Laccases are industrially relevant enzymes that have gained great biotechnological importance. To date, most are of fungal and mesophilic origin; however, enzymes from extremophiles possess an even greater potential to withstand industrial conditions. In this study, we evaluate the potential of a recombinant spore-coat laccase from the thermoalkaliphilic bacterium Bacillus sp. FNT (FNTL) to biodegrade antibiotics from the tetracycline, β-lactams, and fluoroquinolone families. This extremozyme was previously characterized as being thermostable and highly active in a wide range of temperatures (20–90 °C) and very versatile towards several structurally different substrates, including recalcitrant environmental pollutants such as PAHs and synthetic dyes. First, molecular docking analyses were employed for initial ligand affinity screening in the modeled active site of FNTL. Then, the in silico findings were experimentally tested with four highly consumed antibiotics, representatives of each family: tetracycline, oxytetracycline, amoxicillin, and ciprofloxacin. HPLC results indicate that FNTL with help of the natural redox mediator acetosyringone, can efficiently biodegrade 91, 90, and 82% of tetracycline (0.5 mg mL⁻¹) in 24 h at 40, 30, and 20 °C, respectively, with no apparent ecotoxicity of the products on E. coli and B. subtilis. These results complement our previous studies, highlighting the potential of this extremozyme for application in wastewater bioremediation.

Laccases are industrially relevant enzymes that are known for the wide variety of substrates they can use. In recent years, fungal laccases have been progressively replaced by bacterial laccases in applied contexts due to their capacity to work on harsh conditions including high temperatures, pHs, and chloride concentrations. The focus of researchers has turned specifically towards enzymes from extremophilic organisms because of their robustness and stability. The recombinant versions of enzymes from extremophiles have shown to overcome the problems associated with growing their native host organisms under laboratory conditions. In this work, we further characterize a recombinant spore-coat laccase from Bacillus sp. FNT, a thermoalkaliphilic bacterium isolated from a hot spring in a geothermal site. This recombinant laccase was previously shown to be very active and thermostable, working optimally at temperatures around 70–80 °C. Here, we showed that this enzyme is also resistant to common inhibitors, and we tested its ability to oxidize different polycyclic aromatic hydrocarbons, as these persistent organic pollutants accumulate in the environment, severely damaging ecosystems and human health. So far, the enzyme was found to efficiently oxidize anthracene, making it a compelling biotechnological tool for biocatalysis and a potential candidate for bioremediation of aromatic contaminants that are very recalcitrant to degradation.