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  • 1
    Language: English
    In: PLoS ONE, 01 January 2015, Vol.10(3), p.e0117906
    Description: Iron is essential for Escherichia coli growth and survival in the host and the external environment, but its availability is generally low due to the poor solubility of its ferric form in aqueous environments and the presence of iron-withholding proteins in the host. Most E. coli can increase access to iron by excreting siderophores such as enterobactin, which have a very strong affinity for Fe3+. A smaller proportion of isolates can generate up to 3 additional siderophores linked with pathogenesis; aerobactin, salmochelin, and yersiniabactin. However, non-pathogenic E. coli are also able to synthesise these virulence-associated siderophores. This raises questions about their role in the ecology of E. coli, beyond virulence, and whether specific siderophores might be linked with persistence in the external environment. Under the assumption that selection favours phenotypes that confer a fitness advantage, we compared siderophore production and gene distribution in E. coli isolated either from agricultural plants or the faeces of healthy mammals. This population-level comparison has revealed that under iron limiting growth conditions plant-associated isolates produced lower amounts of siderophores than faecal isolates. Additionally, multiplex PCR showed that environmental isolates were less likely to contain loci associated with aerobactin and yersiniabactin synthesis. Although aerobactin was linked with strong siderophore excretion, a significant difference in production was still observed between plant and faecal isolates when the analysis was restricted to strains only able to synthesise enterobactin. This finding suggests that the regulatory response to iron limitation may be an important trait associated with adaptation to the non-host environment. Our findings are consistent with the hypothesis that the ability to produce multiple siderophores facilitates E. coli gut colonisation and plays an important role in E. coli commensalism.
    Keywords: Sciences (General)
    E-ISSN: 1932-6203
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  • 2
    Language: English
    In: Applied and Environmental Microbiology, 2010, Vol. 76(19), p.6514
    Description: The food-borne pathogen Escherichia coli O157:H7 is commonly exposed to organic acid in processed and preserved foods, allowing adaptation and the development of tolerance to pH levels otherwise lethal. Since little is known about the molecular basis of adaptation of E. coli to organic acids, we studied K-12 MG1655 and O157:H7 Sakai during exposure to acetic, lactic, and hydrochloric acid at pH 5.5. This is the first analysis of the pH-dependent transcriptomic response of stationary-phase E. coli. Thirty-four genes and three intergenic regions were upregulated by both strains during exposure to all acids. This universal acid response included genes involved in oxidative, envelope, and cold stress resistance and iron and manganese uptake, as well as 10 genes of unknown function. Acidulant- and strain-specific responses were also revealed. The acidulant-specific response reflects differences in the modes of microbial inactivation, even between weak organic acids. The two strains exhibited similar responses to lactic and hydrochloric acid, while the response to acetic acid was distinct. Acidulant-dependent differences between the strains involved induction of genes involved in the heat shock response, osmoregulation, inorganic ion and nucleotide transport and metabolism, translation, and energy production. E. coli O157:H7-specific acid-inducible genes were identified, suggesting that the enterohemorrhagic E. coli strain possesses additional molecular mechanisms contributing to acid resistance that are absent in K-12. While E. coli K-12 was most resistant to lactic and hydrochloric acid, O157:H7 may have a greater ability to survive in more complex acidic environments, such as those encountered in the host and during food processing.
    Keywords: Gene Expression Profiling ; Gene Expression Regulation, Bacterial ; Stress, Physiological ; Acids -- Toxicity ; Carboxylic Acids -- Toxicity ; Escherichia Coli K12 -- Drug Effects ; Escherichia Coli O157 -- Drug Effects;
    ISSN: 0099-2240
    ISSN: 00992240
    E-ISSN: 10985336
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  • 3
    Language: English
    In: Journal of bacteriology, February 2012, Vol.194(3), pp.686-701
    Description: Lag phase represents the earliest and most poorly understood stage of the bacterial growth cycle. We developed a reproducible experimental system and conducted functional genomic and physiological analyses of a 2-h lag phase in Salmonella enterica serovar Typhimurium. Adaptation began within 4 min of inoculation into fresh LB medium with the transient expression of genes involved in phosphate uptake. The main lag-phase transcriptional program initiated at 20 min with the upregulation of 945 genes encoding processes such as transcription, translation, iron-sulfur protein assembly, nucleotide metabolism, LPS biosynthesis, and aerobic respiration. ChIP-chip revealed that RNA polymerase was not "poised" upstream of the bacterial genes that are rapidly induced at the beginning of lag phase, suggesting a mechanism that involves de novo partitioning of RNA polymerase to transcribe 522 bacterial genes within 4 min of leaving stationary phase. We used inductively coupled plasma mass spectrometry (ICP-MS) to discover that iron, calcium, and manganese are accumulated by S. Typhimurium during lag phase, while levels of cobalt, nickel, and sodium showed distinct growth-phase-specific patterns. The high concentration of iron during lag phase was associated with transient sensitivity to oxidative stress. The study of lag phase promises to identify the physiological and regulatory processes responsible for adaptation to new environments.
    Keywords: Gene Expression Regulation, Bacterial ; Metals -- Metabolism ; Salmonella Typhimurium -- Metabolism
    ISSN: 00219193
    E-ISSN: 1098-5530
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  • 4
    In: Molecular Microbiology, June 2010, Vol.76(5), pp.1250-1265
    Description: The conjugative IncHI1 plasmid pSfR27 from 2a strain 2457T encodes the Sfh protein, a paralogue of the global transcriptional repressor H‐NS. Sfh allows pSfR27 to be transmitted to new bacterial hosts with minimal impact on host fitness, providing a ‘stealth’ function whose molecular mechanism has yet to be determined. The impact of the Sfh protein on the serovar Typhimurium transcriptome was assessed and binding sites for Sfh in the Typhimurium genome were identified by chromatin immunoprecipitation. Sfh did not bind uniquely to any sites. Instead, it bound to a subset of the larger H‐NS regulatory network. Analysis of Sfh binding in the absence of H‐NS revealed a greatly expanded population of Sfh binding sites that included the majority of H‐NS target genes. Furthermore, the presence of plasmid pSfR27 caused a decrease in H‐NS interactions with the Typhimurium chromosome, suggesting that the A + T‐rich DNA of this large plasmid acts to titrate H‐NS, removing it from chromosomal locations. It is proposed that Sfh acts as a molecular backup for H‐NS and that it provides its ‘stealth’ function by replacing H‐NS on the chromosome, thus minimizing disturbances to the H‐NS‐DNA binding pattern in cells that acquire pSfR27.
    Keywords: Fighter Planes -- Analysis ; Chromatin -- Analysis ; Preventive Medicine -- Analysis ; Salmonella Typhimurium -- Analysis ; Genomics -- Analysis;
    ISSN: 0950-382X
    E-ISSN: 1365-2958
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  • 5
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 15 May 2012, Vol.109(20), pp.E1277-86
    Description: More than 50 y of research have provided great insight into the physiology, metabolism, and molecular biology of Salmonella enterica serovar Typhimurium (S. Typhimurium), but important gaps in our knowledge remain. It is clear that a precise choreography of gene expression is required for Salmonella infection, but basic genetic information such as the global locations of transcription start sites (TSSs) has been lacking. We combined three RNA-sequencing techniques and two sequencing platforms to generate a robust picture of transcription in S. Typhimurium. Differential RNA sequencing identified 1,873 TSSs on the chromosome of S. Typhimurium SL1344 and 13% of these TSSs initiated antisense transcripts. Unique findings include the TSSs of the virulence regulators phoP, slyA, and invF. Chromatin immunoprecipitation revealed that RNA polymerase was bound to 70% of the TSSs, and two-thirds of these TSSs were associated with σ(70) (including phoP, slyA, and invF) from which we identified the -10 and -35 motifs of σ(70)-dependent S. Typhimurium gene promoters. Overall, we corrected the location of important genes and discovered 18 times more promoters than identified previously. S. Typhimurium expresses 140 small regulatory RNAs (sRNAs) at early stationary phase, including 60 newly identified sRNAs. Almost half of the experimentally verified sRNAs were found to be unique to the Salmonella genus, and 〈20% were found throughout the Enterobacteriaceae. This description of the transcriptional map of SL1344 advances our understanding of S. Typhimurium, arguably the most important bacterial infection model.
    Keywords: Gene Expression Regulation, Bacterial -- Genetics ; RNA, Small Untranslated -- Genetics ; Regulatory Sequences, Ribonucleic Acid -- Genetics ; Salmonella Typhimurium -- Genetics ; Transcription, Genetic -- Genetics
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 6
    Language: English
    In: BMC Bioinformatics, Feb 3, 2010, Vol.11, p.73
    Description: Background The development of DNA microarrays has facilitated the generation of hundreds of thousands of transcriptomic datasets. The use of a common reference microarray design allows existing transcriptomic data to be readily compared and re-analysed in the light of new data, and the combination of this design with large datasets is ideal for 'systems'-level analyses. One issue is that these datasets are typically collected over many years and may be heterogeneous in nature, containing different microarray file formats and gene array layouts, dye-swaps, and showing varying scales of log.sub.2 - ratios of expression between microarrays. Excellent software exists for the normalisation and analysis of microarray data but many data have yet to be analysed as existing methods struggle with heterogeneous datasets; options include normalising microarrays on an individual or experimental group basis. Our solution was to develop the Batch Anti-Banana Algorithm in R (BABAR) algorithm and software package which uses cyclic loess to normalise across the complete dataset. We have already used BABAR to analyse the function of Salmonella genes involved in the process of infection of mammalian cells. Results The only input required by BABAR is unprocessed GenePix or BlueFuse microarray data files. BABAR provides a combination of 'within' and 'between' microarray normalisation steps and diagnostic boxplots. When applied to a real heterogeneous dataset, BABAR normalised the dataset to produce a comparable scaling between the microarrays, with the microarray data in excellent agreement with RT-PCR analysis. When applied to a real non-heterogeneous dataset and a simulated dataset, BABAR's performance in identifying differentially expressed genes showed some benefits over standard techniques. Conclusions BABAR is an easy-to-use software tool, simplifying the simultaneous normalisation of heterogeneous two-colour common reference design cDNA microarray-based transcriptomic datasets. We show BABAR transforms real and simulated datasets to allow for the correct interpretation of these data, and is the ideal tool to facilitate the identification of differentially expressed genes or network inference analysis from transcriptomic datasets.
    Keywords: Dna Microarrays -- Information Management ; Dna Microarrays -- Research ; Genetic Algorithms -- Usage ; Genetic Algorithms -- Research ; Salmonella -- Genetic Aspects ; Salmonella -- Research ; Salmonellosis -- Genetic Aspects ; Salmonellosis -- Development And Progression ; Salmonellosis -- Research
    ISSN: 1471-2105
    Source: Cengage Learning, Inc.
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  • 7
    Language: English
    In: BMC Bioinformatics, Feb 3, 2010, Vol.11, p.73
    Description: Background The development of DNA microarrays has facilitated the generation of hundreds of thousands of transcriptomic datasets. The use of a common reference microarray design allows existing transcriptomic data to be readily compared and re-analysed in the light of new data, and the combination of this design with large datasets is ideal for 'systems'-level analyses. One issue is that these datasets are typically collected over many years and may be heterogeneous in nature, containing different microarray file formats and gene array layouts, dye-swaps, and showing varying scales of log.sub.2 - ratios of expression between microarrays. Excellent software exists for the normalisation and analysis of microarray data but many data have yet to be analysed as existing methods struggle with heterogeneous datasets; options include normalising microarrays on an individual or experimental group basis. Our solution was to develop the Batch Anti-Banana Algorithm in R (BABAR) algorithm and software package which uses cyclic loess to normalise across the complete dataset. We have already used BABAR to analyse the function of Salmonella genes involved in the process of infection of mammalian cells. Results The only input required by BABAR is unprocessed GenePix or BlueFuse microarray data files. BABAR provides a combination of 'within' and 'between' microarray normalisation steps and diagnostic boxplots. When applied to a real heterogeneous dataset, BABAR normalised the dataset to produce a comparable scaling between the microarrays, with the microarray data in excellent agreement with RT-PCR analysis. When applied to a real non-heterogeneous dataset and a simulated dataset, BABAR's performance in identifying differentially expressed genes showed some benefits over standard techniques. Conclusions BABAR is an easy-to-use software tool, simplifying the simultaneous normalisation of heterogeneous two-colour common reference design cDNA microarray-based transcriptomic datasets. We show BABAR transforms real and simulated datasets to allow for the correct interpretation of these data, and is the ideal tool to facilitate the identification of differentially expressed genes or network inference analysis from transcriptomic datasets.
    Keywords: Dna Microarrays -- Information Management ; Dna Microarrays -- Research ; Genetic Algorithms -- Usage ; Genetic Algorithms -- Research ; Salmonella -- Genetic Aspects ; Salmonella -- Research ; Salmonellosis -- Genetic Aspects ; Salmonellosis -- Development And Progression ; Salmonellosis -- Research
    ISSN: 1471-2105
    Source: Cengage Learning, Inc.
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  • 8
    Language: English
    In: BMC Bioinformatics, 01 February 2010, Vol.11(1), p.73
    Description: Abstract Background The development of DNA microarrays has facilitated the generation of hundreds of thousands of transcriptomic datasets. The use of a common reference microarray design allows existing transcriptomic data to be readily compared and re-analysed in the light of new data, and the combination of this design with large datasets is ideal for 'systems'-level analyses. One issue is that these datasets are typically collected over many years and may be heterogeneous in nature, containing different microarray file formats and gene array layouts, dye-swaps, and showing varying scales of log2- ratios of expression between microarrays. Excellent software exists for the normalisation and analysis of microarray data but many data have yet to be analysed as existing methods struggle with heterogeneous datasets; options include normalising microarrays on an individual or experimental group basis. Our solution was to develop the Batch Anti-Banana Algorithm in R (BABAR) algorithm and software package which uses cyclic loess to normalise across the complete dataset. We have already used BABAR to analyse the function of Salmonella genes involved in the process of infection of mammalian cells. Results The only input required by BABAR is unprocessed GenePix or BlueFuse microarray data files. BABAR provides a combination of 'within' and 'between' microarray normalisation steps and diagnostic boxplots. When applied to a real heterogeneous dataset, BABAR normalised the dataset to produce a comparable scaling between the microarrays, with the microarray data in excellent agreement with RT-PCR analysis. When applied to a real non-heterogeneous dataset and a simulated dataset, BABAR's performance in identifying differentially expressed genes showed some benefits over standard techniques. Conclusions BABAR is an easy-to-use software tool, simplifying the simultaneous normalisation of heterogeneous two-colour common reference design cDNA microarray-based transcriptomic datasets. We show BABAR transforms real and simulated datasets to allow for the correct interpretation of these data, and is the ideal tool to facilitate the identification of differentially expressed genes or network inference analysis from transcriptomic datasets.
    Keywords: Biology
    ISSN: 1471-2105
    E-ISSN: 1471-2105
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  • 9
    In: FEMS Microbiology Letters, 2011, Vol. 325(1), pp.64-70
    Description: Citrobacter rodentium is a mouse pathogen that, because of its similarities with human enteropathogenic (EPEC) and enterohemorrhagic (EHEC) strains of Escherichia coli is widely used as a model system for in vivo and in vitro studies. Similarly to EPEC and EHEC, C. rodentium carries the LEE (locus of enterocyte effacement) pathogenicity island, encoding virulence factors essential for causing transmissible colonic hyperplasia in mice by attaching and effacing (A/E) lesions. Expression of the genes carried by the LEE pathogenicity island is controlled by complex networks of transcriptional factors, including the global regulators H-NS, IHF, and Fis. In this study, we analyzed the role of Lrp, another global regulator of gene expression in enteric bacteria, on the expression of LEE genes of C. rodentium . To this aim, a real-time PCR approach was used and revealed a negative role of Lrp on the expression of all analyzed LEE genes. Mobility-shift experiments indicated that Lrp action is direct on LEE1 and indirect on all other analyzed LEE genes.
    Keywords: Lrp ; Transcriptional Control ; Lee ; Pathogenicity Island ; Virulence ; Enteropathy
    ISSN: 0378-1097
    E-ISSN: 1574-6968
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  • 10
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 25 June 2002, Vol.99(13), pp.8784-9
    Description: For many pathogens, the ability to regulate their replication in host cells is a key element in establishing persistency. Here, we identified a single point mutation in the gene for polynucleotide phosphorylase (PNPase) as a factor affecting bacterial invasion and intracellular replication, and which determines the alternation between acute or persistent infection in a mouse model for Salmonella enterica infection. In parallel, with microarray analysis, PNPase was found to affect the mRNA levels of a subset of virulence genes, in particular those contained in Salmonella pathogenicity islands 1 and 2. The results demonstrate a connection between PNPase and Salmonella virulence and show that alterations in PNPase activity could represent a strategy for the establishment of persistency.
    Keywords: Fimbriae Proteins ; Polyribonucleotide Nucleotidyltransferase -- Metabolism ; Salmonella Enterica -- Pathogenicity
    ISSN: 0027-8424
    E-ISSN: 10916490
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