Thermal analysis of whole bacterial cells exposed to potassium permanganate using differential scanning calorimetry: a biphasic dose-dependent response to stress.

The DSC technique applied to the study of the toxic impact of permanganate on bacterial cell culture detected the lack of linearity in the dose-response effect. The results were confirmed by the traditional assay of colony forming ability. The changed pattern of thermal spectra of A. oxydans at permanganate treatment, the measurement of the total heat capacity and the temperature of DNP complex demonstrate the possibility to verify the toxic impact in dependence of concentrations value.

Effects of Cr(VI) long-term and low-dose action on mammalian antioxidant enzymes (an in vitro study).

In order to investigate the low-dose long-term Cr(VI) action on antioxidant enzymes in cultured mammalian cells we estimated the activity of glutathione dependent antioxidant enzymes, catalase and superoxide dismutase (SOD) under various chromium concentrations in human epithelial-like L-41 cells. The long-term action of 20 microM causes the toxicity that results in losing of the cell viability by activating the apoptotic process, as identified by morphological analysis, the activation of caspase-3, and DNA fragmentation. The toxic chromium concentration totally destroys glutathione antioxidant system, and diminishes the activity of catalase and cytosolic Cu, ZnSOD. The non-toxic concentration (2 microM) causes the activation of the antioxidant defense systems, and they neutralize the oxidative impact.

A calorimetric characterization of Cr(VI)-reducing Arthrobacter oxydans at different phases of the cell growth cycle.

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 degrees C, we observed that spectral changes are particularly significant in the 40-90 degrees 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 degrees C region are less pronounced, implicating that the structural composition of DNA-Protein (DNP) complexes may change little.