kualawohkensis strain KW12, although originating from a hot spring with temperatures 68–69 °C, behaved like a mesophilic organism. Nevertheless, the growing cells, cell suspensions, and the cytoplasmic fraction of the cell-free extract all reduced Cr(VI) more efficiently at higher temperatures. The chromate-reducing APO866 nmr capability of TSB-6, in spite of its isolation from sediments with undetectable level of Cr(VI), is consistent with earlier reports of Bader et al. (1999), who had enriched chromium-reducing consortia from
a noncontaminated source under mesophilic conditions. There is growing evidence that such organisms reduce Cr(VI) by enzyme(s) having a completely unrelated primary physiological role (Ishibashi et al., 1990; Bader et al., 1999; Gonzalez et al., 2005). Vibrio harveyi nitroreductase NfsA has been shown to possess Cr(VI) reductase activity as a secondary function (Kwak et al., 2003). Our results show a decrease
in the absolute values of ROS with time of incubation even in the control cells. This is not unexpected as oxidative stress changes with the phase of aerobic growth of bacteria (Ihssen & Egli, 2004). However, at each time point of measurement, heat-induced TSB-6 cells had higher ROS than the control cells. Besides, higher quantity of ROS in the induced cells was accompanied by higher Cr(VI)-reducing activity. Our proteomic analysis showed that the heat-induced antioxidative stress response of TSB-6 cells resulted in the upregulation of some proteins
involved in cellular metabolism and C-X-C chemokine receptor type 7 (CXCR-7) protein folding. Heat adaptive response in B. cereus is known to involve in induction of several proteins including stress proteins and chaperones see more (Periago et al., 2002; Ventura et al., 2006). It is known that besides heat, salt, osmotic condition, ethanol, starvation, and even chromium (VI) compounds can generate oxidative stress in a microorganism through the production of ROS. Antioxidative stress response often involves a set of proteins common to different kinds of stress. Cross-adaptation to heat and salt stresses has been demonstrated (Völker et al., 1992). Some of the proteins upregulated in heat-stressed TSB-6 are known to be associated with metabolism of carbohydrates, nucleotides, amino acids, lipids, vitamins, and energy. Transaldolase is a rate-limiting enzyme in the nonoxidative branch of pentose phosphate pathway, which generates NADPH in bacterial cells (Reitzer et al., 1980). Transaldolase catalyzes the reversible transfer of a dihydroxyacetone moiety from fructose-6-phosphate to d-erythrose-4-phosphate, thus forming d-sedoheptulose-7-phosphate and releasing d-glyceraldehyde-3-phosphate (Vatanaviboon et al., 2002). In bacteria, soluble oxidoreductases are possibly involved in the electron transport chain and oxidative stress response (Onyenwoke et al., 2009). It has been proposed that quinine oxidoreductases prevent the formation of potentially toxic semiquinone radicals and ROS (Gonzalez et al., 2005).