17,519 research outputs found
AgandCuloadedonTiO2/graphite as a catalyst for �Escherichia coli- contaminated water disinfection
No full textTiO2 film was synthesized by means of the chemical bath deposition (CBD) method from TiCl4
as a precursor and surfactant cetyl trimethyl ammonium bromide (CTAB) as a linking and assem-
bling agent of the titanium hydroxide network on a graphite substrate. Ag and Cu were loaded
on the TiO2 film by means of electrodeposition at various applied currents. Photoelectrochemical
testing on the composite of Ag–TiO2/G and Cu–TiO2/G was used to define the composite for
Escherichia coli-contaminated water disinfection. Disinfection efficiency and the rate of disinfection
of E. coli-contaminated water with Ag–TiO2/G as a catalyst was higher than that observed for
Cu–TiO2/G in all disinfection methods including photocatalysis (PC), electrocatalysis (EC), and
photoelectrocatalysis (PEC). The highest rate constant was achieved by the PEC method using
Ag–TiO2/G, k was 6.49 × 10−2
CFU mL−1
min−1
. Effective disinfection times of 24 h (EDT24)
and 48 h (EDT48) were achieved in all methods except the EC method using Cu–TiO2/G.
Keywords: Ag–TiO2/G, Cu–TiO2/G, Escherichia coli, disinfectio
Preferential attachment of Escherichia coli to different particle size fractions of an agricultural grassland soil.
No full textThis study reports on the attachment preference of a faecally derived bacterium, Escherichia coli, to soil particles of defined size fractions. In a batch sorption experiment using a clay loam soil it was found that 35% of introduced E. coli cells were associated with soil particulates >2 μm diameter. Of this 35%, most of the E. coli (14%) were found to be associated with the size fraction 15-4 μm. This was attributed to the larger number of particles within this size range and its consequently greater surface area available for attachment. When results were normalised with respect to estimates of the surface area available for bacterial cell attachment to each size fraction, it was found that E. coli preferentially attached to those soil particles within the size range 30-16 μm. For soil particles > 2 μm, E. coli showed at least 3.9 times more preference to associate with the 30-16 μm than any other fraction. We report that E. coli can associate with different soil particle size fractions in varying proportions and that this is likely to impact on the hydrological transfer of cells through soil and have clear implications for our wider understanding of the attachment dynamics of faecally derived bacteria in soils of different compositions
Transcriptional Response of Selenopolypeptide Genes and Selenocysteine Biosynthesis Machinery Genes in Escherichia coli during Selenite Reduction
No full textThis work was supported by a United States Department of Agriculture-Cooperative State Research, Education, and Extension Service grant (no. 2009-35318-05032), a Biotechnology Research grant (no. 2007-BRG-1223) from the North Carolina Biotechnology Center, and a startup fund from the Golden LEAF Foundation to the Biomanufacturing Research Institute and Technology Enterprise (BRITE).Bacteria can reduce toxic selenite into less toxic, elemental selenium (Se0), but the mechanism on how bacterial cells reduce selenite at molecular level is still not clear. We used Escherichia coli strain K12, a common bacterial strain, as a model to study its growth response to sodium selenite (Na2SeO3) treatment and then used quantitative real-time PCR (qRT-PCR) to quantify transcript levels of three E. coli selenopolypeptide genes and a set of machinery genes for selenocysteine (SeCys) biosynthesis and incorporation into polypeptides, whose involvements in the selenite reduction are largely unknown. We determined that 5 mM Na2SeO3 treatment inhibited growth by ∼50% while 0.001 to 0.01 mM treatments stimulated cell growth by ∼30%. Under 50% inhibitory or 30% stimulatory Na2SeO3 concentration, selenopolypeptide genes (fdnG, fdoG, and fdhF) whose products require SeCys but not SeCys biosynthesis machinery genes were found to be induced ≥2-fold. In addition, one sulfur (S) metabolic gene iscS and two previously reported selenite-responsive genes sodA and gutS were also induced ≥2-fold under 50% inhibitory concentration. Our findings provide insight about the detoxification of selenite in E. coli via induction of these genes involved in the selenite reduction process.Peer reviewe
Absence in Bacillus subtilis and Staphylococcus aureus of the sequence-specific deoxyribonucleic acid methylation that is conferred in Escherichia coli K-12 by the dam and dcm enzymes
No full textDreiseikelmann B, Wackernagel W. Absence in Bacillus subtilis and Staphylococcus aureus of the sequence-specific deoxyribonucleic acid methylation that is conferred in Escherichia coli K-12 by the dam and dcm enzymes. Journal of Bacteriology. 1981;147(1):259-261.Restriction analysis of plasmid pHV14 deoxyribonucleic acid isolated from Escherichia coli K-12, Bacillus subtilis, and Staphylococcus aureus with restriction endonucleases MboI, Sau3AI, and EcoRII was used to study the methylation of those nucleotide sequences which in E. coli contain the major portions of N6-methyladenine and 5-methylcytosine. The results showed that neither B. subtilis nor S. aureus methylates deoxyribonucleic acid at the same sites and nucleotides which are recognized and methylated by dam and dcm enzymes in E. coli K-12
The lytB gene of Escherichia coli is essential and specifies a product needed for isoprenoid biosynthesis
No full textLytB and GcpE, because they are codistributed with other pathway enzymes, have been predicted to catalyze unknown steps in the nonmevalonate pathway for isoprenoid biosynthesis. We constructed a conditional Escherichia coli lytB mutant and found that LytB is essential for survival and that depletion of LytB results in cell lysis, which is consistent with a role for this protein in isoprenoid biosynthesis. Alcohols which can be converted to pathway intermediates beyond the hypothesized LytB step(s) support limited growth of E. coli lytB mutants. An informatic analysis of protein structure suggested that GcpE is a globular protein of the TIM barrel class and that LytB is also a globular protein. Possible biochemical roles for LytB and GcpE are suggested
Escherichia coli σ70 senses sequence and conformation of the promoter spacer region
No full textIn bacteria, promoter identification by RNA polymerase
is mediated by a dissociable p factor. The
housekeeping σ70 factor of Escherichia coli recognizes
two well characterized DNA sequence
elements, known as the ‘-10’ and ‘-35’ hexamers.
These elements are separated by ‘spacer’ DNA, the
sequence of which is generally considered unimportant.
Here, we use a combination of bioinformatics,
genetics and biochemistry to show that σ70
can sense the sequence and conformation of the
promoter spacer region. Our data illustrate how
alterations in spacer region sequence can increase
promoter activity. This stimulatory effect requires
σ70 side chain R451, which is located in close proximity
to the non-template strand at promoter
position -18. Conversely, R451 is not required to
mediate transcriptional stimulation by improvement
of the -10 element. Mutation of σ70 residue
R451, which is highly conserved, results in reduced
growth rate, consistent with a central role in
promoter recognition
Phenotypic microarrays suggest Escherichia coli ST131 is not a metabolically distinct lineage of extra-intestinal pathogenic E. coli
No full textExtraintestinal pathogenic E. coli (ExPEC) are the major aetiological agent of urinary tract infections (UTIs) in humans. The emergence of the CTX-M producing clone E. coli ST131 represents a major challenge to public health worldwide. A recent study on the metabolic potential of E. coli isolates demonstrated an association between the E. coli ST131 clone and enhanced utilisation of a panel of metabolic substrates. The studies presented here investigated the metabolic potential of ST131 and other major ExPEC ST isolates using 120 API test reagents and found that ST131 isolates demonstrated a lower metabolic activity for 5 of 120 biochemical tests in comparison to non-ST131 ExPEC isolates. Furthermore, comparative phenotypic microarray analysis showed a lack of specific metabolic profile for ST131 isolates countering the suggestion that these bacteria are metabolically fitter and therefore more successful human pathogens
Generation of gene deletions and gene replacements in Escherichia coli O157:H7 using a temperature sensitive allelic exchange system
No full textIn this work we describe protocols for the generation of gene deletions and gene replacements using a temperature sensitive plasmid in Escherichia coli O157:H7. This technology requires flanking DNA to be cloned into a temperature sensitive vector but the resulting clone allows great flexibility for further modification of the target sequence. It is therefore highly suited to the study of genes in which several rounds of changes are envisaged. A number of examples are used to illustrate the flexibility of the system which has been used to create novel gene replacements including fusions for protein localisation work and reporters for transcriptional analyses. In this paper we describe protocols which can be used with a high degree of success when applied to E. coli O157. The deletion and replacement of the LEE4 operon of E. coli O157 is detailed to show the advantages and limitations of the technology
Effect of long-term starvation on the survival, recovery, and carbon utilization profiles of a bovine Escherichia coli O157:H7 isolate from New Zealand
No full textThe ability to maintain a dual lifestyle of colonizing the ruminant gut and surviving in nonhost environments once shed is key to the success of Escherichia coli O157:H7 as a zoonotic pathogen. Both physical and biological conditions encountered by the bacteria are likely to change during the transition between host and nonhost environments. In this study, carbon starvation at suboptimal temperatures in nonhost environments was simulated by starving a New Zealand bovine E. coli O157:H7 isolate in phosphate-buffered saline at 4 and 15°C for 84 days. Recovery of starved cells on media with different nutrient availabilities was monitored under aerobic and anaerobic conditions. We found that the New Zealand bovine E. coli O157:H7 isolate was able to maintain membrane integrity and viability over 84 days and that the level of recovery depended on the nutrient level of the recovery medium as well as the starvation temperature. In addition, a significant difference in carbon utilization was observed between starved and nonstarved cells
Fluoroquinolone-resistant Escherichia coli, Indonesia
No full textIn a recent, population-based survey of 3,996 persons
in Indonesia, fluoroquinolone (FQ)-resistant Escherichia coli
was prevalent in the fecal flora of 6% of patients at hospital
admission and 23% of patients at discharge, but not among
healthy relatives or patients visiting primary healthcare centers
(2%). Molecular typing showed extensive genetic diversity
with only limited clonality among isolates. This finding
suggests that independent selection of resistant mutants
occurs frequently. FQ-resistant isolates exhibited a higher
rate of spontaneous mutation, but sparser virulence profiles,
than FQ-susceptible isolates from the same population. The
resistant isolates belonged predominantly to phylogenetic
groups A (57%) and B1 (22%) but also to the moderately virulent
group D (20%). Hypervirulent strains from the B2 cluster
were underrepresented (1%). Because FQ-resistant E.
coli can cause disease, especially nosocomial infections in
immunocompromised patients, spread of such strains must
be stopped
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