Heavy metal tolerance of microorganisms isolated from wastewaters: Identification and evaluation of its potential for biosorption

The aim of this study was to select autochthonous microorganisms that are able to biosorb heavy metals in aqueous systems. Forty-eight strains, included fungi, yeasts and bacteria, were isolated from water and sludge samples from urban and industrial wastewater treatment plants in the province of Jaen, southern Spain. Purified isolates were screened on the basis of their resistance to Pb(II), Zn(II) and Ag(I). Ten strains were selected and identified by molecular techniques. Tolerance index and minimum inhibitory concentration (MIC) for the three metals were also determined. It can be noted that tolerance of the strains appears to be associated with the sites of their isolation. The best results were obtained for the yeast Trichosporon sp. 4S3 which showed the following MICs: 32-35 mM for lead, 16-18 mM for zinc and 3-5 mM for silver. The use of native strains can be an interesting alternative for bioremediation processes of heavy metals. This study increases the number of microbial strains that have the ability to resist relatively higher concentrations of metals, which may make them recommendable as potentially low-cost biosorbents. The nucleotide sequences of all the selected isolates were deposited in GenBank, which could be of great interest for other investigators as reference strains in bioremediation processes of heavy metals. (C) 2012 Elsevier B.V. All rights reserved.