1,721,111 research outputs found
Regulation of aerobic and anaerobic metabolism in facultative anaerobes: A role for cytochrome a<sub>1</sub>
No full textDespite extensive documentation, the regulatory effects of oxygen on protein synthesis are poorly understood. Oxygen either functions directly or indirectly, through changes in Eh or respiratory activity, or by interacting with a sensor molecule analogous to the lac repressor. Cytochrome a1, hitherto of unknown function in most bacteria, is proposed as the likely sensor
Immunogold and fluorescein immunolabelling of Legionella pneumophila within an aquatic biofilm visualized by using episcopic differential interference contrast microscopy
No full textBiofilms containing diverse microflora were developed in tap water on glass and polybutylene surfaces. Legionella pneumophila within the biofilms was labelled with monoclonal antibodies and visualized with immunogold or fluorescein isothiocyanate conjugates. Development of a differential interference contrast technique in an episcopic mode enabled simultaneous visualization of the total biofilm flora and gold-labelled legionellae. The legionellae occurred in microcolonies within the biofilm in the absence of amoebae, suggesting that the bacterial consortium was supplying sufficient nutrients to enable legionellae to grow extracellularly within the biofilm.</p
Effect of growth conditions on the involvement of cytochrome c in electron transport, proton translocation and ATP synthesis in the facultative methylotroph Pseudomonas AM1
No full textThe stoicheiometry of proton translocation, the amounts of cytochromes firmly bound to membranes, and cell yields with respect to succinate and O2 have been measured in the facultative methylotroph Pseudomonas AM1 and in the mutant lacking cytochrome c (mutant PCT76) during carbon-limited growth and carbon-excess growth. →H+/O ratios during endogenous respiration of about 4 were measured in wild-type bacteria grown in carbon-excess conditions, and in the mutant in all growth conditions. During methanol- or succinate-limited growth of wild-type bacteria the →H+/O ratio increased to about 6. Cell yields with respect to succinate and O2 were higher in wild-type than in the mutant lacking cytochrome c by an amount suggesting loss in the mutant of 30% of the ATP-generating capacity of wild-type bacteria. During carbon-limited growth on methanol or succinate some cytochrome c was tightly bound to bacterial membranes, whereas none was tightly bound in bacteria grown in batch-culture or in NH4+-limited conditions. It is proposed that the role of cytochrome c in Pseudomonas AM1 depends on growth conditions and hence on the ‘needs’ of the bacteria. During growth in carbon-excess conditions it is only required for methanol oxidation, mediating between methanol dehydrogenase and cytochrome a/a3. In these conditions oxidation of NADH and succinate by way of cytochrome b and cytochrome a/a3 occurs without the mediation of cytochrome c. This is the only route for oxidation of NADH and succinate in the cytochrome c-deficient mutant in all growth conditions. During carbon-limited growth the cytochrome c becomes bound to the membrane in such a way that it can mediate between cytochromes b and a/a3, hence becoming involved in proton translocation and ATP synthesis during NADH and succinate oxidation. An alternative possibility is that in wild-type bacteria the cytochrome c is always involved in electron transport, but that its involvement in measurable proton translocation only occurs in carbon-limited conditions
A simple artificial urine for the growth of urinary pathogens
No full text
A simple artificial urine medium (AUM) has been developed which provides conditions similar to that found in human urine. AUM solidified with agar enabled the recovery of a wide range of urease-positive and -negative urinary pathogens. Liquid AUM supported growth at concentrations of up to 10
8
cfu ml
-1
, as found in normal urine. Reproducible, steady-state growth also occurred over many generations in continuous culture. AUM was capable of forming crystals and encrustations resembling those found in natural urinary tract infections. The medium is a suitable replacement for normal urine for use in a wide range of experiments modelling the growth and attachment of urinary pathogens in the clinical environment.
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The presence of two cytochromes b in the facultative methylotroph Pseudomonas AM1
No full textTwo cytochromes b with absorption maxima at 555 and 562 nm and differing in their mid-point redox potentials are synthesized in Pseudomonas AM1 during growth on methanol or succinate in batch culture, or in NH4+-limited or carbon-limited continuous culture. Both cytochromes b were also present in a cytochrome c-deficient mutant in all growth conditions.</p
The relationship between proton translocation and cell yields in the facultative methylotroph Pseudomonas AMI and a mutant lacking cytochrome c [proceedings]
No full textInfluence of oxygen availability on physiology, verocytotoxin expression and adherence of Escherichia coli 0157
No full textA strain of Escherichia coli serotype 0157 was grown in steady state chemostat culture under aerobic, oxygen-limited and anaerobic conditions. The growth and metabolic efficiency of oxygen-limited and anaerobic cultures was impaired, with biomass yield and the molar growth yield for glucose, Y(glucose), reduced markedly in comparison with aerobic cultures. Steady state cells were typically short rods 2-3 μm long, and were encapsulated by a layer of extracellular material. The majority of cells were non-flagellated and fimbriae were not observed. Chemostat-grown cells were significantly more adhesive for HEp-2 monolayers than cells grown in aerobic batch culture. Furthermore, oxygen-limited and anaerobic cultures were significantly more adhesive for Hep-2 cells when compared with cells grown in aerobic chemostat culture, possibly reflecting increased pathogenicity associated with the induction of novel adhesins. Type 1 pill were not responsible for increased adherence. Verocytotoxins, VT1 and VT2, were expressed constitutively and were not influenced by oxygen availability. This study demonstrates that E. coli 0157 is a versatile micro-organism, which responds to environmental conditions likely to be encountered during infection by inducing a phenotype which is more adhesive for human epithelial cells
Correction: Inactivation of norovirus on dry copper alloy surfaces (PLoS ONE (2013) 8, 9 (e75017) DOI: 10.1371/journal.pone.0075017)
No full textDevelopment of the BIOLOG substrate utilization system for identification of Legionella spp
No full textThe genus Legionella consists of 51 serogroups comprising 34 species. Biochemical reactions and cell wall fatty acid and quinone analyses may confirm that an isolate is a Legionella sp. and indicate to which species it belongs, but DNA hybridization studies have been necessary for a definitive identification. Recently, the commercially available BIOLOG identification system has offered a standardized, easily reproducible system of substrate metabolism by bacteria resuspended in multiwell plates. A tetrazolium dye acts as an electron acceptor during the oxidation of the wide range of substrates and forms an irreversible, highly colored formazan when reduced. The 95 substrate wells are read rapidly with a conventional plate reader, and the results are donwloaded for comparison with a computer data base, allowing quick identification. The BIOLOG system's ability to test more diverse classes of substrates, including amino acids, peptides, carboxylic acids, and carbohydrates, was used in this study to establish a new data base and identify the asaccharolytic Legionella spp. In particular, Legionella pneumophila behaved as a microaerophile, and the fastest, most diverse metabolic activities occurred after the development of a low-oxygen incubation environment. Alternatively, bacteria could be successfully incubated in air when their concentration was double that recommended by the manufacturer. Similar results were obtained by using either Page's amoebal saline or distilled water as the resuspending and incubation medium. Type strains did not cross-identify with any of the strains already in the manufacturer's data base. The results indicate that this modified system has value in being able to identify Legionella isolates to the species level.</p
Study of microbial biofilms using light microscope techniques
No full textIn industrial ecosystems biofilms can cause severe problems in terms of obstruction, heat transfer, fluid dynamics and corrosion, and so detection of biofilms is therefore important to engineers. Visualisation of biofilms provides a rapid technique for the clarification of biofilm presence. Light microscopy has provided a mechanism of visualising the topology of the biofouling as well as the substrata, identifying particular micro-organisms and determining whether or not the bacteria are viable. Differential interference contrast enabled initial examination of opaque substrata such as copper or stainless steel prior to staining for discrimination of the microorganisms. Subsequent staining of the biofilm with fluorochromes such as acridine orange enhanced differentiation of the micro-organisms against the substrata. Biofilms on galvanised and stainless steel coupons from laboratory chemostat models were exhibited as a heterogeneous film representing a mosaic. This mosaic nature of the biofilm would aggravate localised corrosion by setting up concentration cells. Vital dyes which fluoresce when reduced by metabolising cells have been utilised to determine the viability of bacteria within biofilms on coupons from laboratory models, as well as industrial samples after microbial control measures have been instigated. The position of the waterborne human pathogen Legionella pneumophila has been identified within biofilms with the use of direct labelling probes. The light microscope was equipped with various fluorescent filter combination blocks to enable different strains to be used simultaneously and with the use of long working distance lenses the specimen are not compressed.</p
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