Bioleaching is a technology that uses specific bacteria to extract valuable metals from minerals. The advantages of this technique over traditional methods (chemical leaching) include low cost, high efficiency and environment friendliness. Bioleaching allows to recovers metals from low grade ores at conditions where traditional techniques are not efficient and then, mining waste can be valorized and the impact on the environment is reduced. Chalcopyrite (CuFeS2) is the most abundant of the copper sulfides but at the same time, it is the most refractory too. The main microorganisms involved in the bioleaching of sulfide minerals are iron- and sulfur-oxidizing bacteria (Rawlings 2002). In the bioleaching process the ion Fe3+ plays an important role since it assists the process oxidizing the ore (Dorado et al. 2012). As a result, ferric iron is reduced to ferrous iron and then, the bacteria catalyze the cyclic regeneration of ferrous to ferric to promote continuous leaching of the sulfide mineral. However, Fe3+ ions have a low solubility and they can lead to the precipitation of iron (III) hydroxides and other ferric complexes such as jarosite, depending on the impurities of the mineral and the mineral medium used to keep the biological activity. The precipitation affects negatively the mass transfer process and it causes the decrease in the extraction yield of the metal (Zhang et al. 2008). Moreover, the presence of precipitates makes the optical methods of monitoring not suitable for controlling the process. In this case, the use of microrespirometry allows the monitoring of biomass growth by means of low sampling volume (<1mL) and high precision. Additionally, negative effects over the activity of microorganisms can be detected immediately and corrected. In this work, the microrespirometry was used to evaluate the effect of the mineral medium composition in the bioleaching of copper from a chalcopyrite ore. The microbial consortium was obtained from a biotrickling filter treating high loads of H2S and the copper extraction efficiency was monitored by atomic absorption. As an example, Figure 1 shows the evolution of the respirometric rates at different moments along the experiment.