Arthrobacter species is of interest because of its high potential for bioremediation. Bacteria can detoxify chromium, by either reduction or accumulation inside the bacteria and/or absorption of chromium(VI) (CrVI) on their surface, and efflux pump. The possible pathway of Cr(VI) reduction by Arthrobacter oxydans isolated from Columbia basalt rocks at a US DOE highly contaminated site (USA) has been considered in the present study. FTIR absorption spectroscopy showed that these bacteria reduce Cr(VI). In the present study the threshold Cr(VI) nontoxic concentration (35 microg/mL) for A. oxydans growing in liquid medium was estimated. Complete uptake of this concentration was achieved in about 10 days after chromium addition into the medium. At this concentration an increase in the protein isolated from the cell wall of A. oxydans was observed. This increased protein predominated independently of the growth phase at which Cr(VI) was added. Thermal analysis was used to identify any influence of Cr(VI) on the DNP complex of A. oxydans. According to the data obtained it can be supposed that Cr(VI) reduction predominantly occurs on the bacterial surface and that cell wall represents a permeable barrier for these bacteria at the non-toxic chromium action.

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Differential scanning calorimetry (DSC) was applied to estimate the impact of the toxic oxidant potassium permanganate (PM) on the intracellular structural and functional alterations at whole cell level using soil bacteria Arthrobacter oxydans as a model culture. Differential scanning calorimetry (DSC) was applied in order to estimate the impact of the toxic oxidant potassium permanganate (PM) on the intracellular structural and functional alterations at the whole cell level using the soil bacteria Arthrobacter oxydans as a model culture. We compared the total melting heat and the temperature of DNA-protein complex (DNP) melting at the PM application prior to the calorimetry measurement and after 24-h exposure at the concentration range 0.02–1.4 mM. The initial oxidative effect caused changes in the pattern of the whole cell melting spectra (mainly at the temperature range 56–78°C), the decrease of Tmax °C DNP melting, and did not influence significantly the total heat of bacterial melting at different concentrations of PM. The prolonged effect of permanganate up to 24 h was characterized by a biphasic dose-dependent response to stress estimated by the DSC technique and the colony-forming assay. The low doses of PM (0.02 and 0.2 mM) stimulated cell proliferation, and increased the total whole cell melting heat and the temperature of DNP melting. The toxic effect of PM up to 0.04 mM reduced cell viability, changed the character of multipeaked thermograms, and lowered the total melting heat and the temperature of DNP melting in a concentration-dependent manner. This study presents the DSC method for evaluating and monitoring the effects of exposure to potential human and environmental toxicants.

This is the first of a series of calorimetric studies designed to characterize and understand survival mechanisms of metal-reducing bacteria isolated from metal-polluted environments. In this paper we introduce a new concept of thermal spectrum of the endothermic melting of complex biological systems (e.g., proteins, nucleic acids, ribosomes, membrane structures) in intact cells. All thermal spectra measured are thermograms that describe the temperature dependence of heat capacity change of the complex systems of biologically active substances in bacterial cells. This new concept of thermal spectrum was applied to investigate spectral features from intact cells of Cr(VI)-reducer Arthrobacter oxydans at different points of their growth conditions and stages. Over the temperature range of 40–105°C, we observed that spectral changes are particularly significant in the 40–90°C interval. This may correspond to the orderly changes in subcellular structural elements: proteins, ribosomes and RNA, membranes, and various structural elements of the cell wall during different points of the growth cycle and growth conditions. Spectral changes in the 90–105°C region are less pronounced, implicating that the structural composition of DNA-Protein (DNP) complexes may change little.