Laboratory of Regulation of Expression of Microorganisms’ Genes

I. Bacterial plasmids: molecular, genetic and functional investigations  (1973—1990).
Genetic control and regulation of the replication of the group of multicopy  colicinogenic  plasmids  have been studied. Plasmids fragments  responsible for its autonomous replication were identified and nucleotide sequence and structure of the replication apparatus  determined.
Mechanisms of the induction of the synthesis of colicins (antibiotics of protein nature encoded plasmid genes) were investigated.  The structure of plasmid ColD colicin operon have been determined.
The mechanism of the protective and enhancing the induced mutagenesis action of colicinogenic  plasmids ColIb and ColIa have been elucidated. It was found that the effect of the plasmids under UV irradiation caused by the action of the plasmid-encoded products - functional analogs of the products of chromosomal genes umuC and umuD
 
II.  Antibiotics of enterobacteria microcins, genetic determinants of synthesis, mechanisms of the action (1990—2006).
The ability of enterobacteria to synthesize antibiotics microcins was studied, the plasmids nature of genes involved in their synthesis has been shown. Microcin C51, nucleotide-peptide antibiotic with unusual structure, found in the Laboratory, and genetic determinants of its synthesis have been investigated. The nucleotide sequence of the microcin operon has been determined and polypeptides related to the synthesis of microcin and immunity to it of producer cells were identified.  The possibility of horizontal transfer of gene cluster associated with the synthesis of microcin C51 has been shown.
The mechanism of inhibition of translation by microcin C has been determined. It was shown that microcin processed inside sensitive cells, forming a modified aspartyl adenylate, a competitive inhibitor of aspartyl-tRNA synthetase (together with K.V. Severinov group).
The regulation of expression of bacterial genes  functioning in the absence of active cell growth was studied on the model of microcin C51 operon. It is shown that the expression of the operon is activated when  E. coli cells passed in the stationary phase of growth, and implemented with the participation of the complex regulatory network including  four global transcription regulators. The detailed analysis and site-directed mutagenesis of the promoter region of the microcin operon has been performed and sites essential to the regulation of expression of the operon have been determined.
 
III.  Quorum Sensing (QS) regulation of gene expression of bacteria: molecular, genetic and functional investigations, role in the regulation of cell processes ( 2003 -  at present time ).
The ability to synthesize autoinducers of Quorum Sensing (QS) systems of regulation of gene expression of bacteria N-acyl-homoserine lactones (AHL) in more than 200 strains of soil-born and rhizosphere pseudomonads isolated in various geographic zones was studied; AHL synthesis was observed in 17% strains investigated.
QS systems of model strains  Pseudomonas chlororaphis, Burkholderia cenocepacia, Serratia proteamaculans were studied in details. Genes of QS systems have been cloned and sequenced, their organization was defined, the role of global transcription regulators in the control of the expression of  QS systems genes was explained. The data on the role of QS systems in the regulation of cellular processes of bacteria have been  obtained.
The stimulating action of subinhibitory concentrations of nitrofurans, NO donors, plant phenolic compounds, some phytohormones, including salicylic acid, and hydrogen peroxide on the bacterial biofilms formation  have been shown. In the case of the action of phenols and hydrogen peroxide this effect was associated with QS regulation of bacterial genes expression. As the concentrations of these compounds increase they inhibited the formation of biofilms. The results  obtained are important for medicine because pathogenic bacteria living in biofilms are much more resistant to the action of antibacterial agents than planctonic bacteria. Therefore, data on biofilm formation stimulation by low concentrations of antibacterial agents must be considered in defining of schemes of antibacterial therapy using preparations containing these compounds or their derivatives.
 
IV.  Volatile organic compounds (VOC), synthesized by bacteria: nature,   action on various biological objects, mechanisms of action, functional role (2011-at present time).
The synthesis of volatile organic compounds (VOCs)  by  Pseudomonas and Serratia strains was studied, the individual VOCs  were identified (in collaboration with Dr. L. Chernin, Jerusalem University, Israel). It was shown that total pools of volatiles and individual VOCs (dimethyldisulfide, ketones)  suppressed the growth of phytopathogenic bacteria and fungi, cyanobacteria, bacterial biofilms formation.  They could also exert a lethal effect on insects (Drosophila) and nematodes.
It was shown for the first time that VOCs inhibit functioning of QS regulation systems of bacteria.
 
V.  Interactions of metal nanoparticles with bacterial cell. Biogenesis of nanoparticles using bacterial cultures ( 2009  – at present time).
The action  of silver and gold nanoparticles and ions on the growth, viability of bacteria  and on bacterial biofilms was studied.
 Mutations in genes responsible for the repair of DNA containing oxidative lesions were shown to increase the sensibility of  E. coli cells to silver nanoparticles and silver ions. This suggests that these genes may be involved  in the repair of damaged DNA caused by silver ions and  nanoparticles.
The data about the important role of transport proteins porins in antibacterial effect of silver nanoparticles have been obtained.
The experiments on obtaining nanoparticles of gold  by "green synthesis" in cultures of cyanobacteria and Azotobacter were performed; the importance of the process of nitrogen fixation for the biogenesis of nanoparticles have been established.