Biotechnological Applications of the Ubiquitous Fungus Penicillium sp. 8L2: Biosorption of Zn(II) and Synthesis of ZnO Nanoparticles as Biocidal Agents

In this study, the capacity of the ubiquitous filamentous fungus Penicillium sp. 8L2 to remove Zn(II) ions present in synthetic solutions was studied and the optimal operating conditions were obtained based on a response surface methodology (RSM). The contact time was optimized through kinetic tests. Equilibrium tests were then carried out, which allowed biosorption isotherms to be obtained for several mathematical models. At the same time, the capacity of the fungal cell extract to transform metal ions into ZnO nanoparticles with a biocidal capacity was evaluated. Its inhibitory capacity for five microbial strains was then determined. The biosorption mechanisms and nanoparticle synthesis were characterized by different crystallographic, spectrophotometric and microscopic analytical techniques. It was confirmed that the metal was bound superficially but also in the periplasmic space with a strong bond to phosphate groups, both in the biosorption stage and during the synthesis and consolidation of the nanoparticles. In addition, the presence of hydroxyl, amino, carbonyl and methylene groups was identified, which could promote the synthesis of nanoparticles, since some of them have a reducing nature. The kinetics showed that the biosorption of Zn(II) occurred in two stages, the first very fast and the second slower. Equilibrium tests identified a maximum biosorption capacity of 52.14 mg/g for the Langmuir model under optimized conditions: a contact time of 5 days, pH 5.6 and a 0.2 g/L biomass dose. The success of the biological synthesis route was confirmed and ZnO nanoparticles with an average size of 18 nm were obtained. The data showed that the nanoparticles showed a good inhibition ability against the tested microorganisms, with values ranging from 62.5 to 1000 µg/mL. Penicillium sp. 8L2 is a promising ubiquitous microorganism in the field of heavy metal biosorption and applied biotechnology.