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DEPARTMENT OF BIOLOGICAL SYSTEM
PHYSICS
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Thermal properties of complex heterogeneous biological systems
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Thermal properties of biological systems ( bacterial cultures and plant roots) are studied by the high- and
low-temperature calorimetry.
a) The differential scanning microcalorimetry study of heavy metalls impact on the
thermostability of bacterial cells.
The study aims to analyze the thermostability of bacterial cell population following life-threatening
treatments ( toxic metals ) and to identify the initial intracellular critical targets of toxic impact for cell
survival or death applying the differential scanning calorimetry method to provide the suitable thermal
analysis technique for the time efficient estimation of the toxicity and the determination of its
development at long-term treatment on the whole bacterial population level. Special and general stress-
responses of bacterial cells to multiple stresses cause alterations in gene expression and protein activity.
Thermostability could characterize the structural and physiological properties of a bacterial cell. When a
multicomponent object like a cell is heated, there occurs a sequence of transitional effects that cause
perturbation to the specific heat capacity of the cell. Differential scanning calorimetry (DSC) method, a
thermal-analysis technique, senses these perturbations and records them as a characteristic pattern of
transitions representing various cellular components. DSC measures the excess specific heat in a
continuous manner as a function of increasing temperature at a fixed scan rate.
The thermal spectra (temperature dependence of the heat capacity of the sample) are studied by the
modified serial calorimeter (ДАСМ-4М). The modification includes the fundamental changes in the
construction of measurement ampoules, partial change of electronic part and change of registering system
to digital registering. We developed special software for information collecting and processing of the
results. Also the LabView and Origin programs are used for the data processing.
We have used the DSC method to study the effect of hexavalent chromium (Cr(VI), recognized as human
carcinogen and environmental pollutant (International Agency for Research on Cancer, European Union),
on the soil bacteria Arthrobacter oxydans supposed to have high potential for heavy metals
detoxification. The thermal analysis demonstrated that thermograms of A. oxydans at non-toxic threshold
chromium concentrations changed in the form and intensity within the temperature range of
40-90 0C
reflecting the melting process of the intracellular structural cell components and did not influence the
DNP complex of the studied bacteria.The study was supported by the ISTC grant G-348.The DSC
technique was also applied to the study of the impact of the toxic oxidant potassium permanganate on a
bacterial cell culture. The changed pattern of thermal spectra of A. oxydans at permanganate treatment,
the measurement of the total heat capacity, and the temperature of the DNP complex demonstrated the
possibility to verify the permanganate impact on dependence of concentrations value and to characterize
the intracellular sequence events in response to toxic agent action, which initiates either a
stress-adaptation-survival response or cell death, depending on the severity of the insult.
The main objectives of the research combining the methods of differential scanning
microcalorimetry and the classical bacteriological methods are: 1) to estimate the concentration
boundaries of time-dependent Ni toxicity in different growth conditions (biofilms and planctonic cells) of
soil bacteria Arthrobacte oxydans cultures; 2) to evaluate the influence of Ni nontoxic and toxic doses on
thermal spectra of the bacterial cells; 3) to evaluate Ni impact (at non-toxic and toxic concentrations) on
cell metabolism (energy-dependence, respiration), 4) to study the interaction between the bacterial cell
surface and the water in the presence of toxic and nontoxic doses of Ni (supported by the GNSF grant №
979/07, 076186-230, code № 7/6-240, "The Application of the Calorimetry Methods to the Study of Ni
Toxic Impact on Bacterial Cells in Various Growth Conditions").
The results of these studies will allow us to use the calorimetric method for the obtaining the
parameters of efficient bacterial cells thermal inactivation and to detect the impact of the environmental
pollutants on the heat resistance of the selected studied bacteria. We plan to increase the types of bacteria
and increase the time of their interaction with the heavy metals, as the impact of metals on living
organisms in real situations is quite long.
Team leader: : Dr. Nugzar Bakradze, the principal investigator
Team members:Dr.E. Kiziria, the prin. ivest., Dr. M.Abuladze, the sen. res., V Sokhadze, the sen. res.,
E. Namchevadze, the res., Sh. Gogichaishvili, the res., G Tvauri. the res., L.Tabatadze, inj., L.Lejava, inj.
b) Water crystallization processes in plants.
In past years we were studying the peculiarities of water crystallization process in plant tissues, in relation
to the plant adaptation to the extreme environmental conditions. The results that we obtained reflect the
crystallization mechanisms of plant tissue intracellular water and the dependence of the water
supercooling on the changes in environment temperature. More recently we developed the laboratory
model of the low-temperature calorimeter, which is based on the utilization of modern technologies. This
device was used for the research of water crystallization process in the root tubercles of plants,
containing nitrogen-fixing bacteria. Unlike all other low-temperature scanning differential
microcalorimeters known to us (Perkin Elmer DSC, Setaram, TA Instruments Q2000), which use one or
another refrigerant in order to achieve low temperatures, the work of our microcalorimeter is based on the
use of semiconducting thermoelements (Cryotherm, St. Peterburg, Russia), the cold-productivity of which
is quite high (50 - 60 W). The LabView and Origin programs are used for the data processing.
The main objectives of the research are: water phase transition study in plantain roots (Plantago maior L.),
which were used as a model system to research the peculiarities of water crystallization and ice
melting in complex heterogeneous biological systems.
Team leader: : Dr. Nugzar Bakradze, the principal investigator
Team members:Dr.E. Kiziria, the prin. ivest., V Sokhadze, the sen. res.,
E. Namchevadze, the res., Sh. Gogichaishvili, the res.,
G Tvauri. the res.
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