Five of fifty five strains of Salmonella typhimurium of human origin was hybridized with both the LT-A and LT-B gene of Escherichia coli. The remarkably erythromatous and indurated response on rabbit skin and significant elongation of Chinese Hamster Ovary (CHO) cells indicated the production of enterotoxin of these isolates. The Salmonella enterotoxin is heat-labile and is not a secretory product. The LT gene of E. coli was used to analyze the chromosome and plasmid DNA from Salmonella typhimurium strains for toxin gene sequences. Southern blot analysis demonstrated that the toxin gene was located on the plasmid but not on the chromosome. Restriction enzymes BamHI, EcoRI, HindIII and PstI were used to analyze the DNA isolated from salmonella strains Nos.22, 52, 55 and 59. Three DNA fragments with size of 5.2 Kb of strain 22, 5.0 Kb of strain 52 and 8.6 Kb of strain 59 were identified as containing the enterotoxin gene. Plasmid pUC19 was used as the vector to clone these DNA fragments in E. coli. The rabbit skin permeability test indicated that Salmonella enterotoxin could be synthesized at readily detectable levels in these transformed E. coli.
Abstract Leptospirosis, caused by pathogenic Leptospira spp., has recently been recognized as an emerging infectious disease worldwide. Despite its severity and global importance, knowledge about the molecular pathogenesis and virulence evolution of Leptospira spp. remains limited. Here we sequenced and analyzed 102 isolates representing global sources. A high genomic variability were observed among different Leptospira species, which was attributed to massive gene gain and loss events allowing for adaptation to specific niche conditions and changing host environments. Horizontal gene transfer and gene duplication allowed the stepwise acquisition of virulence factors in pathogenic Leptospira evolved from a recent common ancestor. More importantly, the abundant expansion of specific virulence-related protein families, such as metalloproteases-associated paralogs, were exclusively identified in pathogenic species, reflecting the importance of these protein families in the pathogenesis of leptospirosi s . Our observations also indicated that positive selection played a crucial role on this bacteria adaptation to hosts. These novel findings may lead to greater understanding of the global diversity and virulence evolution of Leptospira spp.
Edwardsiella tarda is a Gram-negative, facultative aerobic pathogen which infects multifarious hosts including fish, amphibians and human beings. A twin-arginine translocation (Tat) gene cluster important for high-salt tolerance in E. tarda was identified previously. Here the genetic structure and pleiotropic roles of the Tat system in physiological adaptation of the bacterium were further characterized. Functional analysis indicated that tatD was not required for Tat export process and tatE might be an allelic gene of tatA in the bacterium. The results showed that disruption in the Tat system did not affect the morphology and biofilm formation in E. tarda, but did affect motility, hemagglutination, cell aggregation and infection of eukaryotic cells (e.g. macrophage J774a). Comparative proteomics analysis of subcellular proteins using two-dimensional gel electrophoresis and a qualitative shotgun protein sequencing method were implemented to identify proteins differentially expressed in E. tarda EIB202 vs. ∆tatABCD. The results revealed a large repertoire of differentially expressed proteins (n = 61), shedding light on the Tat system associated with virulence and stress-associated processes in E. tarda.
Neuroblastoma (NB) is one of the most lethal childhood cancers due to its propensity to become treatment resistant. By spatial mapping of subclone geographies before and after chemotherapy across 89 tumor regions from 12 NBs, we find that densely packed territories of closely related subclones present at diagnosis are replaced under effective treatment by islands of distantly related survivor subclones, originating from a different most recent ancestor compared to lineages dominating before treatment. Conversely, in tumors that progressed under treatment, ancestors of subclones dominating later in disease are present already at diagnosis. Chemotherapy treated xenografts and cell culture models replicate these two contrasting scenarios and show branching evolution to be a constant feature of proliferating NB cells. Phylogenies based on whole genome sequencing of 505 individual NB cells indicate that a rich repertoire of parallel subclones emerges already with the first oncogenic mutations and lays the foundation for clonal replacement under treatment.
Edwardsiella tarda is the etiologic agent of edwardsiellosis, a devastating fish disease prevailing in worldwide aquaculture industries. Here we describe the complete genome of E. tarda, EIB202, a highly virulent and multi-drug resistant isolate in China.E. tarda EIB202 possesses a single chromosome of 3,760,463 base pairs containing 3,486 predicted protein coding sequences, 8 ribosomal rRNA operons, and 95 tRNA genes, and a 43,703 bp conjugative plasmid harboring multi-drug resistant determinants and encoding type IV A secretion system components. We identified a full spectrum of genetic properties related to its genome plasticity such as repeated sequences, insertion sequences, phage-like proteins, integrases, recombinases and genomic islands. In addition, analysis also indicated that a substantial proportion of the E. tarda genome might be devoted to the growth and survival under diverse conditions including intracellular niches, with a large number of aerobic or anaerobic respiration-associated proteins, signal transduction proteins as well as proteins involved in various stress adaptations. A pool of genes for secretion systems, pili formation, nonfimbrial adhesions, invasions and hemagglutinins, chondroitinases, hemolysins, iron scavenging systems as well as the incomplete flagellar biogenesis might feature its surface structures and pathogenesis in a fish body.Genomic analysis of the bacterium offered insights into the phylogeny, metabolism, drug-resistance, stress adaptation, and virulence characteristics of this versatile pathogen, which constitutes an important first step in understanding the pathogenesis of E. tarda to facilitate construction of a practical effective vaccine used for combating fish edwardsiellosis.
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