1. Group of Environmental Biotechnology and Engineering, Department of Chemical Engineering. University of Santiago de Compostela. Rúa Lope Gómez de Marzoa, s/n. 15782 Santiago de Compostela, Spain. Phone: 0034 981563100, ext: 16740; Fax: 0034 981528050; E-mail: alvarezr@usc.es
2. Department of Ecology, Genetic and Microbiology, Faculty of Biology, University of León 24071, León, Spain.