Industrial synthetic dyes cause health and environmental problems. This work describes the isolation of 84 bacterial strains from the midgut of the Lasius niger ant and the evaluation of their potential application in dye bioremediation. Strains were identified and classified as judged by rRNA 16S. The most abundant isolates were found to belong to Actinobacteria (49%) and Firmicutes (47.2%). We analyzed the content in laccase, azoreductase and peroxidase activities and their ability to degrade three known dyes (azo, thiazine and anthraquinone) with different chemical structures. Strain Ln26 (identified as Brevibacterium permense) strongly decolorized the three dyes tested at different conditions. Strain Ln78 (Streptomyces ambofaciens) exhibited a high level of activity in the presence of Toluidine Blue (TB). It was determined that 8.5 was the optimal pH for these two strains, the optimal temperature conditions ranged between 22 and 37 °C, and acidic pHs and temperatures around 50 °C caused enzyme inactivation. Finally, the genome of the most promising candidate (Ln26, approximately 4.2 Mb in size) was sequenced. Genes coding for two DyP-type peroxidases, one laccase and one azoreductase were identified and account for the ability of this strain to effectively oxidize a variety of dyes with different chemical structures.

Department of Biochemistry and Molecular Biology B Faculty of Medicine and LAIB IMIB University of Murcia 30100 Murcia Spain

Department of Microbiology and Genetics University of Salamanca Plaza Doctores de la Reina s n 37007 Salamanca Spain Spanish Portuguese Institute for Agricultural Research Salamanca Spain

Department of Microbiology and Genetics University of Salamanca Plaza Doctores de la Reina s n 37007 Salamanca Spain Spanish Portuguese Institute for Agricultural Research Salamanca Spain Institute of Microbiology Academy of Sciences of the Czech Republic Videnska 1083 142 20 Praha 4 Prague Czech Republic

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