Impact of Ag2S NPs on soil bacterial community - A terrestrial mesocosm approach

Soils might be a final sink for Ag₂S nanoparticles (NPs). Still, there are limited data on their effects on soil bacterial communities (SBC). To bridge this gap, we investigated the effects of Ag₂S NPs (10 mg kg^-1 soil) on the structure and function of SBC in a terrestrial indoor mesocosm, using a multi-species design. During 28 days of exposure, the SBC function-related parameters were analysed in terms of enzymatic activity, community level physiological profile, culture of functional bacterial groups [phosphorous-solubilizing bacteria (P-SB) and heterotrophic bacteria (HB)], and SBC structure was analysed by 16S rRNA gene-targeted denaturing gradient gel electrophoresis. The SBC exposed to Ag₂S NPs showed a significative decrease of functional parameters, such as β-glucosidase activity and L-arginine consumption, and increase of the acid phosphatase activity. At the structural level, significantly lower richness and diversity were detected, but at later exposure times compared to the AgNO₃ treatment, likely because of a low dissolution rate of Ag₂S NPs. In fact, stronger effects were observed in soils spiked with AgNO₃, in both functional and structural parameters. Changes in SBC structure seem to negatively correlate with parameters related to phosphorous (acid phosphatase activity) and carbon cycling (abundance of HB, P-SB, and β-glucosidase activity). Our results indicate a significant effect of Ag₂S NPs on SBC, specifically on parameters related to carbon and phosphorous cycling, at doses as low as 10 mg kg^-1 soil. These effects were only observed after 28 days, highlighting the importance of long-term exposure experiments for slowly dissolving NPs.

Molecular conservation of marsupial and eutherian placentation and lactation

Eutherians are often mistakenly termed 'placental mammals', but marsupials also have a placenta to mediate early embryonic development. Lactation is necessary for both infant and fetal development in eutherians and marsupials, although marsupials have a far more complex milk repertoire that facilitates morphogenesis of developmentally immature young. In this study, we demonstrate that the anatomically simple tammar placenta expresses a dynamic molecular program that is reminiscent of eutherian placentation, including both fetal and maternal signals. Further, we provide evidence that genes facilitating fetal development and nutrient transport display convergent co-option by placental and mammary gland cell types to optimize offspring success.

Fate assessment of engineered nanoparticles in solids dominated media - Current insights and the way forward

Exposure assessment of engineered nanoparticles (ENPs) in soil and sediment is severely hampered by a lack of understanding of the underlying processes and of the impact of matrix constituents on the fate of ENPs in natural systems, including porewater properties like pH, ionic strength, and presence of naturally occurring (nano)particles. Additional issues such as lack of proper methods for in-situ assessment of ENP speciation, ENP ageing, and agglomeration state, hinder proper exposure assessment. Let alone that the lack does not allow for development of predictive methods for endpoints like transformation and agglomeration potential. This paper discusses current approaches for fate assessment of ENPs in solids dominated media and addresses the most prominent knowledge gaps and how these may be addressed. It is concluded that the key issue to be dealt with, are the attachment and deposition processes that are characteristic for ENPs as opposed to equilibrium-driven partitioning processes of non-particulate organic and inorganic contaminants.

Functional conservation of the lncRNA NEAT1 in the ancestrally diverged marsupial lineage: Evidence for NEAT1 expression and associated paraspeckle assembly during late gestation in the opossum Monodelphis domestica

Long non-coding RNAs (lncRNAs) are widely expressed and play various roles in cell homeostasis. However, because of their low conservation at the sequence level, recapitulating lncRNA evolutionary history is often challenging. While performing an ultrastructural analysis of viral particles present in uterine glands of gestating opossum females, we serendipitously noticed the presence of numerous structures similar to paraspeckles, nuclear bodies which in human and mouse cells are assembled around an architectural NEAT1/MENϵ/β lncRNA. Here, using an opossum kidney (OK) cell line, we confirmed by immuno-electron microscopy the presence of paraspeckles in marsupials. We then identified the orthologous opossum NEAT1 gene which, although poorly conserved at the sequence level, displays NEAT1 characteristic features such as short and long isoforms expressed from a unique promoter and for the latter an RNase P cleavage site at its 3'-end. Combining tissue-specific qRT-PCR, in situ hybridization at the optical and electron microscopic levels, we show that (i) NEAT1 is paraspeckle-associated in opossum (ii) NEAT1 expression is strongly induced in late gestation in uterine/placental extracts (iii) NEAT1 induction occurs in the uterine gland nuclei in which paraspeckles were detected. Finally, treatment of OK cells with proteasome inhibitors induces paraspeckle assembly, as previously observed in human cells. Altogether, these results demonstrate that paraspeckles are tissue-specific, stress-responding nuclear bodies in marsupials, illustrating their structural and functional continuity over 200 My of evolution throughout the mammalian lineage. In contrast, the rapid evolution of the NEAT1 transcripts highlights the relaxed constraint that, despite functional conservation, is exerted on this lncRNA.

Paleovirology of 'syncytins', retroviral env genes exapted for a role in placentation

The development of the emerging field of 'paleovirology' allows biologists to reconstruct the evolutionary history of fossil endogenous retroviral sequences integrated within the genome of living organisms and has led to the retrieval of conserved, ancient retroviral genes 'exapted' by ancestral hosts to fulfil essential physiological roles, syncytin genes being undoubtedly among the most remarkable examples of such a phenomenon. Indeed, syncytins are 'new' genes encoding proteins derived from the envelope protein of endogenous retroviral elements that have been captured and domesticated on multiple occasions and independently in diverse mammalian species, through a process of convergent evolution. Knockout of syncytin genes in mice provided evidence for their absolute requirement for placenta development and embryo survival, via formation by cell-cell fusion of syncytial cell layers at the fetal-maternal interface. These genes of exogenous origin, acquired 'by chance' and yet still 'necessary' to carry out a basic function in placental mammals, may have been pivotal in the emergence of mammalian ancestors with a placenta from egg-laying animals via the capture of a founding retroviral env gene, subsequently replaced in the diverse mammalian lineages by new env-derived syncytin genes, each providing its host with a positive selective advantage.

Differential evolutionary fate of an ancestral primate endogenous retrovirus envelope gene, the EnvV syncytin, captured for a function in placentation

Syncytins are envelope genes of retroviral origin that have been co-opted for a role in placentation. They promote cell–cell fusion and are involved in the formation of a syncytium layer—the syncytiotrophoblast—at the materno-fetal interface. They were captured independently in eutherian mammals, and knockout mice demonstrated that they are absolutely required for placenta formation and embryo survival. Here we provide evidence that these “necessary” genes acquired “by chance” have a definite lifetime with diverse fates depending on the animal lineage, being both gained and lost in the course of evolution. Analysis of a retroviral envelope gene, the envV gene, present in primate genomes and belonging to the endogenous retrovirus type V (ERV-V) provirus, shows that this captured gene, which entered the primate lineage >45 million years ago, behaves as a syncytin in Old World monkeys, but lost its canonical fusogenic activity in other primate lineages, including humans. In the Old World monkeys, we show—by in situ analyses and ex vivo assays—that envV is both specifically expressed at the level of the placental syncytiotrophoblast and fusogenic, and that it further displays signs of purifying selection based on analysis of non-synonymous to synonymous substitution rates. We further show that purifying selection still operates in the primate lineages where the gene is no longer fusogenic, indicating that degeneracy of this ancestral syncytin is a slow, lineage-dependent, and multi-step process, in which the fusogenic activity would be the first canonical property of this retroviral envelope gene to be lost.

Syncytins are “new” genes encoding the envelope protein of captured endogenous retroviral elements. Their unambiguous status of “cellular gene” was recently demonstrated by knocking them out in genetically modified mice, showing their absolute requirement for placenta formation and embryo survival, via formation by cell–cell fusion of the feto-maternal syncytium interface. These genes are remarkable, as they are “necessary” for a basic function in placental mammals and yet they were acquired “by chance” on multiple occasions and independently in diverse mammalian species. We proposed that syncytins have been pivotal for the emergence of animals with a placenta from those laying eggs via the capture of a founding retroviral env gene, then subsequently replaced in the diverse mammalian lineages upon successive and independent germline infections by new retroviruses and co-optation of their env gene, each new gene providing its host with a positive selective advantage. This hypothesis would account for the diversity of the captured syncytins that can be currently found, concomitant with the diversity of placental architectures. A consequence of this paradigm is that evidence for “decaying syncytins” in eutherian mammals should exist, and this is precisely what we sought—and found—in this study.

A syncytin-like endogenous retrovirus envelope gene of the guinea pig specifically expressed in the placenta junctional zone and conserved in Caviomorpha

Syncytins are genes of retroviral origin that have been co-opted by mammalian hosts for a function in placentation. Two such genes have already been identified in simians, as well as two distinct, unrelated ones in Muridae and a fifth in the rabbit. Here we searched for similar genes in the guinea pig, which belongs to the Caviomorpha lineage within the Hystricognathi suborder of rodents and displays a placental structural organization with several characteristic features comparable to those of the human organ, including deep trophoblast invasion of maternal tissues. An in silico search for envelope (env) genes with full coding capacity identified a candidate gene that showed specific expression in the placenta, as revealed by RT-qPCR using RNAs from a large panel of tissues. This gene belongs to an endogenous retroviral element present at a single-copy in the guinea pig genome, still displaying a retroviral organization - with a degenerate gag and pol, but an intact env gene. In situ hybridization of guinea pig placenta sections demonstrated specific expression at the level of the invasive trophoblast-containing junctional zone, as observed in humans for syncytin-1 and consistent with a role in invasion of the maternal uterine tissues. The identified gene displays a conserved open reading frame in the Caviomorpha, consistent with an entry date >30 million years, and sequence analyses showed purifying selection of the gene. Conclusively, despite the absence of a demonstrated fusogenic activity, it is likely that the identified env gene - that we named syncytin-like env-Cav1 - exerts a physiological function possibly related to trophoblast invasion, in the course of caviomorph placentation.

Effects of carbonation and leaching on porosity in cement-bound waste

Porosity is possibly an important parameter with respect to leaching of constituents from cement monoliths. During its lifetime, the pore structure of cementitious matrices changes due to carbonation and leaching. This paper discusses the effects of both accelerated carbonation and continuous leaching on the porosity, and, conversely, how porosity affects leaching properties. Two sample types are investigated: a mortar with MSWI-bottom ash substituting the sand fraction and a cement paste with 30 wt% of the cement substituted by a flue gas cleaning residue. The samples have been intensively carbonated in a 20% CO(2) atmosphere for up to 60 days and were subsequently leached. The porosity was investigated by mercury intrusion porosimetry. Accelerated carbonation decreases total porosity by 12% in the case of 60 days of treatment of bottom ash mortars, whereas continuous leaching during 225 days increases it by 16%. Both carbonation and leaching decrease the amount of smaller capillary pores. Carbonation decreases both porosity and pH. Decreasing porosity diminishes leaching of sodium and potassium, while the decrease in pH increases leaching. However, the former process dominates the latter, resulting in a net decreasing effect of carbonation on the release of sodium and potassium from these cement matrices.

A MAGE-A4 peptide presented by HLA-A2 is recognized by cytolytic T lymphocytes

The MAGE-encoded antigens that are recognized by cytolytic T lymphocytes (CTL) are shared by many tumors and are strictly tumor specific. Clinical trials involving therapeutic vaccination of cancer patients with MAGE antigenic peptides or proteins are in progress. To increase the range of patients eligible for therapy with peptides, it is important to identify additional MAGE epitopes. We have used a method to identify CTL epitopes, which selects naturally processed peptides. CD8(+) T cells, obtained from individuals without cancer, were stimulated with autologous dendritic cells infected with a recombinant adenovirus containing the MAGE-A4 coding sequence. Responder cell microcultures that specifically lysed autologous EBV-transformed B cells infected with vaccinia-MAGE-A4 were cloned using autologous stimulator cells infected with a Yersinia enterocolitica carrying the MAGE-A4 sequence. An anti-MAGE-A4 CTL clone was obtained and the epitope was found to be decapeptide GVYDGREHTV (amino acids 230-239) presented by HLA-A2 molecules. The CTL clone lysed HLA-A2 tumor cells expressing MAGE-A4. This is the first reported antigenic peptide encoded by MAGE-A4. It may be valuable for cancer immunotherapy because MAGE-A4 is expressed in 51% of lung carcinomas and 63% of esophageal carcinomas, whereas about 50% of Caucasians and Asians express HLA-A2.

YopB and YopD constitute a novel class of Yersinia Yop proteins

Virulent Yersinia species harbor a common plasmid that encodes essential virulence determinants (Yersinia outer proteins [Yops]), which are regulated by the extracellular stimuli Ca2+ and temperature. The V-antigen-encoding operon has been shown to be involved in the Ca(2+)-regulated negative pathway. The genetic organization of the V-antigen operon and the sequence of the lcrGVH genes were recently presented. The V-antigen operon was shown to be a polycistronic operon having the gene order lcrGVH-yopBD (T. Bergman, S. Håkansson, A. Forsberg, L. Norlander, A. Macellaro, A. Bäckman, I. Bölin, and H. Wolf-Watz, J. Bacteriol. 173:1607-1616, 1991; S. B. Price, K. Y. Leung, S. S. Barve, and S. C. Straley, J. Bacteriol. 171:5646-5653, 1989). We present here the sequence of the distal part of the V-antigen operons of Yersinia pseudotuberculosis and Yersinia enterocolitica. The sequence information encompasses the yopB and yopD genes and a downstream region in both species. We conclude that the V-antigen operon ends with the yopD gene. This conclusion is strengthened by the observation of an insertion-like element downstream of the yopD gene. The translational start codons of YopB and YopD have been identified by N-terminal amino acid sequencing. By computer analysis, the yopB and yopD gene products were found to be possible transmembrane proteins, and YopD was shown to contain an amphipathic alpha-helix in its carboxy terminus. These findings contrast with the general globular pattern observed for other Yops. Homology between Yersinia LcrH and Shigella flexneri IppI and between Yersinia YopB and S. flexneri IpaB was found, suggesting conservation of this locus between these two genera. YopB was also found to have a moderate level of homology, especially within the hydrophobic regions, to members of the RTX protein family of alpha-hemolysins and leukotoxins, indicating that YopB might exhibit a similar function.

Secretion of Yop proteins by Yersiniae

Upon incubation at 37 degrees C in the absence of Ca2+ ions, pathogenic strains of the genus Yersinia cease growing and produce large amounts of a series of plasmid-encoded proteins involved in pathogenicity. These proteins, called Yops (for Yersinia outer membrane proteins), are detected in both the outer membrane fraction and the culture supernatant. We present here the nucleotide sequence of genes yop20 and yop25 from Yersinia enterocolitica O:9. Protein Yop25 is very similar to YopE, the corresponding protein from Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica O:8 (A. Forsberg and H. Wolf-Watz, J. Bacteriol. 172:1547-1555, 1990). This is the first report of a yop20 sequence of yersiniae. We present evidences that Yops are not membrane proteins. Their detection in the membrane fraction results either from copurification of large aggregates of extracellular Yops with the membrane fraction or from the adsorption of released proteins to the cell surface. In contrast with Yops, protein P1 has characteristics of a true membrane protein. The release of Yops by Y. enterocolitica occurs by a novel secretion mechanism that does not involve the cleavage of a typical signal sequence or the recognition of a carboxy-terminal domain.

Cervical myelopathy: MRI evaluation of cord compression

In order to assess the consequences of cervical spinal cord compression in cervical myelopathy, MRI measurements of the sagittal diameter of the cervical spinal cord were obtained in 50 normal volunteers and 50 patients suffering from cervical myelopathy. Whatever the degree of stenosis, the values obtained in the latter group are significantly inferior to those of the normal control group (average mean diameter: normal group: 8.2 mm; cervical myelopathy: 6.2 mm).

Site-specific recombinations between direct and inverted res sites of Tn2501

The resolvase gene and the putative res site of Tn2501 are not closely related to any of the previously described resolution functions. In view of this divergence, we designed genetic experiments to confirm the localization of the res site. We analyzed the activity of the Tn2501-encoded resolvase on substrates containing either directly or invertedly repeated res sites. These experiments confirm the localization of the res site that was predicted from nucleotide sequence data and show that the Tn2501 resolvase promotes site-specific inversions in vivo.

Identification of additional virulence determinants on the pYV plasmid of Yersinia enterocolitica W227

This paper describes the mutagenesis of the pYV plasmid from Yersinia enterocolitica W22703 (serotype O:9) with Tn2507, a new element generating operon fusions. Analysis of the mutants allowed the identification of an additional Yop protein called Yop20 and the mapping of yop20, yop44, yop48, and lcrV, the gene encoding the V antigen. The last gene appeared to be part of an operon that also may contain yop37 and yop44. At 37 degrees C, mutants affected in this operon grew poorly, irrespective of the presence of Ca2+, or they even died in the presence of Ca2+. This operon is thus involved in the regulation by Ca2+, and we called it car, for Ca2+ regulation. It is presumably the Y. enterocolitica counterpart of the lcrGVH operon of Yersinia pestis. Transcription of yop20 and of the car operon was strongly regulated by temperature and only slightly by calcium. Hence, these genes behaved like the other genes of the yop regulon. Mutants affected in yop20 or in yop48 were markedly less virulent for the desferrioxamine-treated mouse than was the parental strain. Yop20 and Yop48 thus probably are Yersinia virulence factors.

MRI assessment of unsuspected dural sinus thrombosis

In three patients with clinically unsuspected diagnosis, MRI has afforded a positive and conspicuous demonstration of dural sinus thrombosis, allowing specific treatment and followed by improvement in the patients' condition. Even in retrospect, CT examinations were nondiagnostic. Presenting symptoms were usual and nonspecific. CT and radionuclide scanning have proved valuable when performed on a clinically oriented basis. Angiography cannot be carried out without clear indications. MRI offers advantages in being a non-invasive technique without ionising radiation, allowing direct visualization and accurate delineation of the thrombus. MRI is definitely the method of choice to assess clinically suspected cerebral venous occlusion. As MRI diagnosis relies on a routine examination protocol, we believe that it will detect other unsuspected cases of dural sinus thrombosis.

Homology between virF, the transcriptional activator of the Yersinia virulence regulon, and AraC, the Escherichia coli arabinose operon regulator

Virulent yersiniae (Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica) restrict their growth at 37 degrees C in rich medium deprived of calcium. This property, called calcium dependency, correlates with the secretion of Yersinia outer membrane proteins (Yops) and with pathogenicity. It is mediated by a 70-kilobase plasmid called pYV. The structural genes of the Yops (yop genes), as well as genes involved in the control of their expression (vir genes), have been localized on pYV. In this communication we show that virF encodes a transcriptional activator controlling the yop regulon. This activator is a 30,879-dalton protein related to AraC, the regulator of the Escherichia coli and Salmonella typhimurium arabinose operons. We also show in this paper that transcription of virF is thermodependent and presumably autoregulated. virF is thus responsible for the effect of temperature on the production of the Yops. Finally, we show that virF activates transcription of the yop genes independently of the presence of calcium ions. The role of calcium therefore remains unaccounted for.

Nucleotide sequence and transcription analysis of yop51 from Yersinia enterocolitica W22703

Virulent strains of Yersinia enterocolitica, pseudotuberculosis and pestis secrete large amounts of plasmid-encoded proteins involved in virulence and called Yops. A 2 kb fragment of the pYVe227 plasmid from Yersinia enterocolitica 0:9 encoding Yop51 was sequenced. Gene yop51 was found to encode a 50,882 Da protein consisting of 468 amino acids. This protein shows 99% identity with Yop2b, its counterpart from Y. pseudotuberculosis YPIII (pIB1), confirming that the virulence machinery is highly conserved among Yersinia spp. The homology stops abruptly 240 bp upstream and 175 bp downstream of the structural yop51 gene suggesting that all the sequences involved in the regulation of yop51 are located within the conserved region and confirming that the homology between the plasmids of Yersinia enterocolitica and Yersinia pseudotuberculosis is made up of boxes of high homology. Gene yop51 is only transcribed at 37 degrees C from a VirF-regulated promoter. This promoter was tentatively identified by determining the messenger transcriptional startpoint. The putative yop51 promoter resembles E. coli promoters despite the fact that it is not active in that species in the absence of VirF. A transcription terminator was found at the end of the gene while a second terminator was detected within the structural gene leading to premature termination of some of the messenger molecules.

Yersinia enterocolitica O:9 as a potential live oral carrier for protective antigens

Yersinia enterocolitica has the capacity to invade the intestinal tissue and to resist the primary host resistance. The former is chromosome coded while the second largely depends on the presence of a 70 kb plasmid called pYV. This plasmid directs the conditional synthesis of high amounts of proteins (YOPs) that are secreted and inserted in the outer membrane. In order to evaluate Y. enterocolitica W22703 as a potential live carrier for immunization, three strains expressing beta-galactosidase (GZ), were tested for their ability to induce an antibody response to this antigen in mice. The first strain contained plasmid pGC1256, a mutated pYV plasmid containing lacZ transcribed from a yop gene promoter. This strain produced high amounts of GZ instead of a YOP protein and was shown to be hypovirulent. The other strains tested were W22703 pYV+ and pYV- containing a derepressed lac operon carried on an independent plasmid. Immunoblot analysis of sera of mice having received by oral inoculation, W22703(pGC1256) or the pYV+ GZ producing strain revealed the presence of antibodies to GZ. The response to GZ after inoculation of W22703(pGC1256) was shown by ELISA to be only slightly inferior to that obtained by subcutaneous injection of GZ. No response was obtained after oral inoculation of the pYV-GZ producing strain. This showed that the presence of pYV was necessary to obtain an antibody response in this system.

A new method for the physical and genetic mapping of large plasmids: application to the localisation of the virulence determinants on the 90 kb plasmid of Salmonella typhimurium

A new method based on transposon-promoted deletions was used to generate a set of deletions in the 90 kb virulence plasmid of Salmonella typhimurium. The analysis of 16 deletion mutants allowed: (1) construction of the restriction map of the plasmid for HindIII, BamHI and BglII; (2) localisation of the plasmid region involved in virulence; (3) identification of two functional replicons on the plasmid.

Transcription of the yop regulon from Y. enterocolitica requires trans acting pYV and chromosomal genes

Virulent Y. enterocolitica strains restrict their growth at 37 degrees C, in rich medium deprived of calcium. This property, called calcium dependency, correlates with pathogenicity. It is conditioned by a 70 kb plasmid called pYV. The analysis of calcium independent (Cl) insertion mutants defined a 20 kb region called the calcium region. This region contains at least three transcription units called virA, B and C. In growth restriction conditions, Y. enterocolitica releases and inserts in its outer-membrane several pYV encoded proteins (POMPs). By transposition mutagenesis using a mini-Mu dlac element, we localized plasmid genes encoding POMPs of 84, 51, 30 and 25 kDa. These genes appear to be scattered on pYV, outside the calcium region and to constitute a regulon. Transcription of these yop genes increased by factors of 3.5 (yop84) to 200 (yop51) when temperature was shifted from 25 to 37 degrees C. On the contrary, calcium had only a moderate effect. Transcription was also dependent on the culture medium and on a trans-acting factor encoded by the calcium region. One Cl double mutant severely affected in transcription of yop51 defined a new locus called virF in the calcium region of pYV. Transcription of the yop genes was very poor in E. coli K12, even in the presence of a fully functional calcium region.

Tn2501, a component of the lactose transposon Tn951, is an example of a new category of class II transposable elements

Tn2501 is a cryptic class II transposon found as part of the lactose transposon Tn951. Insertional inactivation and nucleotide sequence analysis of Tn2501 allowed us (i) to localize the transposase (tnpA) and the resolvase (tnpR) genes as well as the resolution site (res) of Tn2501 and (ii) to compare Tn2501 with other well-known elements of the two subgroups of class II transposons (Tn3, gamma delta, Tn951, IS101; and Tn21, Tn501, Tn1721). The genetic organization of Tn2501 is similar to that of Tn3 with divergent transcription of the tnpA and tnpR genes away from the intervening res site. The tnpR gene of Tn2501 shows weak homology with that of Tn3 and even less with those of Tn21 and Tn501. However, the tnpA gene and the inverted repeat sequences of Tn2501 present more homology with those of Tn21 and Tn501 than with those of Tn3. Complementation studies showed that TnpA- mutants of Tn2501 can be complemented, at a low frequency, by the Tn21 transposase. None of the tested transposons complemented TnpR- mutants of Tn2501.

Yersinia enterocolitica, a primary model for bacterial invasiveness

Yersinia enterocolitica is now the species of Yersinia most frequently isolated from human and animal infections. The species includes pathogens and ubiquitous strains. Among the human pathogens, those isolated in America are more virulent than those isolated elsewhere, especially in Europe and Japan, and these isolates differ biochemically and serologically. The relation between Y. enterocolitica and Y. pestis only became obvious in 1980 with the discovery that at 37 degrees C Y. enterocolitica requires Ca++, a phenotype described in the 1960s for Y. pestis. This requirement as well as virulence is dependent on a 70-kilobase plasmid found later in Y. pseudotuberculosis and Y. pestis. Thus, many bacteriologists elected Y. enterocolitica as a model for bacterial invasiveness. However, studies with non-American strains were impeded by the lack of an inexpensive, simple animal test, a difficulty now circumvented by supplying an appropriate siderophore to the bacteria. Ca++ dependence can be viewed as a transition between free growth and protection against the immune system. In the latter phase, Y. enterocolitica synthesizes and releases large amounts of six plasmid-encoded outer membrane proteins. Most of these are under the control of the plasmid region governing Ca++ dependence. Mutants in this region either lose the Ca++ requirement at 37 degrees C or become unable to grow at 37 degrees C irrespective of the Ca++ concentration. The complex events leading to Ca++ dependence is still not understood. Virulence in Y. enterocolitica also depends on chromosomal genes: the endocytosis in intestinal epithelial cells seems not to be encoded by the pYV plasmid. Studies of Y. pseudotuberculosis suggest that this property depends on a single chromosomal locus, the study of which might be particularly important in the understanding of the first step in infection.

Comparison of serogrouping and polyacrylamide gel electrophoresis for typing Clostridium difficile

A typing scheme for Clostridium difficile based on slide agglutination with rabbit antisera was previously described. It allows the differentiation of 10 serogroups designated A, B, C, D, F, G, H, I, K, and X. We studied the correlation between serogrouping and polyacrylamide gel electrophoresis (PAGE) of whole-cell proteins. A total of 202 isolates from different sources were analyzed by PAGE after ultrasonic disintegration of cells from an 18-h liquid culture and treatment with sodium dodecyl sulfate and 2-mercaptoethanol. A total of 21 different patterns were observed. The reference strains from the 10 serogroups showed different profiles. For each serogroup except A, the patterns obtained with the clinical isolates were identical to the patterns obtained with the reference strains. For the 48 strains belonging to serogroup A, 12 different profiles were observed. Five of these involved strains isolated from patients with antibiotic-associated diarrhea. Typing by sodium dodecyl sulfate-PAGE thus correlates with serogrouping. In addition, it allows discrimination within the heterogeneous serogroup A.

Genetic analysis of the plasmid region controlling virulence in Yersinia enterocolitica 0:9 by Mini-Mu insertions and lac gene fusions

Enteropathogenic strains of Yersinia enterocolitica harbor a virulence plasmid (pYVe plasmid) of 70 kilobases (kb) which specifies, at 37 degrees C, a calcium requirement for growth, autoagglutinability, resistance to the bactericidal activity of human serum, and the expression of outer membrane proteins (OMP). Some mutations suppress the calcium requirement for growth while others make the bacteria unable to grow at 37 degrees C, even in the presence of calcium. To analyse the genes involved in these latter phenotypes, the plasmid of a serogroup 0:9 strain was subjected to transposon mutagenesis with a Mini-Mu (Kan, lac) element. The mapping of 15 insertions and the analysis of transcription showed that at least four transcription units, spanning 22 kb, are involved in the phenomenon of calcium dependence. Mutations in two divergent units (virA and virB) suppressed the requirement for calcium at 37 degrees C. When insertions occurred in the other units (virC and virD), the Y. enterocolitica host became thermosensitive for growth. VirA, B and C mutants did no longer express the pYVe dependent OMPs. VirD mutants expressed and released these proteins save two of mol. wt 37,400 and 40,800 daltons. Transcription of the lac genes in the four groups of mutants was dependent on temperature.

Tn951 derivatives designed for high-frequency plasmid-specific transposition and deletion mutagenesis

We describe the construction of a system allowing high-frequency transposition and deletion mutagenesis with class-II transposons containing a kanamycin or a chloramphenicol-resistance marker. The system utilizes the transposition function of Tn3 and the resolution function of Tn951/Tn2501 which leads to an uncoupling of the resolution and repression functions. It consists of defective transposons inserted into conjugative, replication thermosensitive plasmids. The properties of the system are: easily selectable resistance markers, high transposition frequencies onto plasmids, low transposition frequencies onto the host chromosome, placement of the tnpA gene outside the transposons so that "second-generation" transposition does not occur, possibility to transpose the whole system onto other plasmid vectors with different selection strategies, consecutive use of two transposons for deletion mutagenesis and restriction mapping.

A simple adult-mouse test for tissue invasiveness in Yersinia enterocolitica strains of low experimental virulence

The virulence of Yersinia enterocolitica depends on the presence of a 70-kilobase plasmid, called the Vwa plasmid. This situation is particularly favourable for studies of the mechanism of pathogenicity, but these are hindered by the lack of a suitable animal test to monitor the virulence of the human-pathogenic strains isolated outside the USA which belong to serogroups O:3, O:9 and O:5,27. We observed that, after oral administration to the mouse, the Vwa-positive strains of these serogroups produce a discrete systemic infection while the Vwa-negative strains do not. We present here a simple mouse-virulence test based on this observation.

A restriction map of virulence plasmid pVYE439-80 from a serogroup 9 Yersinia enterocolitica strain

A restriction map of the virulence plasmid pVYE439-80, isolated from Yersinia enterocolitica 439-80 (serogroup 9) was constructed for EcoRI, BamHI, SstII, and SmaI. The mapping was done after cloning of about two-thirds of the plasmid in Escherichia coli. The restriction pattern was compared to those obtained with plasmids isolated from Y. enterocolitica strains of serogroups 1, 3, and 5b. The restriction sites are particularly conserved in a region of about 25 kb. This region contains fragments that are also conserved in serogroup 8 strains [J. Heeseman, C. Keller, R. Morawa, N. Schmidt, H. J. Siemens, and R. Lauf (1983) J. Infect. Dis. 147, 107-115] and that were shown, in strains from this serogroup, to encode calcium dependency [D. A. Portnoy, H. Wolf-Watz, I. Bolin, A. B. Beeder, and S. Falkow, (1984) Infect. Immun. 43, 108-114].

Detection and characterization of Tn2501, a transposon included within the lactose transposon Tn951

The DNA sequence spanning coordinates 9.9 to 16.4 kilobases of the lactose transposon Tn951 ( Cornelis et al., Mol. Gen. Genet. 160:215-224, 1978) constitutes a transposable element by itself. Unlike Tn951 ( Cornelis et al., Mol. Gen. Genet. 184:241-248, 1981), this element, called Tn2501 , transposes in the absence of any other transposon. Transposition of Tn2501 proceeds through transient cointegration and duplicates 5 base pairs of host DNA. Tn2501 is flanked by nearly perfect inverted repeats (44 of 48), related to the inverted repeats of Tn21 ( Zheng et al., Nucleic Acids Res. 9:6265-6278, 1982). Unlike Tn21 , Tn2501 does not confer mercury resistance.

Study of the incompatibility and replication of the 70-kb virulence plasmid of Yersinia

The 70-kb virulence plasmid, vir, from four Yersinia enterocolitica and one Y. pseudotuberculosis strains are incompatible with IncFI plasmids F'Lac and R386 while they are compatible with plasmids representing nine other incompatibility groups. Hybridization experiments carried out on one of these virulence plasmids showed that it contains the F incompatibility determinant D, incD. This determinant was cloned onto pACYC184 and the recombinant clone expressed incompatibility with F'Lac. We conclude that the incompatibility observed between F or R386 and the 70-kb virulence plasmid of Y. enterocolitica and Y. pseudotuberculosis is mediated by incD. Replication genes (rep) from the same plasmid were cloned independently in Escherichia coli. Rep and incD map on two different BamHI fragments. Surprisingly, the replicon isolated is not sensitive to inc D incompatibility. Apart from incD, vir and F share extremely little homology. In particular, there is no evidence for the presence of an F-like transfer operon on vir.

Haemoglobin measurement: the reliability of some simple techniques for use in a primary health care setting

The reliability of five simple techniques for the estimation of blood haemoglobin levels was studied under laboratory conditions. The methods tested were the Sahli technique, the Tallqvist method, and the Lovibond comparator with undiluted blood, blood diluted in Drabkin solution, and blood diluted in modified Drabkin solution. The Lovibond comparator technique using undiluted blood was satisfactory in terms of precision and accuracy, and seems suitable for the monitoring of individual patients and for screening for anaemia. The other techniques were less reliable.A detailed procedure was worked out for estimation of the number of screening errors that can be expected with each of these techniques in any epidemiological situation.

Transposon Tn951 (TnLac) is defective and related to Tn3

Tn951 is flanked by two perfect inverted repeats of 41 bp which include the 38 bp sequence of the IR of Tn3. Tn951 also contains the last 100 bp of the tnpA gene but with at least two mutations. However, beyond nucleotide 137 the sequences diverge and hybridization experiments show that Tn951 lacks at least the first two thirds of the tnpA gene. In agreement with these observations Tn951 does not transpose by itself at a detectable frequency but can be complemented by the tnpA gene of Tn801 or Tn3. Tn501, Tn1721 and gamma delta do not complement Tn951 transposition. Transposition of Tn951 duplicates 5 bp of target DNA sequence.

Plasmid-encoded lysine decarboxylation in Proteus morganii

As a rule, Proteus morganii does not decarboxylate lysine. However, lysine-positive P. morganii strains have been recently described. We suspected a plasmid origin for this atypical character, and we analyzed 14 strains to study this question. Among these strains, 8 yielded lysine-negative segregants after acridine orange or ethidium bromide treatment, and 10 transferred their lysine-positive character to a recipient P. morganii strain. All of the 14 strains analyzed at least segregated or conjugated. Three lysine-positive transconjugants, in turn, segregated lysine-negative variants after ethidium bromide treatment. The eight wild-type lysine-positive strains that segregated lysine-negative subclones contained a large (35 to 45 megadaltons) plasmid detectable by agarose gel electrophoresis. Similarly, the 10 lysine-positive transconjugants contained a plasmid of the same size, whereas P. morganii 1000, the recipient strain, did not contain any detectable plasmid. The large plasmid clearly disappeared in 9 of 11 lysine-negative segregants analyzed. It is concluded that the lysine-positive character of these P. morganii strains is plasmid encoded, and the taxonomical implications are discussed.

Sequence relationships between plasmids carrying genes for lactose utilization

Southern hybridization experiments carried out between pSC101::Tn951 DNA and lambda dlac DNA allowed the location and orientation of the lac operon within the transposon to be deduced. The same method was used to detect Tn951 on Lac plasmids from 11 independent isolates from three continents. None of these plasmids was found to carry an entire Tn951 sequence but they all contained lac genes homologous to the lac genes of Tn951. The lac operon of one of these plasmids was bordered by a sequence homologous to that found at the left-hand side of Tn951. It is concluded that the lac determinants of the Lac plasmids analysed and of Tn951 have evolved from a common ancestor but that the distribution of these determinants cannot be attributed to a spread of the transposon Tn951.

Expression of the lactose transposon Tn951 in Escherichia coli, Proteus and Pseudomonas

The control of beta-galactosidase specified by the lactose transposon Tn951 (inserted into RP1 to give pGC9114) has been studied in Escherichia coli K12, Proteus mirabilis, Pseudomonas aeruginosa and Pseudomonas putida; in the first two species comparison could be made with Flac. In E. coli K12, the Tn951 and chromosomally encoded enzymes showed marked qualitative differences in regulatio, the former giving a substantially lower maximum induced level and induction ratio. Several parameters were slightly affected by strain background. In P. mirabilis, beta-galactosidase control determined by both Flac (in accord with earlier work) and pGC9114 was markedly different from E. coli in that maximal induced levels were about an order of magnitude lower and the induction ratio was reduced to 3 to 5. In Ps. aeruginosa and Ps. putida, Tn951-specified lac expression was qualitatively similar to that in P. mirabilis. Possible reasons for anomalous expression in Proteus and Pseudomonas are discussed.

Deletions and an inversion induced by a resident IS1 of the lactose transposon Tn951

DNA-DNA filter binding tests, "Southern" blotting experiments and DNA heteroduplex analysis clearly show that Tn951 contains an IS1 element. This IS1-951 sequence is peculiar in that it does not contain the PstI cleavage site which is usually observed on E. coli derived IS1 elements. Nonetheless, IS1-951 induces deletions. This process is temperature dependent. One instance of an IS1-951 induced inversion was observed, the structure of which is compatible with the current models of transposition of IS elements.

The lactose transposon Tn951: characterization of transposition

Transposition of the lactose transposon Tn951 was found to still occur in the absence of its original host plasmid pGC1. Transposition was recA-independent. These results show that Tn951 is indeed a transposon. A computer program was developed to facilitate mapping of transposon integration sites in plasmids from restriction data.

Transposition of Tn951 (Tnlac) and cointegrate formation are thermosensitive processes

The frequency of transposition of Tnlac to pGC200, an IncFII R plasmid, increased during the storage of the host strain. This result is explained by the fact that the transpositional event is temperature-dependent: it occurred readily when the host strain was grown at 30 degrees C but it was nearly undetectable when the host strain was grown and kept at 37 degrees C. Fusions between two different plasmids carrying Tnlac with pGC200 were also thermosensitive, suggesting a relation between cointegrate formation and transposition. Lactose did not influence the frequency of transposition of Tnlac.

Multiple integration sites for the lactose transposon Tn 951 on plasmid RP 1 and establishment of a coordinate system for Tn 951

Various molecules generated by transposition of the lactose transposon Tn 951 from plasmid pGC1 to plasmid RP1 were examined by DNA heteroduplex and restriction endonuclease analysis. Tn 951 was found to transpose to at least eight different sites on RP 1 in both possible orientations. A coordinate system for the lactose transposon Tn 951 is constructed.