Biosynthesis of selenium nanoparticles by potential endophytic fungi Penicillium citrinum and Rhizopus arrhizus: characterization and maximization

Abstract

AbstractFungal-mediated biosynthesis of selenium nanoparticles (SeNPs) is one of the promising biological-based nanomanufacturing process. On the other hand, the use of endophytic fungi in this respect has emerged as a new approach for green and cost-effective production of several nanoparticles. In the present study, two endophytic fungal isolates, identified as Penicillium citrinum and Rhizopus arrhizus morphologically and genetically using the ITS rRNA- gene. These fungal strains exhibited tolerance up to 40 mM NaSeO3 accompanied with red coloration of the medium that suggested selenite reduction and formation of selenium nanoparticles (SeNPs). The reduced selenite was quantified using inductively coupled plasma mass spectrometry (ICP-MS), and the results revealed that these fungi under the optimum growth conditions are able to transform > 99.0% of 3.0 mM selenite into elemental selenium. The crystalline structure, particle-sized distribution, and morphology of the purified selenium particles were extracted and characterized by different techniques including UV–Vis, X-ray diffraction and high-resolution transmission electron microscopy. The results indicated the production of regular spherical shapes of SeNPs with a majority of average size between 50 and 80 nm. Fourier transform infrared spectroscopy (FT-IR) of the produced particles revealed the presence of different functional groups that would be implicated in the synthesis process as bioreducers and capping agents. The results of optimum growth conditions revealed that the higher fungal growth resulted in the higher selenite reduction activity. Sabouraud’s and yeast extract-peptone-glucose (YPG) broth media are the best media for maximum growth of P. citrinum and R. arrhizus, respectively, and synthesis of SeNPs. The best carbon sources are sucrose and starch while NH4NO3 and NH4Cl are the best nitrogen sources for growth and synthesis of SeNPs by the fungal strains. Selenite reduction and biosynthesis of SeNPs by the fungi seemed to increase with increasing pH and maximized at alkaline pH value (9.0) being 97.94 and 97.13% for P. citrinum and R. arrhizus respectively. Initial selenite concentration markedly influenced SeNP production and the maximum rates were 96.94 and 98.47% recorded at 3.0 mM selenite for both fungi. In conclusion, the results were discussed in relation to the potentiality of these endophytic fungi for biosynthesis of SeNPs, and the favorable nutritional conditions for maximum production.