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U Dobrindt

Publications and source records attributed to U Dobrindt.

At least 19 recordsLinked to original sources
PubMed2002

Efficient expression of the alpha-haemolysin determinant in the uropathogenic Escherichia coli strain 536 requires the leuX-encoded tRNA(5)(Leu).

The uropathogenic Escherichia coli strain 536 (O6:K15:H31) carries two alpha-haemolysin determinants which are located on different pathogenicity islands (PAI I(536) and PAI II(536)). PAI II(536) is associated with the tRNA gene leuX. The leuX-encoded tRNA(5)(Leu) is required for the efficient expression of the hly determinants in strain 536. HlyA levels were reduced and secretion of the protein was delayed in the leuX-negative mutant strain 536Delta102. The lack of a functional tRNA(5)(Leu) resulted in a decrease in hly transcript levels in comparison to the wild-type strain. Analysis of several genes whose products are involved in the regulation of hly expression revealed that levels of RfaH and Hha, as well as the corresponding rfaH and hha transcripts, were higher in the leuX-negative background, whereas the expression of tolC and hns was not influenced by the leuX genotype. The analysis of hly transcript levels in hha deletion mutants of the E. coli strains 536 and 536Delta102 demonstrated that the increase in hha expression is partially responsible for the reduction in hly transcript levels in the leuX-negative background. These results demonstrate that the tRNA(5)(Leu) affects the expression of the alpha-haemolysin determinant at different levels in a regulatory cascade, and imply that, in addition to Hha, at least one further, as yet unidentified, regulatory factor must be involved in the regulation of hly transcription in the uropathogenic E. coli strain 536.

Bacterial Proteins↗
PubMed2002

Pathogenicity islands of uropathogenic E. coli and the evolution of virulence.

Uropathogenic Escherichia coli (UPEC) are the most important group of microorganisms responsible for urinary tract infection. UPEC differ from non-pathogenic E. coli and from other E. coli pathotypes by the production of specific virulence factors, which enable the bacteria to adhere to uroepithelial cells and to establish urinary tract infections. Besides adherence factors, toxins, 'modulins', capsules, iron uptake systems and other bacterial products contribute to the virulence of the strains. The respective genes are frequently located on large pieces of DNA called 'pathogenicity islands' (PAIs). PAIs form (unstable) regions of the genome of UPECs, which are often associated with tRNA genes. Using various molecular techniques, the functions of PAI encoded gene products have been studied. The usage of DNA arrays give answers to questions on the distribution of PAIs among various enterobacteria and on the expression of the different genes under in vitro and in vivo conditions. In addition, assumptions can be made on the evolution of these important pathogens.

Escherichia coli↗
PubMed2001

A subtractive hybridisation analysis of genomic differences between the uropathogenic E. coli strain 536 and the E. coli K-12 strain MG1655.

Suppression subtractive hybridisation (SSH) was performed to identify genomic differences between the uropathogenic Escherichia coli strain 536 and the non-pathogenic E. coli K-12 strain MG1655. In total, 22 DNA fragments were isolated which were specific for strain 536. Five of these fragments showed homology to known virulence determinants and four fragments matched genes for lipopolysaccharide (LPS) or capsule biosynthesis and a siderophore receptor. Seven fragments did not show any homology to known genes. These fragments may represent parts of putative pathogenicity islands (PAIs). Whereas two fragments were highly specific for uropathogenic E. coli (UPEC), the other fragments could also be detected among the other tested wild-type strains.

Bacterial Proteins↗
PubMed2001

Regulation of tRNA5Leu-encoding gene leuX that is associated with a pathogenicity island in the uropathogenic Escherichia coli strain 536.

Pathogenicity islands (PAls) contain virulence determinants and are often linked to tRNA loci. The leuX gene encoding tRNA5Leu is associated with PAI II536 of the uropathogenic E. coli strain 536 (O6:K15:H31) and is important for the expression of virulence factors in this strain. Transcription of leuX differs from that of the majority of tRNA genes including the major leucyl-tRNA gene leuV. Availability of the tRNAsLeu can be linked with the efficient expression of virulence determinants. Transcription of leuX and letV was studied to gain further insights into the regulation of this tRNA gene and its role during the expression of virulence determinants. leuX but not letV transcripts accumulated in stationary phase. While leuX transcription was unchanged or slightly up-regulated by an increase in growth temperature, osmolarity or ethanol concentration, that of leuV was reduced. The heat shock-specific sigma factor RpoH was shown to affect transcription of leuX but not of leuV. These results demonstrate that transcription of a tRNA gene can be specifically influenced by an alternative sigma factor. Our finding expands our knowledge of the regulation of tRNA gene transcription and represents an additional mode of regulation of gene expression that can also affect bacterial virulence.

Base Sequence↗
PubMed2001

Whole genome plasticity in pathogenic bacteria.

The exploitation of bacterial genome sequences has so far provided a wealth of new general information about the genetic diversity of bacteria, such as that of many pathogens. Comparative genomics uncovered many genome variations in closely related bacteria and revealed basic principles involved in bacterial diversification, improving our knowledge of the evolution of bacterial pathogens. A correlation between metabolic versatility and genome size has become evident. The degenerated life styles of obligate intracellular pathogens correlate with significantly reduced genome sizes, a phenomenon that has been termed "evolution by reduction". These mechanisms can permanently alter bacterial genotypes and result in adaptation to their environment by genome optimization. In this review, we summarize the recent results of genome-wide approaches to studying the genetic diversity of pathogenic bacteria that indicate that the acquisition of DNA and the loss of genetic information are two important mechanisms that contribute to strain-specific differences in genome content.

Bacteria↗
PubMed2001

Identification and characterization of a novel genomic island integrated at selC in locus of enterocyte effacement-negative, Shiga toxin-producing Escherichia coli.

The selC tRNA gene is a common site for the insertion of pathogenicity islands in a variety of bacterial enteric pathogens. We demonstrate here that Escherichia coli that produces Shiga toxin 2d and does not harbor the locus of enterocyte effacement (LEE) contains, instead, a novel genomic island. In one representative strain (E. coli O91:H(-) strain 4797/97), this island is 33,014 bp long and, like LEE in E. coli O157:H7, is integrated 15 bp downstream of selC. This E. coli O91:H(-) island contains genes encoding a novel serine protease, termed EspI; an adherence-associated locus, similar to iha of E. coli O157:H7; an E. coli vitamin B12 receptor (BtuB); an AraC-type regulatory module; and four homologues of E. coli phosphotransferase proteins. The remaining sequence consists largely of complete and incomplete insertion sequences, prophage sequences, and an intact phage integrase gene that is located directly downstream of the chromosomal selC. Recombinant EspI demonstrates serine protease activity using pepsin A and human apolipoprotein A-I as substrates. We also detected Iha-reactive protein in outer membranes of a recombinant clone and 10 LEE-negative, Shiga toxin-producing E. coli (STEC) strains by immunoblot analysis. Using PCR analysis of various STEC, enteropathogenic E. coli, enterotoxigenic E. coli, enteroaggregative E. coli, uropathogenic E. coli, and enteroinvasive E. coli strains, we detected the iha homologue in 59 (62%) of 95 strains tested. In contrast, espI and btuB were present in only two (2%) and none of these strains, respectively. We conclude that the newly described island occurs exclusively in a subgroup of STEC strains that are eae negative and contain the variant stx(2d )gene.

Amino Acid Sequence↗
PubMed2001

Expression of hemin receptor molecule ChuA is influenced by RfaH in uropathogenic Escherichia coli strain 536.

The outer membrane protein ChuA responsible for hemin utilization has been recently identified in several pathogenic Escherichia coli strains. We report that the regulatory protein RfaH influences ChuA expression in the uropathogenic E. coli strain 536. In an rfaH mutant, the chuA transcript as well as the ChuA protein levels were significantly decreased in comparison with those in the wild-type strain. Within the chuA gene, a consensus motif known as the JUMPStart (just upstream of many polysaccharide associated gene starts) sequence was found, which is shared by RfaH-affected operons. Furthermore, the presence of two different subclasses of the chuA determinant and their distribution in E. coli pathogroups are described.

Bacterial Outer Membrane Proteins↗
PubMed2001

S-Fimbria-encoding determinant sfa(I) is located on pathogenicity island III(536) of uropathogenic Escherichia coli strain 536.

The sfa(I) determinant encoding the S-fimbrial adhesin of uropathogenic Escherichia coli strains was found to be located on a pathogenicity island of uropathogenic E. coli strain 536. This pathogenicity island, designated PAI III(536), is located at 5.6 min of the E. coli chromosome and covers a region of at least 37 kb between the tRNA locus thrW and yagU. As far as it has been determined, PAI III(536) also contains genes which code for components of a putative enterochelin siderophore system of E. coli and Salmonella spp. as well as for colicin V immunity. Several intact or nonfunctional mobility genes of bacteriophages and insertion sequence elements such as transposases and integrases are present on PAI III(536). The presence of known PAI III(536) sequences has been investigated in several wild-type E. coli isolates. The results demonstrate that the determinants of the members of the S-family of fimbrial adhesins may be located on a common pathogenicity island which, in E. coli strain 536, replaces a 40-kb DNA region which represents an E. coli K-12-specific genomic island.

Adhesins, Escherichia coli↗
PubMed2000

Evolution of microbial pathogens.

Various genetic mechanisms including point mutations, genetic rearrangements and lateral gene transfer processes contribute to the evolution of microbes. Long-term processes leading to the development of new species or subspecies are termed macroevolution, and short-term developments, which occur during days or weeks, are considered as microevolution. Both processes, macro- and microevolution need horizontal gene transfer, which is particularly important for the development of pathogenic microorganisms. Plasmids, bacteriophages and so-called pathogenicity islands (PAIs) play a crucial role in the evolution of pathogens. During microevolution, genome variability of pathogenic microbes leads to new phenotypes, which play an important role in the acute development of an infectious disease. Infections due to Staphylococcus epidermidis, Candida albicans and Escherichia coli will be described with special emphasis on processes of microevolution. In contrast, the development of PAIs is a process involved in macroevolution. PAIs are especially important in processes leading to new pathotypes or even species. In this review, particular attention will be given to the fact that the evolution of pathogenic microbes can be considered as a specific example for microbial evolution in general.

Candida albicans↗
PubMed2000

Toxin genes on pathogenicity islands: impact for microbial evolution.

Toxin-specific genes are often located on mobile genetic elements such as phages, plasmids and pathogenicity islands (PAIs). The uropathogenic E. coli strain 536 carries two alpha-hemolysin gene clusters, which are part of the pathogenicity islands I536 and II536, respectively. Using different genetic techniques, two additional PAIs were identified in the genome of the E. coli strain 536, and it is likely that further PAIs are located on the genome of this strain. Pathogenicity islands are often associated with tRNA genes. In the case of the E. coli strain 536, the PAI-associated tRNA gene leuX, which encodes a minor leucyl-tRNA, affects the expression of various virulence traits including alpha-hemolysin production. The exact mode of action of the tRNA5Leu-dependent gene expression has to be identified in the future.

Bacterial Toxins↗
PubMed2000

Influence of pathogenicity islands and the minor leuX-encoded tRNA5Leu on the proteome pattern of the uropathogenic Escherichia coli strain 536.

The uropathogenic Escherichia coli strain 536 (O6:K15:H31) carries four distinct DNA regions in its chromosome, termed pathogenicity islands (PAIs I536 to IV536). Each of these PAIs encodes at least one virulence factor. All four PAIs are associated with tRNA genes. PAI I536 and PAI II536 can be spontaneously deleted from the chromosome by homologous recombination between flanking direct repeats. The deletion of PAI II536 results in the truncation of the associated gene leuX encoding the tRNALeu. This tRNA influences the expression of various virulence traits. In order to get a deeper insight into the role of PAI I536/II536 and of the tRNA5LeU for the protein expression, the protein expression patterns of Escherichia coli 536 and different derivatives were studied. Differences in the protein expression patterns of the wild-type strain Escherichia coli 536, its mutants 536-21 (PAI I536-, PAI II536-, leuX-), 536delta102 (PAI I536+, PAI II536+, leuX-) as well as of the strain 536R3 (PAI I536-, PAI II536-, leuX+) were analyzed by two-dimensional polyacrylamide gel electrophoresis and MALDI-TOF mass spectrometry. We identified about 39 different intracellular proteins whose expression is markedly altered in the different strain backgrounds. These differences can be linked either to the presence or absence of the PAI I536 and PAI II536 or to that of the tRNA gene leuX. The identities of 34 proteins have been determined by MALDI-TOF-MS. The identification of five proteins was not possible. The results suggest that proteome analysis is an efficient approach to study differences in global gene expression. The comparison of protein expression patterns of the uropathogenic E. coli strain 536 and different derivatives revealed that in this strain the expression of various proteins including those encoded by many housekeeping genes is affected by the presence of PAI I536 and Pai II536 or by that of the tRNA5Leu.

Bacterial Proteins↗
PubMed1998

The leuX-encoded tRNA5(Leu) but not the pathogenicity islands I and II influence the survival of the uropathogenic Escherichia coli strain 536 in CD-1 mouse bladder mucus in the stationary phase.

The uropathogenic Escherichia coli strain 536 carries two pathogenicity islands, each of which is associated with either of the tRNA genes selC or leuX, respectively. Growth competition in CD-1 mouse mucus between the wild-type strain E. coli 536, its leuX mutant 536 delta 102 and its mutant 536R3, lacking both pathogenicity islands but expressing a functional tRNA5(Leu), revealed a major impact of leuX on E. coli survival in bladder mucus. The impaired survival in CD-1 mouse mucus observed upon deletion of the leuX gene was abolished after complementation with the leuX gene. The survival of bacteria in bladder mucus was not influenced by the presence of pathogenicity islands I and II.

Animals↗
PubMed1997

The Pai-associated leuX specific tRNA5(Leu) affects type 1 fimbriation in pathogenic Escherichia coli by control of FimB recombinase expression.

The uropathogenic Escherichia coli strain 536 (06:K15:H31) carries two large chromosomal pathogenicity islands (Pais). Both Pais are flanked by tRNA genes. Spontaneous deletion of Pai II results in truncation of the leuX tRNA5Leu gene. This tRNA is required for the expression of type 1 fimbriae (Fim) and other virulence factors. Transcription of fimA, encoding the major type 1 fimbrial subunit is controlled by an invertable DNA switch. The inversion is catalysed by two recombinases, FimB and FimE. FimB is able to turn the switch on, FimE only off. The fimB gene of strain 536 contains five TTG codons recognized by tRNA5Leu, fimE contains only two. It was proposed that turning on the fim switch requires efficient translation of FimB, in turn requiring tRNA5Leu. Strains in which the TTG codons in fimB were replaced with CTG codons at the wild-type locus were able to produce type 1 fimbriae in the absence of leuX. fimB transcription was influenced by the presence of leuX, but only slightly affected by the presence or absence of leuX codons in fimB. FimB translation was significantly higher from codon-replaced fimB genes than that of wild-type fimB genes in various strain backgrounds. The fim switch was shown to be switched off in leuX-derivatives of E. coli 536, but could be found in the on position when the codon-altered fimB gene was exchanged into the chromosome of these strains. From these data, it is apparent that tRNA5Leu is required for efficient translation of FimB, in turn, leading to type 1 fimbrial expression.

Bacterial Proteins↗