Biosynthesis and antibacterial activity of gold nanoparticles coated with reductase enzymes

Potential of luminescent bacteria in production of metal nanoparticles (NPs) has not been well evaluated up until now. These bacteria contain lux operon which is included of reductase enzymes, by increasing bacterial cell density, the expression of aldehyde synthetic enzymes elevate and enhance the yields of NPs synthesis. Therefore, extracellular synthesis of gold NPs (AuNPs) using natural occurring luminescent bacteria, VLA, VLB, VLC and genetically engineered luminescent bacteria, Pseudomonas putida KT2440 and Pseudomonas fluorescence OS8 have been successfully conducted. NPs were characterised and their antibacterial activity evaluated using microtitre plates at different concentrations against some hospital pathogenic bacteria. Biosynthetic AuNPs produced had maximum absorption at the ranges of 500-550 nanometre wavelengths. Transmission electron microscopy images showed particle sizes between 10 and 50 nanometres and confirmed the success of purification process. The NPs were spherical and the FTIR analysis showed the existence of biomolecules on surface of purified NPs that could be most probably related to reductase enzymes that are stabilised on NPs surfaces. Further investigation on antibacterial properties of these novel NPs which coated by reductase enzymes showed that any increase or decrease in antibacterial activity is dependent on NPs concentration.