Research article Interactions of the metal tolerant heterotrophic microorganisms and iron oxidizing autotrophic bacteria from sulphidic mine environment during bioleaching experiments Sanja Jeremic a , Vladimir P. Be  skoski b, ** , Lidija Djokic a , Branka Vasiljevic a , Miroslav M. Vrvi  c b , Jelena Avdalovi  c c , Gordana Gojgi  c Cvijovi  c c , Latinka Slavkovi  c Be  skoski d , Jasmina Nikodinovic-Runic a, * a Institute of Molecular Genetics and Genetic Engineering, University of Belgrade, P.O. Box 23,11010 Belgrade, Serbia b Faculty of Chemistry, University of Belgrade, P.O. Box 51,11158 Belgrade, Serbia c Department of Chemistry, Institute of Chemistry, Technology and Metallurgy, University of Belgrade, P.O. Box 473,11001 Belgrade, Serbia d Vin ca Institute of Nuclear Sciences, University of Belgrade, P.O. Box 522,11522 Belgrade, Serbia article info Article history: Received 8 January 2016 Received in revised form 19 February 2016 Accepted 22 February 2016 Available online xxx Keywords: Heavy metals Biofilms Bioleaching Bioremediation Autotrophic iron oxidizing Acidithiobacillus sp abstract Iron and sulfur oxidizing chemolithoautotrophic acidophilic bacteria, such as Acidithiobacillus species, hold the dominant role in mine environments characterized by low pH values and high concentrations of reduced sulfur and iron compounds, such as ores, rocks and acid drainage waters from mines. On the other hand, heterotrophic microorganisms, especially their biofilms, from these specific niches are receiving increased attention, but their potential eco-physiological roles have not been fully understood. Biofilms are considered a threat to human health, but biofilms also have beneficial properties as they are deployed in waste recycling and bioremediation systems. We have analyzed interactions of the metal tolerant heterotrophic microorganisms in biofilms with iron oxidizing autotrophic bacteria both from the sulphidic mine environment (copper mine Bor, Serbia). High tolerance to Cu 2þ , Cd 2þ and Cr 6þ and the presence of genetic determinants for the respective metal tolerance and biofilm-forming ability was shown for indigenous heterotrophic bacteria that included strains of Staphylococcus and Rhodococcus. Two well characterized bacteria- Pseudomonas aeruginosa PAO1 (known biofilm former) and Cupriavidus metallidurans CH34 (known metal resistant representative) were also included in the study. The inter- action and survivability of autotrophic iron oxidizing Acidithiobacillus bacteria and biofilms of hetero- trophic bacteria during co-cultivation was revealed. Finally, the effect of heterotrophic biofilms on bioleaching process with indigenous iron oxidizing Acidithiobacillus species was shown not to be inhibitory under in vitro conditions. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Mining processes are producing large amounts of waste mate- rials still containing high amounts of valuable and in some cases toxic metals, that are usually deposited as waste dumps or tailings near mine areas (Schippers et al., 2000). Bioleaching is often a method of choice for remediation of heavy metal contaminations (Hashim et al., 2011). Iron and sulfur oxidizing chemo- lithoautotrophic acidophilic bacteria, such as Acidithiobacillus spe- cies, have the dominant role in bioleaching (Schippers et al., 2014). Environments characterized by low pH values and high concen- trations of reduced sulfur and iron compounds, such as ores, rocks and acid drainage waters from mines, represent prime niches of iron oxidizing Acidithiobacillus species (Kelly and Harrison, 1989). Most of the research on the microbiology of mines and mine tail- ings is focused mainly on this group of bacteria and their role in these ecological niches. Still, mine environments are inhabited with other indigenous bacteria that also have specific ecological roles. The evidence of the existence of heterotrophs in mines usually comes from the metagenomic studies (Bajkic et al., 2013; He et al., * Corresponding author. ** Corresponding author. E-mail addresses: vbeskoski@chem.bg.ac.rs (V.P. Be skoski), jasmina. nikodinovic@imgge.bg.ac.rs (J. Nikodinovic-Runic). Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman http://dx.doi.org/10.1016/j.jenvman.2016.02.041 0301-4797/© 2016 Elsevier Ltd. All rights reserved. Journal of Environmental Management 172 (2016) 151e161