1,721,168 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 textNonculturable <i>Escherichia coli</i> O157 in horticultural compost
No full textFresh produce-associated outbreaks of the foodborne pathogen Escherichia coli O157 are responsible for a number of disease cases, hospitalizations and deaths. In many cases, the source of contamination can be linked to the growing media of the food, although pathogen detection is problematic in these complex soil ecosystems. In this study, direct quantitative real-time PCR without pre-enrichment was used to detect 310 copies of the Tir gene, using a primer sequence specific to E. coli O157, in horticultural compost purchased from a commercial supplier. The pathogen could not be cultured on selective media but was visualized using peptide nucleic acid fluorescence in situ hybridization and cell elongation viability assay, confirming the viability. Enumeration of elongated E. coli O157 determined that there were 205 live cells per gram of compost. The nonculturability and confirmation of viability of the pathogen indicates its viable but nonculturable (VBNC) status. The detection of VBNC foodborne pathogens in environmental samples challenges current understanding of the nature of foodborne pathogen contamination. </p
Continuous culture models to study pathogens in biofilms
No full textA multi-stage continuous culture apparatus has been constructed to model mono-species biofilms and high species diversity biofilm consortia found in clinical practice, the natural environment and the built environment. New artificial saliva and urine media were developed, and natural and treated potable waters obtained, for the defined, reproducible generation of the biofilms containing bacterial and protozoal pathogens on various hydroxyapatite, plastic, metal and paint-covered substrata over many months. Following several modifications to the design, each chemostat vessel, linked in series or parallel, consists of a titanium top plate containing a variety of insertion ports for the monitoring electrodes, and addition/removal of gases, media, effluent, pH and redox titrants, antibacterial agents and coupon substrata for biofilm generation. Each top plate is clamped to a 1 liter glass vessel, containing the culture medium, and mounted on a stirrer with a heater pad to facilitate external heating and stirring, controlling the shear rate across the immersed coupons. There are few internal parts to go wrong. The growth rate is controlled by continuous addition of medium to the planktonic and sessile phases of the cultures. These model systems are ideal for generating biofilms either aerobically or anaerobically, and containing microaerophilic or anaerobic species, even in highly aerated media
Comparison of polyvinyl chloride membrane electrodes sensitive to alkylphosphonium ions for the determination of the electrical difference (ΔΨ) of Streptococcus mutans and Lactobacillus casei
No full textPolyvinyl chloride membrane electrodes sensitive to tetraphenyl phosphonium (TPP+), butyltriphenyl phosphonium (bTPP+), and methyltriphenyl phosphonium (mTPP+) ions have been compared for the determination of the electrical potential difference (ΔΨ) of the oral bacteria, Streptococcus mutans DR0001 6 and Lactobacillus casei RB1014. All three types of electrode proved suitable for determining Δ,gY, although the TPP+-sensitive electrode was particularly susceptible to interference by protonmotive force (Δp) dissipators known to inhibit sugar uptake by the bacteria. The mTPP+-sensitive electrode was the least affected. Similarly, both strains had high nonspecific binding capacity for TPP+ and bTPP+ ions, and this increased for all three ions when the bacteria were heated to 80°C for 1 h to abolish glucose uptake and metabolism. This heat-treatment procedure is therefore not a suitable control for determination of nonspecific binding to cells. However, 1% ( v v) toluene, 20 μm gramicidin, or 10 μm valinomycin effectively depolarized the bacteria without interfering with nonspecific binding. The ionophores were therefore used subsequently for the determination of nonspecific binding of the lipid-soluble cations. The mTPP+ ion and corresponding electrode proved the most effective system, and ΔΨ values of -89 and -107 mV were obtained for S. mutans and L. casei, respectively, harvested from glucose-limited continuous cultures and incubated in 100 mm Hepes-KOH buffer (pH 7.0), containing 1 mm dithiothreitol and 10 mm glucose. Although the ΔΨ of S. mutans decreased significantly in the presence of Mes-KOH and potassium phosphate buffers at pH 7.0, it increased to -119 mV in Tris-HCl buffer (pH 7.0). Addition of 100 mm KCl to the Tris buffer showed that the inhibiting effects of the former buffers resulted from their high K+ content. Glucose uptake and acid production by both strains was also markedly inhibited by high concentrations of Na+. The measuring system revealed that the ΔΨ of both strains decreased by up to 50% in the presence of 100 mm Na+, supporting the proposed role for Na+ in the deenergization of Δp in oral bacteria.</p
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