Alejandra Arévalo-Gallegos, J Saul Garcia-Perez, Danay Carrillo-Nieves, RA Ramirez-Mendoza, Hafiz MN Iqbal, Roberto Parra-Saldívar

Microalgae produce metabolites with notable potentialities to act as reducing and capping agents for the synthesis of silver nanoparticles (AgNPs) in a process widely recognized as an eco-friendly and cheaper alternative for the generation of nanoparticles (NPs). In the present work, AgNPs were synthesized using live Botryococcus braunii cultures. Two biosynthesis routes were explored: (1) intracellular and (2) extracellular at pH levels of 6-9 using 1-5 mM silver nitrate concentrations. The generation of NPs was confirmed via ultraviolet-visible spectroscopy. The morphological characteristics were observed using scanning electron microscopy which revealed that the newly developed AgNPs were mostly spherical in sizes starting from 168 nm. The characteristic peaks in a typical Fourier transform infrared spectroscopy suggested that the exopolysaccharides were the possible reducing and capping agents. The antimicrobial spectrum of the newly developed AgNPs was tested against bacterial strains, both Gram-negative, Gram-positive, and yeast, ie, Escherichia coli (American Type Culture Collection [ATCC] 25922), Pseudomonas aeruginosa (ATCC 27853), Staphylococcus aureus (ATCC 25923), and the yeast Candida albicans (ATCC 10231), respectively. The antimicrobial activity tests showed a stronger inhibition against Gram-negative bacteria. Statistically, the NPs biosynthesized at pH values of 6 and 8 displayed a higher antimicrobial activity. Our findings showed that B. braunii is capable of generating AgNPs with antimicrobial potential.