Methods to study power density distribution in the IVG.1M research reactor after conversion.

In the Republic of Kazakhstan, within the framework of international initiatives on the non-proliferation of nuclear weapons, the IVG.1M research reactor is being converted to low enriched fuel. Due to the change in the fuel composition, it becomes necessary to assess the power density distribution in the fuel assemblies and in the core altogether. Close attention to this parameter is explained by the fact that the non-uniformity of the radial and axial power density fields determines the operating parameters of the reactor, its power, the core resource and the efficiency of fuel utilization. The purpose of this work is approbation of the activation gamma-spectrometry method for determining the power density distribution in the fuel of the IVG.1M research reactor after conversion. Additionally, for a preliminary assessment of the experimental outcomes, the paper presents the MCNP6 calculation results for the power distribution in fuel assemblies and the peaking factors.

[The virulence factors of Mycobacterium tuberculosis: genetic control, new conceptions].

The problem of Mycobacterium tuberculosis virulence, together with drug resistance, is becoming key for the design of drugs with a new mechanism of action and the production of modern concepts and tuberculosis treatment schemes. The review describes gene complexes and their products, including mycolic acids and global regulatory systems at the level of transcriptional, translational, and post-translational modification, etc. The criteria for selection of virulence/pathogenicity factors that might be used for comparative genomic analysis of strains differing in the degree of virulence were recommended. The experimental approaches and test systems for an adequate estimation of the virulence degree of different strains of M. tuberculosis were analyzed.

[Systems of genes and proteins affecting mycobacteria virulence and their homologs participation in conjugation of mycobacterium smegmatis].

This review describes and summarizes the data of ESX secretory system peculiarities characteristic of mainly mycobacteria. This system is involved in the secretion of small proteins of the WXG100 family. Some of these proteins represent virulence factors of Mycobacterium tuberculosis and other pathogenic mycobacteria. The role of these proteins in pathogenesis apparently consists of protecting mycobacteria from lysis in the macrophages that absorb them; the cytolysis of macrophages; and, hence, mycobacterium output into the surrounding tissue. A number of proteins that make up this secretory system are homologs of proteins involved in the conjugation process in saprophytic Mycobacterium smegmatis.

[Mycobacterium tuberculosis mutants with multidrug resistance: history of origin, genetic and molecular mechanisms of resistance, and emerging challenges].

The review summarizes the data on the Mycobacterium tuberculosis mutations that lead to multidrug resistance (MDR) to various antibiotics. MDR strains arose over the past 30 years as a variety of antituberculosis drugs were introduced in medicine, and they largely discount the results of chemotherapy for tuberculosis. The most dangerous of them are strains with extensive drug resistance (XDR), which are resistant to four or five different drugs on average. The molecular mechanisms that make a strain resistant are considered. XDR and MDR strains result from successive and usually independent resistance mutations, which arise in various regions of the mycobacterial genome. In addition, the formation of resistant strains is affected by the phenomenon of tolerance and mycobacterial latency in infected tissues.

[Characterization of the transfer-related tra region of the conjugative plasmid p19 from a Bacillus subtilis soil strain].

The nucleotide sequences of three DNA fragments (total size 30574 bp) of the plasmid p19 from the Bacillus subtilis 19 soil strain have been determined. Thirty open reading frames (ORFs) have been identified in these fragments. oriT of the plasmid has also been identified. As shown by the search for homologs of hypothetical protein products of these ORFs in databases, such homology exists for 18 ORFs. The protein products of nine ORFs can be assumed to have specific functions. Several ORFs were inactivated via insertional mutagenesis, and the conjugation capacity of the mutant plasmids was estimated. According to the data on homology of protein products and the results of ORF inactivation, regions of a total size of about 20 kb from the DNA fragments sequenced by us were inferred to belong to the tra region of p19. As follows from the analysis of the identified ORFs of the p19 tra region, it differs from the earlier described tra regions of other plasmids, irrespective of a certain similarity with the corresponding regions of plasmids of gram-positive bacteria from the genera Bacillus, Clostridium, and Listeria.

[Characteristics of conjugative transfer of Bacillus subtilis chromosomal genes].

Some properties concerning conjugal transmission of chromosomal genes for resistance to antibiotics lincomycin, spectinomycin, and erythromycin that occurs upon contact of cells, which carry a large plasmid p19, and p19 plasmid-free cells are considered in the soil strain Bacillus subtilis 19. Genes were transferred at different rates, depending on the order of their transfer. The transfer of chromosomal genes occurred irrespective of the transmission of self-transmissible autonomous conjugative plasmid p19.

[Additional chromosomes in bacteria: properties and origin].

The review considers papers published over the last 15 years that deal with the presence in cells of some bacterial genera and species of a second chromosome that is smaller than the major one (occasionally, of two additional chromosomes). These additional chromosomes differ from the major one in the set of genes and specific features of replication; however, they carry genes vitally important for the bacterium. The role of these chromosomes and their probable origin from megaplasmids are discussed.

[Molecular analysis of some genes from plasmid p19 of the soil strain Bacillus subtilis 19 involved in conjugation].

Two fragments of conjugative plasmid p19 (95 kb) from the soil strain Bacillus subtilis 19 were cloned and sequenced; these fragments carry genes, products of which are indispensable for the conjugative transfer. One of the fragments 4518 bp in size carries five open reading frames and their fragments (ORF1-ORF5). The protein corresponding to ORF4 is homologous to proteins from the family VirD4. Inactivation of ORF4 and ORF1 by insertional mutagenesis caused a three-to-fivefold decrease in the frequency of plasmid p19 conjugative transfer. Another 2932-bp fragment of p19 was shown to possess a rep region homologous to the rep region of plasmid pBS72 from the soil strain B. subtilis 72 and a novel ORF (ORF6); the protein corresponding to this ORF contains the HTH motif typical for DNA-binding proteins.

[Regularities of the location of genes having different functions and of some other nucleotide sequences in the bacterial chromosome].

The review considers the results of genomic research performed over the last decade that shed light on the location in the bacterial chromosomes of genes having different functions. A tendency towards polarity of the chromosome composition is observed: vitally important genes tend to be concentrated in the region of replication origin (oriC), and their concentration decreases toward the region of replication termination (terC). An oppositely directed polarity (an increase near the terC region) is observed for the distribution of certain oligonucleotides involved in the process of chromosome recombination and segregation.

[Conjugative chromosomal gene transfer in Bacillus subtilis].

Conjugative transfer of 20-kb chromosomal fragment carrying genes encoding tetracycline (tet(r)) and lincomycin (lin(r)) resistance in the soil strain Bacillus subtilis 19 is described. Transfer was preceded by this fragment insertion into the large conjugative pl9cat plasmid producing a hybrid plasmid. Insertion frequency was 10(-4)-10(-5). Then genes tet(r) and lin(r) were transferred to the recipient strains. The transfer of chromosomal genes inserted into the plasmid and plasmid gene cat occurred sequentially and resembled sexduction, which represents chromosomal gene transfer by F'- and R' plasmids during conjugation in Escherichia coli and other gram negative bacteria.

[Comparative characterization of the conjugation capacity and large plasmids in native strains of Bacillus subtilis from different regions of the east European plain].

The properties of large plasmids harbored by Bacillus subtilis strains isolated from soils of Moscow and Moscow oblast and from different regions of the Republic of Belarus have been studied. All large plasmids in the collection of strains from Belarus were capable of conjugative mobilization of the small plasmid pUB110 and were similar in size and other properties. Most of the tested plasmids harbored by strains isolated from Moscow soils had no mobilization ability; they were of different sizes and showed no homology with the replication region of plasmids from the Belarussian collection. The uniformity of the plasmids present in strains from Belarussian soils may be due to their active horizontal transfer under natural conditions.

[A phenomenon of plasmid retrotransfer in conjugation of Bacillus subtilis].

A conjugal retrotransfer-retromobilization of a small nonconjugative plasmid pUB110 was established in Bacillus subtilis. This process involves a large conjugative plasmid p19.

[The bacterial cell cycle: DNA replication, nucleoid segregation, and cell division].

Data on the bacterial cell cycle published in the last 10-15 years are considered, with a special stress on studies of nucleoid segregation between dividing cells. The degree of similarity between the eukaryotic mitotic apparatus and the apparatus performing nucleoid separation is discussed.

[Conjugative transfer of the large plasmid p19 in various Bacillus subtilis strains].

Cryptic conjugative plasmid p19 from the environmental Bacillus subtilis strain 19 was labeled with the cat gene conferring resistance to chloramphenicol. The resulting plasmid, p19cat, was used to estimate the transfer frequency, to study the dynamics of plasmid transfer, and to detect some specific features of conjugation between various B. subtilis strains.

Plasmid transfer in bacilli by a self-transmissible plasmid p19 from a Bacillus subtilis soil strain.

The cryptic 95-kb plasmid p19 of the Bacillus subtilis 19 soil strain promotes the transfer of a small kanamycin resistance plasmid pUB110. To facilitate direct selection for p19 transfer, a plasmid derivative carrying the chloramphenicol resistance gene was constructed. The frequency of transfer of the large plasmid between cells of B. subtilis 19 approached 100% but was more than two orders of magnitude lower when the strain B. subtilis 168 was a recipient. However, when the restriction-deficient strain B. subtilis 168 was a recipient, the transfer efficiency was almost completely recovered. The effectiveness of pUB110 mobilization was virtually not altered in all these cases. pC194 was not mobilized by p19. The kinetics of p19 conjugative transfer is also presented.

[The replication system of plasmids from Bacillus subtilis environmental isolates]. / Kharakteristika sistem replikatsii plazmid prirodnykh shtammov Bacillus subtilis.

Restriction enzyme analysis, cloning, and sequencing showed that large (more than 90-kb) plasmids isolated from different Bacillus subtilis strains are identical in structure of the region ensuring stable inheritance of plasmid replicons and are widespread in Belarussian environmental strains of B. subtilis.