Growth of Nitrobacter by dissimilatoric nitrate reduction

Abstract Eight strains of the genus Nitrobacter grew under anaerobic conditions in the presence of nitrate. The growth was inhibited by nitrate concentrations above 0.5 mM. By a special culture technique inhibition caused by nitrite was abolished. Nitrate oxidizing cells grew in gas tight culture flasks as a biofilm on a gas-permeable silicone tubing. The biofilm allowed nitrate-reducing cells to grow at a low nitrite concentration. These cells grew either actively motile in the anaerobic medium, or in anaerobic zones of the biofilm. They produced nitrite and ammonia. Nitrogen balance calculations established a loss of inorganic nitrogen for 5 of 8 strains. This implies that nitrate-reducing cells produced furthermore volatile nitrogen compounds. N₂O was detected by gas chromatography.     

Interactions between plasma proteins and pulmonary surfactant: pulsating bubble studies

The influence of human albumin, alpha-globulin, and fibrinogen on the actions of porcine pulmonary surfactant in a pulsating bubble surfactometer has been investigated. All three proteins detracted from the ability of the surfactant to adsorb to the air-water interface. The proteins also reduced the ability of surfactant to lower the opening pressures of bubbles cycling between different sizes in suspensions of surfactant. This was equivalent to restricting the ability of the surfactant to achieve low surface tension during compression of the surface. Of the three proteins, globulin competed most effectively with surfactant during the adsorption process, and albumin competed the least effectively. The proteins also may have interfered with the processes of surface refinement, which usually yields a monolayer enriched enough in dipalmitoyl phosphatidylcholine to achieve very low surface tension (very low opening pressures in the bubbles). Of the three proteins tested, albumin was least deleterious to surface refining whereas globulin and fibrinogen appeared to be about equally detrimental to the process.     

Reconstituted skin in culture:a simple method with optimal differentiation

Human skin is a unique organ, which can be reconstituted in vitro and represents an interesting system for studying cell proliferation and differentiation. A simple technique for producing reconstituted skin with optimal epidermal differentiation is described and characterized. A 4-mm punch biopsy of normal human skin is deposited on the epidermal side of mortified de-epidermized human dermis maintained at the air-liquid interface with a metallic support. The culture medium contains insulin, epidermal growth factor (EGF), cholera toxin, hydrocortisone, penicillin/streptomycin and fungizone. A well-differentiated epidermis develops within 15 days. Morphological and ultrastructural studies show a neoepidermis resembling normal skin. Differentiation markers such as involucrin, filaggrin, and various cytokeratins detected with pancytokeratin antibody are present and confirm this resemblance. The keratin profile is comparable to that observed in other skin culture models. A basement-membrane-like structure is reconstituted with hemidesmosomes and anchoring-filament formation. Bullous pemphigoid (BP) antigen is observed at the dermo-epidermal junction after 21 days of culture. Moreover, both dermal substrates and punch biopsies can be kept frozen for long-term storage, with little or no loss of epidermal growth kinetics and morphology. This skin culture technique is rapid, simple, economical and reproducible. Characterization has here shown high-quality epidermal differentiation. Scientists interested in epidermal in vitro studies should take interest in all these advantages.     

Appearance of alpha-smooth muscle actin in human eye lens cells of anterior capsular cataract and in cultured bovine lens-forming cells

Using light and electron-microscopic immunolocalization techniques, and gel electrophoresis combined with immunoblotting, we have examined the expression of cytoskeletal proteins in normal human fetal, child and adult lenses, in human anterior capsular cataract and in bovine lens cells in vivo and in vitro. In this report, we focus our observations on the pattern of actin-isoform expression during normal and pathological situations in vivo and culture conditions. We have noted that cells of developing and mature human lenses as well as bovine lens cells in situ contain only beta- and gamma-actins. In contrast, alpha-smooth muscle (alpha-sm) actin, an isoform typical of smooth muscle differentiation, was demonstrated in bovine lens cells at different times of culture. Moreover, the multilayered cells observed in the subcapsular zone of human anterior capsular cataract were characterized by the presence of alpha-sm actin. Thus, extensive changes in actin-isoform expression take place in lens cells growing in culture and may also occur during cataractogenesis. The biological meaning of the appearance of a marker of myoid differentiation in the ectodermally derived lens-forming cells is discussed.     

Specificity of binding to four-way junctions in DNA by bacteriophage T7 endonuclease I.

T7 endonuclease I binds specifically to four-way junctions in duplex DNA and promotes their resolution into linear duplexes. Under conditions in which the nuclease activity is blocked by the absence of divalent cations, the enzyme forms a distinct protein-DNA complex with the junction, as detected by gel retardation and filter binding assays. The formation of this complex is structure-specific and contrasts with the short-lived binding complexes formed on linear duplex DNA. The binding complex between T7 endonuclease I and a synthetic Holliday junction analog has been probed with hydroxyl radicals. The results indicate that the nuclease binds all four strands about the junction point.     

The haplotype distribution of the ΔF508 mutation in cystic fibrosis families in Scotland

Summary The gene defective in cystic fibrosis (CF) has recently been isolated and the major mutation identified. The haplotype distribution of this mutation (ΔF508) has been determined for 215 CF chromosomes in the Scottish population. ΔF508 represents 73% of all CF mutations in this group. There remains considerable linkage disequilibrium between XV2c and KM19 and other mutations in the CF gene.     

Resistance to human serum of gonococci in urethral exudates is reduced by neuraminidase

Gonococci examined directly from urethral exudates are resistant to killing by human serum, but most strains become susceptible on subculture. Previous work with gonococci grown in vitro indicates that resistance in vivo is due to sialylation of gonococcal lipopolysaccharide (LPS) by a host factor, cytidine 5'-monophospho-N-acetylneuraminic acid (CMP-NANA) or a related compound present in urogenital secretions and blood cells including phagocytes, which exude during inflammation. This sialylation inhibits the reaction between bactericidal IgM in serum and its target LPS sites. Here, we confirm the indication by using gonococci grown in vivo. Crucial to the above conclusions was the marked reduction of CMP-NANA-conferred serum resistance when gonococci were treated with neuraminidase to remove sialyl groups from their LPS. We now show that the serum resistance of gonococci in urethral exudates was reduced by treatment with neuraminidase from more than 95% (calculated in relation to controls incubated with heated serum) to 2-11% according to sample and incubation time. Subculture of the gonococci also reduced resistance to 9-11% but resistance was restored to more than 95% by incubation with CMP-NANA. This work is the culmination of an investigation that underlines the need to identify specific host factors and the virulence determinants they induce in vivo in future studies of pathogenicity.