Extracellular synthesis gold nanotriangles using biomass of Streptomyces microflavus

Abstract

Applications of nanotechnology and nano-science have ever-expanding breakthroughs in medicine, agriculture and industries in recent years; therefore, synthesis of metals nanoparticle (NP) has special significance. Synthesis of NPs by chemical methods are long, costly and hazardous for environment so biosynthesis has been developing interest for researchers. In this regard, the extracellular biosynthesis of gold nanotriangles (AuNTs) performed by use of the soil Streptomycetes. Streptomycetes isolated from rice fields of Guilan Province, Iran, showed biosynthetic activity for producing AuNTs via in vitro experiments. Among all 15 Streptomyces spp. isolates, isolate No. 5 showed high biosynthesis activity. To determine the bacterium taxonomical identity at genus level, its colonies characterised morphologically by use of scanning electron microscope. The polymerase chain reaction (PCR) molecular analysis of active isolate represented its identity partially. In this regard, 16S rRNA gene of the isolate was amplified using universal bacterial primers FD1 and RP2. The PCR products were purified and sequenced. Sequence analysis of 16S rDNA was then conducted using National Center for Biotechnology Information Basic Local Alignment Search Tool method. The AuNTs obtained were characterised by ultraviolet-visible spectroscopy, atomic force microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction spectroscopy analyses. The authors results indicated that Streptomyces microflavus isolate 5 bio-synthesises extracellular AuNTs in the range of 10-100 nm. Synthesised SNPs size ranged from 10 to 100 nm. In comparison with chemical methods for synthesis of metal NPs, the biosynthesis of AuNTs by Streptomyces source is a fast, simple and eco-friendly method. The isolate is a good candidate for further investigations to optimise its production efficacy for further industrial goals in biosynthesis of AuNTs.

Fig. 1

Biomass of Streptomyces sp. isolate No. 5 in CG medium and colonies developed in it after 7 days

Fig. 2

Biosynthesised AuNPs in a colloidal dispersion by Streptomyces sp. isolate No. 5 a Colonies before b After exposure to HAuCl4 after 24 h

Fig. 3

UV–vis spectrometer of AuNPs produced by S. microflavus isolate No. 5. After reactions with the S. microflavus isolate No. 5 for 24 h. Presence of a strong peak with maximum absorbance at 550 nm is prominent

Fig. 4

XRD pattern of AuNPs biosynthesised by S. microflavus isolate 5

Fig. 5

EDX pattern for S. microflavus isolate 5. indicating strong signals for presence of elemental gold in the sample

Fig. 6

AFM images of AuNTs synthesised by S. microflavus isolate No. 5 indicative of presence of spherical and triangular AuNPs a 1D b 3D

Fig. 7

TEM analysis a, b TEM micrograph recorded of an aqueous solution incubated with S. microflavus isolate No. 5 with Au⁺ ions for 24 h c Size distribution of the biosynthesised AuNPs deduced from TEM micrographs

Fig. 8

FTIR spectrum for S. microflavus isolate No. 5 showing peaks at different regions. These peaks are related with specific bonds

Fig. 9

SEM analysis a Pure culture of Streptomyces sp. isolate No. 5 grown on CGA 28°C ± 1 for 7 days b Scanning electron micrograph of Streptomyces sp. isolates No. 5 showing spore chains

Fig. 10

Molecular identification of Streptomyces sp. isolate No. 5 a Ladder b Amplification of 16S rDNA of Streptomyces sp. isolate No. 5 by PCR