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At least 703 records · Page 39Linked to original sources
PubMed2005

A new family of mobilizable suicide plasmids based on broad host range R388 plasmid (IncW) and RP4 plasmid (IncPalpha) conjugative machineries and their cognate Escherichia coli host strains.

We describe the construction of the pSW family of conditionally replicating plasmids which are based on the IncX oriV origin (oriV(R6Kgamma)) of replication that is dependent on the pir-encoded protein. We constructed several Escherichia coli derivatives expressing pir from different chromosomal loci, and the pir gene could be transduced by phage P1 to any E. coli strain. These chromosomal constructions generate dapA and thyA knockouts, which lead to diaminopimelate or thymidine auxotrophies, respectively, and they serve to provide absolute counterselection even in rich media. These strains can be easily counterselected if used in plasmid transfer experiments into markerless recipients, and they have been demonstrated to work efficiently in E. coli xVibrio or E. coli xBartonella matings. We constructed different pSW plasmids carrying either the oriT(RP4) or the oriT(R388), and we demonstrated that these derivatives can be efficiently transferred using RP4 and R388 conjugation machineries, respectively. We also constructed two plasmids expressing the R388 conjugation machinery, but lacking the oriT(R388). We demonstrated that these plasmids enabled efficient and exclusive transfer of a pSW-oriT(R388) derivative from E. coli to V. cholerae, and we offer an alternative to the popular RP4-based delivery system.

Conjugation, Genetic↗
PubMed2005

Host range, growth property, and virulence of the smallpox vaccine: vaccinia virus Tian Tan strain.

Vaccinia Tian Tan (VTT) was used as a vaccine against smallpox in China for millions of people before 1980, yet the biological characteristics of the virus remain unclear. We have characterized VTT with respect to its host cell range, growth properties in vitro, and virulence in vivo. We found that 11 of the 12 mammalian cell lines studied are permissive to VTT infection whereas one, CHO-K1, is non-permissive. Using electron microscopy and sequence analysis, we found that the restriction of VTT replication in CHO-K1 is at a step before viral maturation probably due to the loss of the V025 gene. Moreover, VTT is significantly less virulent than vaccinia WR but remains neurovirulent in mice and causes significant body weight loss after intranasal inoculation. Our data demonstrate the need for further attenuation of VTT to serve either as a safer smallpox vaccine or as a live vaccine vector for other pathogens.

Animals↗
PubMed1993

Changes in the host range and growth potential of an HIV-1 clone are conferred by the vpu gene.

vpu, alone among the genes of human immunodeficiency virus type 1 (HIV-1), is unique to this virus, with no analogous reading frame evident in the genomes of either HIV-2 or the related SIVs. Effects of vpu upon levels of virus production from infected cells have been noted, but vpu is dispensable for HIV-1 replication in vitro and its significance in the natural viral life cycle is unclear. We have now identified and characterized a major influence of vpu upon the growth and host cell range of a cloned recombinant HIV-1. This effect required the presence of a second determinant mapping to the 3' end of the env gene, and was not detected in clones incorporating an env gene derived from a different strain of the virus. This indicates that important effects of vpu may have been lost in some experimental systems because of the particular viruses used, and further suggests the involvement of a determinant in the transmembrane glycoprotein of the virus in the action of vpu.

Cell Line↗
PubMed2002

F-like plasmid sequences in enteric bacteria of diverse origin, with implication of horizontal transfer and plasmid host range.

Seventy-eight bacterial isolates from human, animal, and plant hosts, representing eight species of the family Enterobacteriaceae, were screened for F-like plasmid sequences. Of the examined human Escherichia coli strains, 28% harbored one or two of the three F-like, RepFI replication regions, while 35% of the examined animal and all phytopathogenic strains harbored RepFIA-specific sequences. Comparative analysis of Salmonella, Shigella, Erwinia, and E. coli plasmid RepFI sequences showed 100% or very high homology, indicating frequent and recent interspecies gene transfer. The high incidence of RepFIA sequences in enteric bacterial species, including Klebsiella and Erwinia, showed that F-like plasmids are successful in avoiding natural barriers to establishment of horizontally transferred DNA and that in the natural environment conjugal transfer is efficient in diverse ecological niches.

Amino Acid Sequence↗
PubMed2005

The origins of new pandemic viruses: the acquisition of new host ranges by canine parvovirus and influenza A viruses.

Transfer of viruses between hosts to create a new self-sustaining epidemic is rare; however, those new viruses can cause severe outbreaks. Examples of such viruses include three pandemic human influenza A viruses and canine parvovirus in dogs. In each case one virus made the original transfer and spread worldwide, and then further adaptation resulted in the emergence of variants worldwide. For the influenza viruses several changes were required for growth and spread between humans, and the emergence of human H2N2 and H3N2 strains in 1957 and 1968 involved the acquisition of three or two new genomic segments, respectively. Adaptation to humans involved several viral genes including the hemagglutinin, the neuraminidase, and the replication proteins. The canine adaptation of the parvoviruses involved capsid protein changes altering the recognition of the host transferrin receptors, allowing canine transferrin receptor binding and its use as a receptor for cell infection.

Adaptation, Physiological↗
PubMed2003

Microarray analysis of A549 cells infected with rabbitpox virus (RPV): a comparison of wild-type RPV and RPV deleted for the host range gene, SPI-1.

A documented consequence of poxvirus infections is global inhibition of host protein synthesis and reduction in mRNA levels. We examined this mRNA decrease by infecting A549 cells, derived from a human lung carcinoma, with rabbitpox virus (RPV), or RPV deleted for the serine protease inhibitor SPI-1 (RPVDeltaSPI-1), which exhibits a growth defect on A549 cells. At various times postinfection, mRNA profiles were analyzed using Affymetrix U95AV2 microarrays. There was a decline in overall cellular mRNA levels beginning at 2.5 hpi, and by 5 hpi, mRNA levels were drastically reduced for the majority of genes. However, several mRNAs increased, including those of heat-shock genes. Finally, a comparison of host mRNA profiles of RPV- to RPVDeltaSPI-1-infected cells revealed subtle differences in mRNA levels at 5 and 12 hpi. In summary, while there was a global decrease of host mRNA levels, the induction of selected mRNAs may be required for a successful poxvirus infection.

Actins↗
PubMed2004

The cowpox virus host range gene, CP77, affects phosphorylation of eIF2 alpha and vaccinia viral translation in apoptotic HeLa cells.

Host restriction of vaccinia virus has been previously described in CHO and RK13 cells in which a cowpox virus CP77 gene rescues vaccinia virus growth at the viral protein translation level. Here we investigate the restrictive stage of vaccinia virus in HeLa cells using a vaccinia mutant virus (VV-hr) that contains a deletion of 18-kb genome sequences resulting in no growth in HeLa cells. Insertion of CP77 gene into VV-hr generated a recombinant virus (VV-36hr) that multiplied well in HeLa cells. Both viruses could enter cells, initiate viral DNA replication and intermediate gene transcription. However, translation of viral intermediate gene was only detected in cells infected with VV-36hr, indicating that CP77 relieves host restriction at the intermediate gene translation stage in HeLa cells. Caspase-2 and -3 activation was observed in HeLa cells infected with VV-hr coupled with dramatic morphological alterations and cleavage of the translation initiation factor eIF4G. Caspase activation was reduced in HeLa cells infected with VV-36hr, indicating that CP77 acts upstream of caspase activation. Enhanced phosphorylation of PKR and eIF2alpha was also observed in cells infected with VV-hr and was suppressed by CP77. Suppression of eIF4G cleavage with the caspase inhibitor ZVAD did not rescue virus translation, whereas expression of a mutant eIF2alpha protein with an alanine substitution of serine at amino acid position 51 (eIF2alphaS51A) partially restored viral translation and moderately increased virus growth in HeLa cells.

Animals↗
PubMed1986

Region VI of cauliflower mosaic virus encodes a host range determinant.

A domain of cauliflower mosaic virus (CaMV) which controls systemic spread in two solanaceous hosts (Datura stramonium and Nicotiana bigelovii) was mapped to the first half of open reading frame 6. Whereas ordinary strains of CaMV are unable to infect solanaceous species except to replicate locally in inoculated leaves, a new CaMV strain (D4) induces chlorotic local lesions and systemically infects both D. stramonium and N. bigelovii. To determine which portion of the CaMV genome controls systemic spread of the virus in solanaceous hosts, nine recombinant genomes constructed between D4 and two ordinary strains of the virus were tested for their ability to infect solanaceous hosts. A 496-base-pair DNA segment comprising the first half of open reading frame 6 specified the type of local lesions and systemic spread of the virus in solanaceous hosts. Exchange of this segment of the genome between strains of CaMV converted a compatible host reaction to an incompatible (hypersensitive) one in response to infection. This suggests that the gene VI protein interacts with the plant to suppress hypersensitivity, the normal response of solanaceous hosts to CaMV infection.

DNA, Viral↗
PubMed1993

Mosquito host range and specificity of Edhazardia aedis (Microspora: Culicosporidae).

Edhazardia aedis was transmitted horizontally to its natural host, Aedes aegypti, and to 6 alternate hosts: Ae. albopictus, Ae. triseriatus, Ae. taeniorhynchus, Anopheles quadrimaculatus, Orthopodomyia signifera and Toxorhynchites rutilus rutilus. The microsporidium produced both binucleate and uninucleate spores in all susceptible hosts. Transovarial transmission, however, was only successful in Ae. aegypti. Therefore, while E. aedis can infect a variety of mosquito species from diverse genera, it is specific for its natural host, Ae. aegypti. Five other mosquito species were not susceptible to E. aedis.

Aedes↗
PubMed1996

Broad-host-range plasmid replication: an open question.

Many factors can influence the ability of plasmids to colonize different hosts, efficient replication probably being the most critical one. Two major strategies seem to facilitate promiscuous plasmid replication: (i) initiation independent of host initiation factors; and (ii) versatile communication between plasmid and host initiation factors. Appropriate communication between a replicon and the different hosts, which becomes crucial at the initation of plasmid replication, plays a major role in plasmid promiscuity. Fused replicons or mechanisms that rescue collapsed replication forks may increase the efficiency of plasmid propagation. However, their contribution to plasmid promiscuous replication remains to be fully evaluated. Several examples of host-specific adaptation of promiscuous plasmids point to an enormous flexibility of these replicons.

DNA Replication↗
PubMed2003

Influenza type A in humans, mammals and birds: determinants of virus virulence, host-range and interspecies transmission.

The virulence of a virus is determined by its ability to adversely affect the host cell, host organism or population of host organisms. Influenza A viruses have been responsible for four pandemics of severe human respiratory disease this century. Avian species harbour a large reservoir of influenza virus strains, which can contribute genes to potential new pandemic human strains. The fundamental importance of understanding the role of each of these genes in determining virulence in birds and humans was dramatically emphasised by the recent direct transmission of avian influenza A viruses to humans, causing fatal infection but not community spread. An understanding of the factors involved in transmission between avian and mammalian species should assist in the development of better surveillance strategies for early recognition of influenza A virus strains having human pandemic potential, and possibly in the design of anti-viral strategies.

Animals↗
PubMed1979

Plaque formation by a host range mutant of vaccinia virus in non-permissive cells co-infected with Yaba virus.

A host-dependent conditional lethal mutant of vaccinia virus strain DIs was rescued to form plaques in a non-permissive cell line JINET co-infected with Yaba virus, a poxvirus serologically distant from the rescued virus. The efficiency of plaque formation under optimal conditions in this system was comparable to that in Vero cells which were permissive for the mutant. The plaque number of the mutant in JINET cells was influenced greatly by the multiplicity of Yaba virus, the interval between inoculations with DIs and Yaba virus and the maintenance medium for pre-infection of cells with Yaba virus. The plaque formation by DIs in JINET cells was suppressed or inhibited when the duration of pre-infection with high multiplicities of Yaba virus was prolonged. Thus, Yaba virus possessed both rescuing and inhibitory activities on DIs and the plaque number of DIs in doubly infected cells was thought to be determined by the balance between the two activities. Ultraviolet light-inactivated Yaba virus retained rescuing activity on DIs in JINET cells.

Animals↗
PubMed1999

Identification of a putative Salmonella enterica serotype typhimurium host range factor with homology to IpaH and YopM by signature-tagged mutagenesis.

The genetic basis for the host adaptation of Salmonella serotypes is currently unknown. We have explored a new strategy to identify Salmonella enterica serotype Typhimurium (S. typhimurium) genes involved in host adaptation, by comparing the virulence of 260 randomly generated signature-tagged mutants during the oral infection of mice and calves. This screen identified four mutants, which were defective for colonization of only one of the two host species tested. One mutant, which only displayed a colonization defect during the infection of mice, was further characterized. During competitive infection experiments performed with the S. typhimurium wild type, the mutant was defective for colonization of murine Peyer's patches but colonized bovine Peyer's patches at the wild-type level. No difference in virulence between wild type and mutant was observed when calves were infected orally with 10(10) CFU/animal. In contrast, the mutant possessed a sixfold increase in 50% lethal morbidity dose when mice were infected orally. The transposon in this mutant was inserted in a 2.9-kb pathogenicity islet, which is located between uvrB and yphK on the S. typhimurium chromosome. This pathogenicity islet contained a single gene, termed slrP, with homology to ipaH of Shigella flexneri and yopM of Yersinia pestis. These data show that comparative screening of signature-tagged mutants in two animal species can be used for scanning the S. typhimurium genome for genes involved in host adaptation.

Amino Acid Sequence↗
PubMed1992

Signaling and host range variation in nodulation.

Rhizobium, Bradyrhizobium, and Azorhizobium strains, collectively referred to as rhizobia, elicit on their leguminous hosts, in a specific manner, the formation of nodules in which they fix nitrogen. Rhizobial nod genes, which determine host specificity, infection, and nodulation, are involved in the exchange of low molecular weight signal molecules between the plant and the bacteria as follows. Transcription of the nod operons is under the control of NodD regulatory proteins, which are specifically activated by plant flavonoid signals. The common and species-specific structural nod genes are involved in turn in the synthesis of specific lipo-oligosaccharides that signal back to the plant to elicit root-hair deformations, cortical-cell divisions, and nodule-meristem formation.

Fabaceae↗