Preparation and properties of stretched polytene chromosomes. 2. Mechanism of stretching]

Isolated polytene chromosomes were stretched in a 0.125 M NaCl solution with constant speed, by constant force and by cyclically changing force. For each regime, the dependence of chromosome length on the time and force magnitude were recorded. From this it may be concluded that three processes are involved in chromosome stretching: viscoelastic deformation, viscous flow of DNP segments, and cristallization, i.e. intermolecular cross-linking of neighbour segments. At a high rate stretching (V greater than Vo) chromosome may be torn like at small deformation; when rate is V greater than Vo chromosome deformation is mostly viscoelastic; at rates V approximately Vo viscous flow of DNP segments if predominant. We estimate Vo approximately less than 3--6 mum/s. Electron microscopy shows that during chromosome stretching its DNP fibers are oriented along chromosome axis without detectable breaks.     

Selection of a Microbial Community in the Course of Formation of Acid Mine Drainage

Microbiology - Changes in microbial community composition during formation of an acid mine drainage were studied on a model of two water reservoirs located in the Ozernoye open-cast mine for...     

Bioaugmentation of Anammox Activated Sludge with a Nitrifying Bacterial Community as a Way to Increase the Nitrogen Removal Efficiency

Microbiology - Bioaugmentation, i.e., increasing the abundance of certain microorganisms in the community by adding appropriate cells or establishing the conditions promoting their growth, is...     

An analysis of the patterns in the development of the initial period of the acute radiation bone marrow syndrome in man

Using a principally new approach, that is a mathematical analysis of the postirradiation neutrophilic curve, the authors have confirmed their previous assumption that the number of divisions that a granulocytic cell performs during the entire period of its maturation both in normal conditions and during the development of acute radiation sickness is virtually the same. D0 of early committed [correction of commitable] precursors of the granulocytic department is 1.6-1.7 Gy at n = 1.     

Effect of desiccation on tolerance of salmonella enterica to multiple stresses

Reducing the available water in food is a long-established method for controlling bacterial growth in the food industry. Nevertheless, food-borne outbreaks of salmonellosis due to consumption of dry foods have been continuously reported. Previous studies showed that dried Salmonella cells acquire high tolerance to heat and ethanol. In order to examine if dehydration also induces tolerance to other stressors, dried Salmonella enterica serotype Typhimurium cells were exposed to multiple stresses, and their viability was assessed. Indeed, desiccated S. Typhimurium acquired higher tolerance to multiple stressors than nondesiccated cells. The dried cells were significantly more resistant to most stressors, including ethanol (10 to 30%, 5 min), sodium hypochlorite (10 to 100 ppm, 10 min), didecyl dimethyl ammonium chloride (0.05 to 0.25%, 5 min), hydrogen peroxide (0.5 to 2.0%, 30 min), NaCl (0.1 to 1 M, 2 h), bile salts (1 to 10%, 2 h), dry heat (100°C, 1 h), and UV irradiation (125 μW/cm(2), 25 min). In contrast, exposure of Salmonella to acetic and citric acids reduced the survival of the dried cells (1.5 log) compared to that of nondesiccated cells (0.5 log). Three other S. enterica serotypes, S. Enteritidis, S. Newport, and S. Infantis, had similar stress responses as S. Typhimurium, while S. Hadar was much more susceptible and gained tolerance to only a few stressors. Our findings indicate that dehydration induces cross-tolerance to multiple stresses in S. enterica, demonstrating the limitations of current chemical and physical treatments utilized by the food industry to inactivate food-borne pathogens.     

Structural characterization of geranylgeranyl pyrophosphate synthase GACE1337 from the hyperthermophilic archaeon Geoglobus acetivorans

Extremophiles - A novel type 1 geranylgeranyl pyrophosphate synthase GACE1337 has been identified within the genome of a newly identified hyperthermophilic archaeon Geoglobus acetivorans. The...     

En masse lentiviral gene delivery to mouse fertilized eggs via laser perforation of zona pellucida

Lentiviruses are highly efficient vehicles for delivering genes into cells. They readily transduce primary and immortalized cells in vivo and in vitro. Genes delivered by lentiviruses are incorporated and replicated as part of their host genome and therefore offer a powerful tool for creation of stable cell lines and transgenic animals. However, the zona pellucida surrounding the fertilized eggs acts as a barrier and hinders lentiviral transduction of embryos. Here, we utilize a laser, typically used to perforate the zona pellucida for in vitro fertilization, to permeabilize the zona for lentiviral gene delivery. A single hole in the zona is sufficient for the lentivirus to gain access to fertilized eggs without the need for microinjection for en masse gene delivery. Embryos generated by this method elicit no damage and can develop to term for creation of transgenic animals.     

Effect of the length of internucleosome regions of DNA on the conformation of chromatid fibrils

Models of chromatin fibers structures with linear regions of linker DNA were analysed. Limitations put by end dimensions of linker DNA and nucleosomes are considered. Good agreement between the structural properties of model and real chromatin fibers was obtained. It has been shown that the models with three and more configurations of closely located nucleosomes have linker DNA of 19-53 base pairs length, which is characteristic of real chromatin of the majority of somatic cells.