Genomic features of metal-resistant bacteria suitable for tannery effluent bioremediation

• Published in: Journal of water process engineering 2024-12, Vol.68, p.106406, Article 106406
• Main Authors: Lejri, Rokaia, Mekki, Ali, Ellafi, Ali, Henchiri, Selma, Giner Tarazón, Joel, Valero Tebar, Juan, D'Auria, Giuseppe, Chamkha, Mohamed, Chaieb, Mohamed, Džunková, Mária, Ben Younes, Sonia
• Format: Article
• Language: English
• Subjects: Bioremediation; Cytotoxicity; Heavy metals; Minimal bactericidal concentration; Minimal inhibitory concentration; Phytotoxicity; Tannery effluents; Whole-genome sequencing
• ISSN: 2214-7144; 2214-7144
• DOI: 10.1016/j.jwpe.2024.106406

Biological treatments are widely used to manage tannery wastewater, but their effectiveness depends on the specific conditions of each tannery, driving the continuous search for effective pollutant-degrading microbes. Nevertheless, only few of tannery microbes have their whole genome sequenced, which hinders exploring more effective bioremediation pathways. We analyzed genomes and bioremediation potential of seven Enterococcus faecium strains and two Bacillus licheniformis strains from the effluents of the Southern Tunisian tannery (ESTT). The strains were taxonomically classified by GTDB-tk and their metabolic potential was reconstructed using KEGG database, followed by the pan-genome analysis by Rotary pipeline. These strains possess novel genomic features and their genetic differences are not explicitly related to previously known bioremediation pathways. ESTT treated with either a combination of seven E. faecium strains and two B. licheniformis strains, or a mixture of all nine strains, showed no toxicity to plant seeds Triticum durum, Lens culinaris and blood cells. The combination of the nine strains resulted in a 1.85 ± 0.81-fold reduction in heavy metal concentration compared with that of mixtures of separate strains and a 3.94 ± 1.99-fold reduction compared with that of the untreated ESTT effluent. Furthermore, the strain mixture demonstrated a 3.9-fold reduction in chemical oxygen demand (COD), a 3.3-fold reduction in chlorine (Cl), a 2.16-fold reduction in biochemical oxygen demand (BOD5), and a 1.3-fold reduction in total organic carbon (TOC) relative to those of the untreated effluent. In conclusion, the utilization of strain mixtures for heavy metal reduction holds promise in meeting international environmental standards. [Display omitted] •Seven Enterococcus and two Bacillus strains were isolated from tannery effluents.•Whole genome analysis showed genetic differences between these new strains.•Strains possess exceptional abilities to reduce heavy metals.•The bioremediation abilities are not related to previously known bioremediation genes.•Strains show synergistic effect in bioremediation of tannery effluents.