Biosynthesis, characterization and synergistic effect of phytogenic gold nanoparticles by marine picoeukaryote Picochlorum sp. in combination with antimicrobials

Abstract

In the present work, gold nanoparticles (Au-NPs) have been successfully synthesized by the marine picoeukaryote, Picochlorum sp. The alga culture was used as a reductant for HAuCl4·3H2O resulting in the phytosynthesis of Au-NPs within 48 h. The algal biomass turned purple in color due to the phytogenic Au-NPs at intracellular level. The phytogenic Au-NPs are characterized by surface plasmon band observed close to 520 nm; the phytogenic Au-NPs accumulated in plastids with an average size of 11 nm. The strong signals of gold were reported in their corresponding EDX spectra. FTIR analysis revealed that polysaccharide and protein biomolecules in the algae cell do dual function of reducing the Au3+ ions and stabilizing the phytogenic Au-NPs. In combination with ampicillin (10 µg), gentamicin (10 µg), amphotericin B (25 µg), the phytogenic Au-NPs exerted an outstanding antimicrobial effect and biocidal action against the tested Gram-positive, Gram-negative bacteria and the tested fungal pathogens. This study suggested that the different bioactive compounds reported in the FTIR profile of the phytogenic Au-NPs along with the presence of different fatty acids may play an important role in the synergistic antimicrobial effect of the phytogenic Au-NPs produced by Picochlorum sp. These results not only provide a green approach for the synthesis of Au-NPs but also open a door for new pharmaceutical leads.