1 The influence of pH and temperature on the enzymatic activity of acidophilic heterotrophic microorganisms of the genus Acidiphilium Carmen Madalina Cismasiu 1 Keywords: extremophiles, acidophilic bacteria, bioremediation, acid mine drainage Introduction The study of acidophilic microorganisms has gained increasing importance due to their adaptations to cope with extreme environments (Baker & Banfield 2003, Johnson & Hallberg 2005) but also due to their biotechnological applications in bioremediation of polluted areas or metallic ions recovery from low-grade ores and wastewater mine drainage (Johnson 2003, Johnson & Hallberg 2003). The ability of these microorganisms to adapt to various environmental conditions is extremely useful also for their use in the biosorption of metals from acidic mining effluents (Carlson 1998, Johnson 1998). The tolerance of acidophilic bacteria to low pH (1- 4) is the result of their adaptation, these species being able to maintain their cytoplasm pH near the neutral value (Matzke et al., 1997). Their enzymatic activity is influenced by the acidity and temperature levels (Norris & Johnson 1998, Gupta et al. 2003); on their turn, through their metabolic activity, the acidophilic bacteria modify the oxide-reduction potential of the environment (Cismasiu 2001, 2004, Cismasiu et al. 2004) Acidiphilium is a genus, belonging to Eubacteria, phylogenetic division -Proteobacteria, order Acetobacteraceae; its physiology is close to Acidocella, the two genera being frequently isolated from the same acidic habitats (Cismasiu 2004). Due to its heterotrophic nutrition, Acidiphilium has the possibility to develop in organic media (with different concentrations of proteins or sugars). As carbon source it uses many different carbohydrates such as: fructose, glucose, sucrose, maltose, cellobiose, xylose, starch and glycogen (Cismasiu et al. 2000, 2002, Dopson et al. 2003). The aim of the study was to identify new organisms able to cope with the extreme environmental conditions from the mining areas and to isolate them in order to study their bioremediation potential. After isolating more strains from the acid effluents of the Ilba mining area (Maramureş, Romania), identified according to the morphological and physiological characteristics as being part of Acidiphilium genus (Cismasiu 2008), the study focused on their metabolic activity. Since Acidiphilium is both a mesophilic and acidophilic microorganism, the influence of temperature and pH on its enzymatic activity was investigated. This paper presents the influence of these two parameters on the amylolitic activity of Acidiphilium; starch was selected as a substrate, representing both the carbon and the energetic source. Material and Methods Ilba mining area is located in the Northern part of Romania, near the border with Hungary and Ukraine, in Maramures county (Fig.1); although the mine was closed in 2001, acidic wastewaters still represent an environmental threat, especially due to their low pH and high heavy metals content, leading to the degradation of local terrestrial and aquatic habitats. 1 Institute of Biology, Romanian Academy, Splaiul Independentei no. 296 sect.6, RO-060031 Bucharest, Romania. e- mail: madalinabio@yahoo.com