoxP3+ atuam na modulação da ativação imune, funcionando como mediadores críticos da homeostasia imune e da auto-tolerância. Além disso, recentes estudos têm demonstrado que as células Tregs não se limitam à prevenção de auto-imunidade, mas são importantes no controle todas as formas de respostas imunes no contexto de inflamação, infecção, alergia, transplantes e imunidade tumoral. Muitos autores têm identificado as Tregs como células efetoras benéficas no contexto da AIDS, porém há discordância. Tregs podem sustentar importante função na imunopatologia da infecção pelo HIV devido a atividade supressora sobre ativação celular e função efetora. Neste contexto, esta revisão aborda os aspectos moleculares e imunológicos das Tregs no sistema HIV.

The survival of patients infected with human immunodeficiency virus (HIV-1) is related to the prevention and effective treatment of opportunistic infections. It is known that the main parameters to evaluate the progression of disease caused by HIV-1 is the counting of CD4 + T cells and viral load of HIV-1. Regulatory T cells has been considered the focus of intense research within the immune system as well as in the pathogenesis of several diseases. Natural regulatory T cells (Tregs) CD4+CD25+ act in the modulation of immune activation, functioning as critical mediators of immune homeostasis and self-tolerance. Furthermore, recent studies has shown that the function of Tregs cells is not limited to the prevention of autoimmunity, but is also important to control all forms of immune responses in the context of inflammation, infection, allergy, transplantation and tumor immunity. Many authors have identified Tregs as beneficial effector cells in the context of AIDS, but other researchers disagree. Tregs can exert an important role in the immunopathology of HIV infection due to the suppressor activity on cellular activation and effector function. Thus, this review discusses the molecular and immunological aspects of Tregs in the HIV system.