ABSTRACT
Continued widespread use of antibiotics, especially fluoroquinolones, raises environmental concerns, as its driving bacterial resistance and disrupts microbial ecosystems. Here we investigate the biodegradation of ten fluoroquinolone antibiotics (six for medical use and four for veterinary use) by ligninolytic fungi, including Trametes versicolor, Bjerkandera adusta, Porosterum spadiceum, Irpex lacteus, Pleuroteus ostreatus, Phanerochaete chrysosporium, Pycnoporus cinnabarinus, Ganoderma lucidum, and Gloeophyllum trabeum. The results show significant variations between strains in the efficiency of antibiotic transformation. B. adusta and P. spadiceum were the fungi that most efficiently reduced antibiotic concentrations and were able to totally degrade eight and six antibiotics, respectively, within a 15-day period. T. versicolor and P. ostreatus also showed the ability to effectively degrade antibiotics. Specifically, T. versicolor degraded six out of the ten fluoroquinolone antibiotics by more than 70 %, while P. ostreatus degraded the tested antibiotics between 43 % and 100 %. The remaining antibiotic activity did not always correlate with a reduction in antibiotic concentrations, which points to the presence of post-transformation antimicrobial metabolites. This study also explores the potential mechanisms used by these fungi to remove selected models of fluroquinolones via enzymatic routes, such as oxidation by laccases, heme-peroxidases, and cytochrome P450, or via adsorption on fungal biomass.
ABSTRACT
An immobilized enzyme could exhibit selectively modified physicochemical properties, and it might offer a better environment for the enzyme activity. In this study, the immobilization yield of crude Halomonas sp. lipase was optimized to improve its stability. Thanks to its high adsorption capacity, CaCO3 has been chosen as support for the immobilization process. Furthermore, response surface methodology (RSM) was used to determine optimal conditions for the immobilization of the bacterial lipase. Five tested factors (enzyme solution, support amount, time, temperature, and acetone volume) were optimized applying a central composite design of RSM. The maximum yield of lipase immobilization was improved to 96%. Furthermore, a biochemical characterization proved a significant improvement of the immobilized lipase stability. The immobilized enzyme is more stable at extreme pH values and high temperatures than the free one. We also tested the reusability of the immobilized lipase by evaluating the recovery of the support using simple filtration. Thanks to its high stability, the immobilized lipase was invested in an effective treatment of tuna wash processing wastewater. The oil biodegradation efficiency was established at 81.5% and was confirmed by Fourier transformation infrared spectrometry. Likewise, the biological oxygen demand values were reduced which makes a possible reduction of the wastewater pollution degree.
