Extracellular synthesis of gold nanoparticles using the marine bacterium Paracoccus haeundaensis BC74171T and evaluation of their antioxidant activity and antiproliferative effect on normal and cancer cell lines

[Display omitted] •The marine bacterium Paracoccus haeundaensis BC74171T can extracellularly reduce gold ions to gold nanoparticles.•Different parameters for the synthesis of gold nanoparticles were optimized.•The gold nanoparticles synthesized showed non-toxicity to human normal cell lines.•Gold nanoparticles have concentration-dependent antioxidant activity and an antiproliferative effect on cancer cell lines. Green chemistry is beneficial for the production of eco-friendly and stable nanoparticles using biological agents. The present study was performed to explore the potential of the marine bacterium Paracoccus haeundaensis BC74171T for the extracellular synthesis of gold nanoparticles (AuNPs). Cell-free supernatant-mediated AuNPs were characterized by different techniques and analyzed for their antioxidant activity and antiproliferative effect on normal and cancer cells. Visual observations indicated the formation of AuNPs by the development of a ruby red color and were confirmed by a UV–vis absorbance peak at about 535 nm. The synthesized AuNPs were spherical in shape and had an average size of 20.93 ± 3.46 nm, as determined by transmission electron microscopy and a dynamic light scattering particle size analyzer, respectively. From Fourier transform infrared spectroscopy, the interaction of functional groups was determined and the presence of biomaterial on the AuNP surface was confirmed. Concentration-dependent antioxidant activity of AuNPs was observed by the 2,2-diphenyl-1-picrylhydrazyl method. The AuNPs synthesized do not show growth inhibition on HaCaT and HEK293 normal cells, while they show concentration-dependent growth inhibition in the case of A549 and AGS cancer cells. Thereby, this study proves that AuNP synthesis using P. haeundaensis is a facile method and that the AuNPs synthesized are non-toxic to human cells, which indicates that they can be useful in biomedical applications.