Incompatibility of the Cad plasmid from Yersinia pestis with plasmids of the IncFI group

The relation of Yersinia pestis calcium dependence plasmid (pCad) to known Inc FI (F'lac, R386, pOX38) and IncFV (F0lac) plasmids has been studied. Evidence that plasmid pCad of Yersinia pestis belongs to FI incompatibility group is presented.     

Cloning of the locus encoding synthesis of an outer membrane protein (Omp2) of the calcium dependence plasmid of Yersinia pestis (Lehmann, Neumann)

The genetic locus of Yersinia pestis encoding synthesis of a 46-kDa heat-inducible outer membrane protein (Omp2) was cloned into pBR322 plasmid. The Omp2 was shown to be analogous to previously described YopH and Yop2b proteins. The fifth HindIII fragment of 48-MDa calcium dependence plasmid pCad358 mediates production of 31- and 28-kDa proteins, irrespective of orientation of the insertion. A 31-kDa polypeptide seems to correspond to the YopJ described elsewhere. The maps of BamHI and HindIII of pCad358 region studied differed from those described for pCD1 plasmid of Y. pestis KIM. The products encoded by genes from the fragment cloned in the Pgm+ background give rise to considerable growth of Y. pestis within mouse peritoneal macrophages but were not sufficient to cause lethal infectious process.     

Genetic markers of epidemic strains of Vibrio cholerae

In this review new data on the key pathogenicity genes of V. cholerae are presented. As shown on the basis of the analysis of the latest information on the structure of the genomes of different V. cholerae strains, structural genes ctxAB coding cholera toxin may not serve as the only marker of epidemically dangerous strains. More complete and reliable information for the evaluation of the epidemic potential of V. cholerae isolated from the environment may be obtained by the simultaneous detection of 4 genetic markers: genes ctxAB, tcpA and hap coding, respectively, cholera toxin, toxin-corregulated adhesion pili and soluble hemagglutinin/protease, as well as regulatory virulence gene toxR.     

Molecular-epidemiological characteristic and possible origin of Vibrio cholerae non O1/non O139 with complete and limited set of virulence genes

Study of molecular-epidemiological characteristics of Vibrio cholerae non O1/non O139 serogroup with complete and limited set of virulence genes was performed. Differences of their genes composition as compared to these of O1 serogroup (classic and El Tor biovars) were revealed, which points to their origin from avirulent environmental cholera vibrios.     

Prophage CTXphi genome variability and its role in alteration of Vibrio cholerae El Tor virulence characteristics

Comparative analysis of CTXphi prophage genome of 366 V. cholerae El Tor strains isolated from infected people and water was carried out using the polymerase chain reaction. Four groups of vibrios, which carry different combinations of ctxA, zot, and ace genes from core region of CTXphi prophage coding key (cholera enterotoxin) and accessory (Zot and Ace toxins) pathogenicity factors, were determined: ctxA(+) zot(-) ace(+), ctxA(-) zot(+) ace(+), ctxA(-) zot(+) ace(-), ctxA(-) zot(-) ace(+). Vibrios that had lost all tested genes were also revealed. Genomic rearrangements occurring in water environment in virulent V. cholerae strains, which acquired foreign pathogenicity genes necessary for their existence in human organism, were proposed as one of the mechanisms of formation of clones with an incomplete or no prophage. Infection process in model animals challenged with wild and isogenic strains of V. cholerae differing in the set of the phage genes (ctxA, zot, and ace) was comparatively analyzed. It was shown that variability of CTXphi prophage genome was an important factor of modification of cholera vibrios virulent characteristics. Obtained data point to usefulness of ctxA, zot, and ace phage genes detection in wild V. cholerae isolates as it could permit evaluation of their virulent potential determining the severity of the infection.     

Genetic analysis of biochemical differences of Yersinia pestis strains

Literature data and results of our experimental studies on genetic base of biochemical differentiation of Yersinia pestis strains of various subspecies and biovars are summarized in the review. Data on variability of genes coding biochemical features (sugar and alcohol fermentation, nitrate reduction), the differential development of which are the base of existing phenotypic schemes of Y. pestis strains classification, are presented. Variability of these genes was shown to have possible use for the development of genetic classification of Y. pestis strains of various subspecies and biovars.     

Genome structure and origin of nontoxigenic strains of <Emphasis Type="Italic">Vibrio cholerae</Emphasis> of El Tor biovar with different epidemiological significance

Intraspecies genetic differentiation of nontoxigenic strains of Vibrio cholerae of El Tor biovar containing one of the key pathogenicity genes, tcpA, is studied along with the phylogenetic relationships between these strains and toxigenic isolates. Comparative analysis of the whole genome nucleotide sequences demonstrates for the first time that ctxA^–tcpA⁺ strains vary considerably and can be clustered into two separate groups, the CTX_φ–RS1_φ⁺VPI⁺VSP⁺/CTX_φ–RS1_φ–VPI⁺VSP⁺ isolates and the CTX_φ–RS1_φ–VPI⁺VSP^– isolates, differing in their epidemiological significance. In the course of model experiments, it is established that nontoxigenic potentially epidemic CTX_φ–RS1_φ⁺VPI⁺VSP⁺/CTX_φ–RS1_φ–VPI⁺VSP⁺ isolates are derivatives of toxigenic strains. The results of whole genome SNP analysis of 35 Vibrio cholerae strains confirm these data and indicate genetic remoteness of nontoxigenic CTX_φ–RS1_φ–VPI⁺VSP^– strains both from the potentially epidemic strains and from the toxigenic isolates. It is found that the genomes of the CTX_φ–RS1_φ–VPI⁺VSP^– strains contain unique SNPs which are characteristic of them alone. The new data on the structure of the genome of nontoxigenic strains with different epidemiological significance may be further used for their genetic differentiation.     

Prediction of the three-dimensional structure of aflatoxin of Aspergillus flavus by homology modelling

Aflatoxins are polyketide-derived secondary metabolites produced by Aspergillus spp. The toxic effects of aflatoxins have adverse consequences for human health and agricultural economics. The aflR gene, a regulatory gene for aflatoxin biosynthesis, encodes a protein containing a zinc-finger DNA-binding motif. AFLR-Protein three-dimensional model was generated using Robetta server. The modeled AFLR-Protein was further optimization and validation using Rampage. In the simulations, we monitored the backbone atoms and the C-α-helix of the modeled protein. The low RMSD and the simulation time indicate that, as expected, the 3D structural model of AFLR-protein represents a stable folding conformation. This study paves the way for generating computer molecular models for proteins whose crystal structures are not available and which would aid in detailed molecular mechanism of inhibition of aflatoxin.     

A comparative analysis of molecular-genetic peculiarities of the genomes of cholera, plague and anthrax agents and their evolutional transformations

Cholera, plague, and anthrax, the diseases that have accounted for millions of human victims, still endanger the entire mankind by possible development of epidemic outbreaks due to their spread or application as bioterrorist agents. Generalized results of research into the genomic features of the Vibrio cholerae, Yersinia pestis, and Bacillus anthracis are discussed. Despite different frequencies of evolutional transformations occurring in their genomes, that are likely to be associated with diverse life cycles of the pathogens, clones with altered diagnostic, and virulence characteristics were shown to have a fair probability of formation. Also presented in the review, are literature data concerning the main evolutional stages for any of these pathogens, determination of new genetic variants, consideration of the mechanisms facilitating maintenance of the microbial agents during the interepidemic periods.