FB 55 01.indd

Acidithiobacillus ferrooxidans (A. ferrooxidans, formerly Thiobacillus ferrooxidans) is the Gram-negative, acidophilic, chemolithoautotrophic bacterium that obtains its energy from the oxidation of ferrous iron, elemental sulphur, or partially oxidized sulphur compounds (Leduc and Ferroni, 1994; Rohwerder et al., 2003), even hydrogen or formate in anoxic conditions (Drobner et al., 1990; Pronk et al., 1991). The ability of A. ferrooxidans to solubilize metal sulphides has been successfully applied in bioleaching operations (Tuovinen, 1990; Rawlings, 2002). However, little is known about the molecular basis underlying the microorganism’s perturbation response behaviour or the impact of environmental stresses (e.g., temperature upshift, pH fluctuations, presence of toxic heavy metals and nutrient limitation), which normally take place in bioleaching operations and may affect the bacteria activity (Tuovinen and Kelly, 1972; Brierley, 1978). Variation in growth temperature is a common stress encountered in nature and industrial application. The heat-shock response, which is elicited by a sudden increase in growth temperature, has been widely used as a model system for studying the impact of stress on biological systems (Mager and De Kruijff, 1995), such as Escherichia coli, Desulfovibrio vulgaris, Shewanella oneidensis and Campylobacter jejuni (Arsene et al., 2000; Stintzi, 2003; Gao et al., 2004; Zhang et al., 2006). The hallmark of this adaptive cellular response is that bacteria reduce the gene expression of most normal cellular proteins, inducing at the same time transient overproduction of a limited set of proteins, called heat-shock proteins (Hsps), which are also found to be involved in cellular response to many other stress conditions, such as puromycin and acid stress (Leverrier et al., 2004). Several Hsp families can be designated according to their average apparent molecular mass, e.g., Hsp100, Hsp90, Hsp70 (DnaK), Hsp60 (GroEL), and small Hsps. In addition, ATP-dependent proteases such as ClpP and Lon are known to be Hsps (Gottesman, 1996). In general, their main function in the cell is to mediate the correct assembly of some oligomeric proteins from their subunits (Nilsson and Anderson, 1991). Hsps also play important roles in protein folding, degradation and transport across membranes. Real-time PCR has become one of the most widely used methods for gene quantitative analysis (Marisa and