Multiple copies of hemolysin genes and associated sequences in the chromosomes of uropathogenic Escherichia coli strains.

The O6 serogroup Escherichia coli strain 536 carries two hemolysin (hly) determinants integrated into the chromosome. The two hly determinants are not completely identical, either functionally or structurally, as demonstrated by spontaneous deletion mutants carrying only one of them and by cloning each of the two determinants separately into cosmid vectors. Each hly determinant is independently deleted at a frequency of 10(-4), leading to variants which exhibit similar levels of internal hemolysin but different amounts of secreted hemolysin. The two hly determinants were also identified in the O4 E. coli strain 519. The three E. coli strains 251, 764, and 768, which belong to the serogroup O18, and the O4 strain 367 harbor a single chromosomal hly determinant, as demonstrated by hybridization with hly-gene-specific probes. However, a hybridization probe derived from a sequence adjacent to the hlyC-proximal end of the plasmid pHly 152-encoded hly determinant hybridizes with several additional chromosomal bands in hemolytic O18 and O6 E. coli strains and even in E. coli K-12. The size of the probe causing the multiple hybridization suggests a 1,500- to 1,800-base pair sequence directly flanking hlyC. Spontaneous hemolysin-negative mutants were isolated from strains 764 and 768, which had lost the entire hly determinant but retained all copies of the hlyC-associated sequence.2+.     

Synthesis, inactivation, and localization of extracellular and intracellular Escherichia coli hemolysins.

Extra- and intracellular Escherichia coli hemolysin expressed by two cloned hly determinants, both under the control of the activator element hlyR, were analyzed. One determinant carried all four hly genes (hlyC, hlyA, hlyB, and hlyD), whereas the other carried only the two genes (hlyC and hlyA) required for synthesis of active hemolysin but not those essential for its secretion. It was shown that the total amounts of HlyA protein and of hemolytic activity are similar in both cases in logarithmically growing cultures. The E. coli strain carrying the complete hly determinant released most hemolysin into the media and accumulated very little HlyA intracellularly. The active extracellular hemolysin (HlyA*) was inactivated in the stationary phase without degradation of the HlyA protein. In contrast, the hemolysin which accumulated intracellularly in the E. coli strain carrying hlyA and hlyC only was proteolytically degraded at the end of the logarithmic growth phase. Immunogold labeling indicates that active intracellular HlyA bound preferentially to the inner membrane, whereas that part of the extracellular HlyA which remained cell-bound was located exclusively at the cell surface. It was shown by fluorescence-activated cell sorter analysis that active extra- and intracellular HlyA* bound with similar efficiency to erythrocytes, whereas hemolytically inactive HlyA protein did not bind to these target cells.     

Relationship between plasmid and chromosomal hemolysin determinants of Escherichia coli

Plasmid hemolysin (hly) determinants have been shown previously to comprise three cistrons (hlyA, hlyB, hlyC), coding for the synthesis and transport of hemolysin. Using recombinant plasmids as specific probes for these cistrons, we were able to analyze the chromosomal hly determinants of nine Escherichia coli strains which belonged to serotypes O4, O6, O18, and O75 and were isolated from urinary tract infections and fecal flora. The chromosomal hly genes shared extensive sequence homology with the cloned plasmid hly determinant. Nevertheless, small differences were observed, and these were found to lie mainly within cistron A (hlyA), which has been shown to determine the hemolysin protein itself. These fine variations were not specific for the O-serotype.     

Nucleotide sequence of a plasmid-encoded hemolysin determinant and its comparison with a corresponding chromosomal hemolysin sequence

Abstract The complete sequence of the plasmid pHly152-encoded hemolysin ( hly ) determinant of Escherichia coli is presented and compared with a recently sequenced chromosomal hly determinant [1]. High sequence homology between the two hly determinants is observed withìn all four structural genes, hlyC, A, B and D , but little sequence similarities are found in the 3'- and 5'-noncoding flanking regions. In addition, the noncoding region upstream of hlyC which carries the promoter for hlyC, A and B , was sequenced for several chromosomal hly determinants. The comparison of these sequences indicates three distinct classes of promoter regions which share common putative −10 and −35 boxes at roughly the same location relative to the start of hlyC .     

The secreted hemolysins of Proteus mirabilis, Proteus vulgaris, and Morganella morganii are genetically related to each other and to the alpha-hemolysin of Escherichia coli.

Secreted hemolysins were extremely common among clinical isolates of Proteus mirabilis, Proteus vulgaris, and Morganella morganii, and hemolytic activity was either cell associated or cell free. Southern hybridization of total DNA from hemolytic isolates to cloned regions of the Escherichia coli alpha-hemolysin (hly) determinant showed clear but incomplete homology between genes encoding production of hemolysins in the four species. One of the two E. coli secretion genes, hlyD, hybridized only with DNA from P. vulgaris and M. morganii, which produced cell-free hemolysis, but not with that from P. mirabilis, which showed only cell-associated activity. Molecular cloning of the genetic determinants of cell-free hemolytic activity from P. vulgaris and M. morganii chromosomal DNA allowed their functional analysis via inactivation with the transposons Tn1000 and Tn5. Both hemolysin determinants were about 7.5 kilobase pairs and comprised contiguous regions directing regulation, synthesis, and specific secretion out of the cell. Transposon mutations which eliminated secretion of the Proteus and Morganella hemolysins could be complemented specifically by the E. coli hemolysin secretion genes hlyB or hlyD. Alignment of the physically and functionally defined hly determinants from P. vulgaris and M. morganii with that of the E. coli alpha-hemolysin confirmed a close genetic relationship but also indicated extensive evolutionary divergence.     

Both alpha-haemolysin determinants contribute to full virulence of uropathogenic Escherichia coli strain 536

Uropathogenic Escherichia coli strain 536 possesses two intact copies of the alpha-haemolysin determinant localised on distinct pathogenicity islands. The coding regions of the two hlyCABD operons are conserved; however, upstream sequences are entirely dissimilar. Consequently, expression of the encoded toxin molecules in vitro is highly different. On the other hand, the contribution of the individual determinants to the strain's virulence is the same. Isogenic mutants lacking individual hly determinants have a similar increase in LD50 value in a mouse model of urinary tract infection. Mouse lung toxicity as well as in vitro assays reveals a significant decrease in acute cytotoxicity of both mutants in comparison to the parent wild-type strain; however, the two hly mutants do not significantly differ from each other in these respects. Single channel recordings show no difference in electrophysiological characteristics of the pores formed by the individual HlyA molecules on synthetic planar lipid membranes. Nor do the paralogues have any target cell preference in an in vitro cytotoxicity assay. Our data suggest that the two hly paralogues encode identical toxin functions; however, due to different regulation of expression, they participate at distinct stages of the infectious process. Interestingly, the unrelated uropathogenic E. coli strain J96 shares the same two hly alleles, suggesting that acquisition of the two paralogues accorded a selective evolutionary advantage.     

Enhanced secretory production of hemolysin-mediated cyclodextrin glucanotransferase in Escherichia coli by random mutagenesis of the ABC transporter system

The hemolysin transport system was found to mediate the release of cyclodextrin glucanotransferase (CGTase) into the extracellular medium when it was fused to the C-terminal 61 amino acids of HlyA (HlyAs(61)). To produce an improved-secretion variant, the hly components (hlyAs, hlyB and hlyD) were engineered by directed evolution using error-prone PCR. Hly mutants were screened on solid LB-starch plate for halo zone larger than the parent strain. Through screening of about 1 × 10(4) Escherichia coli BL21(DE3) transformants, we succeeded in isolating five mutants that showed a 35-217% increase in the secretion level of CGTase-HlyAs(61) relative to the wild-type strain. The mutation sites of each mutant were located at HlyB, primarily along the transmembrane domain, implying that the corresponding region was important for the improved secretion of the target protein. In this study we describe the finding of novel site(s) of HlyB responsible for enhancing secretion of CGTase in E. coli.     

Secretion of the Bordetella pertussis adenylate cyclase from Escherichia coli containing the hemolysin operon

The extracellular calmodulin-sensitive adenylate cyclase produced by Bordetella pertussis is synthesized as a 215-kDa precursor. This polypeptide is transported to the outer membrane of the bacteria where it is proteolytically processed to a 45-kDa catalytic subunit which is released into the culture supernatant [Masure, H.R., & Storm, D.R. (1989) biochemistry 28, 438-442]. The gene encoding this enzyme, cyaA, is part of the cya operon that also includes the genes cyaB, cyaD, and cyaE. A comparison of the predicted amino acid sequences encoded by cyaA, cyaB, and cyaD with the amino acid sequences encoded by hlyA, hlyB, and hlyD genes from the hemolysin (hly) operon from Escherichia coli shows a large degree of sequence similarity [Glaser, P., Sakamoto, H., Bellalou, J., Ullmann, A., & Danchin, A. (1988) EMBO J. 7, 3997-4004]. Complementation studies have shown that HlyB and HlyD are responsible for the secretion of HlyA (hemolysin) from E. coli. The signal sequence responsible for secretion of hemolysin has been shown to reside in its C-terminal 27 amino acids. Similarly, CyaB, CyaD, and CyaE are required for the secretion of CyaA from Bordetella pertussis. We placed the cyaA gene and a truncated cyaA gene that lacks the nucleotides that code for a putative C-terminal secretory signal sequence under the control of the lac promoter in the plasmid pUC-19. These plasmids were transformed into strains of E. coli which contained the hly operon. The truncated cyaA gene product, lacking the putative signal sequence, was not secreted but accumulated inside the cell.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of the α-haemolysin determinant from the human enteropathogenic Escherichia coli O26 plasmid pEO5

The 157-kb conjugative plasmid pEO5 encoding α-haemolysin in strains of human enteropathogenic Escherichia coli (EPEC) O26 was investigated for its relationship with EHEC-haemolysin-encoding plasmids of enterohaemorrhagic E. coli (EHEC) O26 and O157 strains. Plasmid pEO5 was found to be compatible with EHEC-virulence plasmids and did not hybridize in Southern blots with plasmid pO157 from the EHEC O157:H7 strain EDL933, indicating that both plasmids were unrelated. A 9227-bp stretch of pEO5 DNA encompassing the entire α- hly CABD operon was sequenced and compared for similarity to plasmid and chromosomally inherited α- hly determinants. The α- hly determinant of pEO5 (7252 bp) and its upstream region was most similar to corresponding sequences of the murine E. coli α-hly plasmid pHly152, in particular, the structural α- hly CABD genes (99.2% identity) and the regulatory hly R regions (98.8% identity). pEO5 and α-hly plasmids of EPEC O26 strains from humans and cattle were very similar for the regions encompassing the structural α- hly CABD genes. The major difference found between the hly regions of pHly152 and pEO5 is caused by the insertion of an IS 2 element upstream of the hly C gene in pHly152. The presence of transposon-like structures at both ends of the α- hly sequence indicates that this pEO5 virulence factor was probably acquired by horizontal gene transfer.     

Molecular cloning of the F8 fimbrial antigen from Escherichia coli

Abstract The genetic determinant coding for the P-specific F8 fimbriae was cloned from the chromosome of the Escherichia coli wild-type strain 2980 (O18:K5:H5:F1C, F8). The F8 determinant was further subcloned into the Pst I site of pBR322 and a restriction map was established. In a Southern hybridization experiment identity between the chromosomally encoded F8 determinant of 2980 and its cloned counterpart was demonstrated. The cloned F8 fimbriae and those of the wild type strain consist of a protein subunit of nearly 20 kDa. F8 fimbriated strains were agglutinated by an F8 polyclonal antiserum, caused mannose-resistant hemagglutination and attached to human uroepithelial cells. The cloned F8 determinant was well expressed in a variety of host strains.     

Cloning and functional characterization of the plasmid-encoded hemolysin determinant of Escherichia coli.

We cloned the DNA containing the Escherichia coli hemolysin determinant on a small, high-copy plasmid. We generated plasmids containing fragments of this DNA and used them either alone or in two-plasmid complementation systems to define the limits of the structural genes. This system also allowed us to partially characterize the function of each of the gene products in the production and transport of hemolysin. Taken with previously published data, the present experiments indicate the following. (i) At least three cistrons, hlyC, hlyA, and hlyB (these were previously designated cisC, etc. [Noegel et al., Mol. Gen. Genet. 175:343-350, 1979]), contain the specific genetic information for the hemolytic phenotype, (ii) hlyA encodes a 107,000-kilodalton protein, which seems to be an inactive precursor of hemolysin. (iii) Normal amounts of hemolysin activity inactive precursor of hemolysin. (iii) Normal amounts of hemolysin activity require only the products of hlyA and hlyC. This activity was found in the periplasm; very little hemolysin activity was found in the cytoplasm, suggesting that the hlyC product is required for transport or activation of the hlyA product or both. (iv) Active hemolysin remains in the periplasm in the absence of hlyB function, hence the hlyB product seems to be necessary for the transport of hemolysin to the exterior of the cell. We further show that overproduction of the hlyA product is lethal, probably causing lysis of the cell.     

Translocation and compartmentalization of Escherichia coli hemolysin (HlyA).

Hemolysin plasmids were constructed with mutations in hlyB, hlyD, or both transport genes. The localization of hemolysin activity and HlyA protein in these mutants was analyzed by biochemical and immunological methods. It was found that mutants defective in hlyB accumulated internal hemolysin, part of which was associated with the inner membrane and was degraded in the late logarithmic growth phase. In an HlyB+ HlyD- mutant, hemolysin was predominantly localized in the membrane compartment. Labeling of these Escherichia coli cells with anti-HlyA antibody indicated that part of HlyA, presumably the C-terminal end but not the pore-forming domains, was already transported to the cellular surface. This finding suggests that HlyB is able to recognize the C-terminal signal of the HlyA protein and to initiate its translocation across the membranes.     

Cloning of chromosomal DNA encoding the F41 adhesin of enterotoxigenic Escherichia coli and genetic homology between adhesins F41 and K88.

The genetic determinant for production of the adhesive antigen F41 was isolated from a porcine enterotoxigenic Escherichia coli strain by cosmid cloning. The cloned DNA included sequences homologous to those of hybridization probes prepared from the K88 adhesive antigen operon. Transposon insertions which inactivated F41 production mapped to the same region of DNA showing homology with the K88 genes, demonstrating the genetic relatedness of F41 and K88. Hybridization of a K88 gene probe to plasmid and total DNA from the porcine E. coli isolate from which the F41 gene was cloned indicated that F41 is chromosomally encoded by this strain. This observation was extended to other F41-producing animal isolates. A large number of animal E. coli isolates were examined with K88, F41, and K99 gene probes and for mannose-resistant hemagglutination of human group O erythrocytes and K88 and F41 antigen production. All K88 and F41 antigen producers possessed genetic homology with the K88 and F41 gene probes. Most, but not all, F41-producing strains possessed homology to the K99 gene probe, reflecting the previously observed association of F41 and K99 antigen production. In the strains examined, homology with the K99 gene probe was plasmid associated, whereas homology with the F41 gene probe was chromosomal. The K88 antigen-producing strains showed no homology with the K99 probe. A number of strains possessed homology with the K88 and F41 gene probes and were mannose-resistant hemagglutination positive, but did not produce K88 or F41 antigens. This suggests that there are adhesins among animal isolates of E. coli which are genetically related to but antigenically distinct from K88 and F41.