Nazira S. Karamova

SOS-inducing ability of native and mutant microbial ribonucleases

The results of genotoxicity testing of microbial ribonucleases from Bacillus species with different catalytic activity obtained by site-directed mutagenesis in SOS chromotest are reported. At the concentrations 0.1-1 mg/ml, the induction factor for wild-type bacillar binase, barnase and mutant Arg58Lys binase with 100% activity was found to be significantly higher than 1.5 (1.8-2.8). Mutant RNases having decreased catalytic activity (binases with replacements Lys26Ala, Arg61Gln, His101Glu) or through natural inhibitor barstar inactivated wild-type RNase exhibited no SOS-inducing potency. The ability of native bacillar RNases and mutant enzymes possessing high catalytic activity comparable with the activity of wild-type RNase to cause the SOS response indicates that genotoxicity is mediated through the probable cleavage of cellular RNA.

Genotoxicity of bacterial ribonuclease in mammalian cells after its application in vitro and in vivo

Binase is an abbreviated name of guanylspecific small RNase produced and secreted by Bacillus intermedius. It is a single chain protein with 109 amino acids and no disulphide briges [1]. Binase shows marked specificity towards purine bases of polynucleotides and dinucleoside-phosphates and is guanyl-specific in reaction with nucleoside-2’3’-cyclophosphates [2].

The Effect of high hydrostatic pressure on the viability and mutagenesis of Salmonella typhimurium

This work is devoted to the study of the influence of high hydrostatic pressure (HHP) on the viability and level of mutagenesis of Salmonella typhimurium. It was established that the viability of bacteria significantly decreases under hydrostatic pressure of 200 MPa or higher. In addition, the viability index of the bacteria is six orders of magnitude lower with respect to the number of colony-forming units (CFUs) compared to the data of the flow cytofluorometry analysis. This is probably due to the transition of some part of the bacterial population to a viable but nonculturable state (VBNC). HHP of 50 MPa caused a 1.9-fold increase in the number of His+ revertants of the S. typhimurium strain TA98, which indicates the potential of the induction of gene mutations under these conditions. The mechanisms to reduce the viability and genetic changes in bacterial cells under HHP conditions are discussed.