Extracellular synthesis of silver nanoparticles using entomopathogenic fungus: characterization and antibacterial potential

Research Article Extracellular synthesis of silver nanoparticles using entomopathogenic fungus: characterization and antibacterial potential Shruti Tyagi1 · Pankaj Kumar Tyagi2 · Deepak Gola2 · Nitin Chauhan3 · Randhir K. Bharti4 Received: 24 September 2019 / Accepted: 29 October 2019 / Published online: 5 November 2019 © Springer Nature Switzerland AG 2019 Abstract Present study involves the simple, rapid, non-toxic and in vitro method of extracellular silver nanoparticles synthesis using Entomopathogenic fungus (Beauveria bassiana). The development of silver nanoparticle in fungal supernatant was confirmed by the absorbance peak at 450 nm in UV–Vis spectrophotometer. Further, presence of AgNPs and its crystal lattice was confirmed by EDS and XRD, respectively. TEM micrograph confirmed the presence of differently shaped (triangular, circular, hexagonal) nanoparticles with size ranging from 10 to 50 nm. Variable shape and size of fungal assisted AgNps was also confirmed in SEM study. The optimal pH and temperature for biosynthesis of nanoparticles was found to be 6.0 and 25 °C, respectively. The continuous effects of AgNPs against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus in time dependent manner was confirmed in growth kinetic studies. During 36 h of growth study, maximum reduction in O.D560 was found in E. coli (67.2%) followed by P. aeruginosa (63.3%) and S. aureus (56.8%) at 30 °C. The MIC values of fungal assisted AgNPs against E. coli, P. aeruginosa and S. aureus was found to be 2.5, 3 and 4.5 ppm, respectively. The MIC values of Ciprofloxacin was observed to be 0.5, 0.5 and 0.7 ppm, whereas MICs of AgNPs + Ciprofloxacin showed 0.4, 0.4, 0.5 ppm against E. coli, P. aeruginosa and S. aureus, respectively, clearly highlighting the synergistic effect of AgNPs in combination with Ciprofloxacin. In the view of challenges for developing antimicrobial nanoparticles of variable shape and size by various other methods, tuning nanoparticles synthesis via fungi can be a wonderful approach to resolve existing hurdles. Keywords Silver nanoparticles · Entomopathogenic fungi · Antimicrobial · Antibiotic 1 Introduction The term “nano” is derived from a Greek word which means “dwarf ” [1, 2]. Synthesis of nanoparticles has gained attention due to their applications in multiple fields such as antifungal agents, antibacterial agents, biosensor, bioremediation, anticancer, drug delivery, etc. [3–10]. In addition to this, unique properties of nanoparticles such as size, shape, surface to volume ratio, high catalytic activity, etc. make them a unique candidate for multiple applications described above. The synthesis of nanoparticles via biological means has proved to be the better mode as compared to chemical and physical methods [1]. Chemical methods involve toxic chemicals and may generate hazardous or toxic by-product during synthesis, while physical methods have low efficiency and involves high consumption of energy to maintain optimal pressure and temperature during the synthesis * Deepak Gola, | 1Meerut Institute of Engineering and Technology, Meerut, Uttar Pradesh, India. 2Noida Institute of Engineering and Technology, Greater Noida, Uttar Pradesh, India. 3Department of Microbiology, Shaheed Rajguru College of Applied Sciences for Women, University of Delhi, New Delhi, Delhi, India. 4University School of Environmental Management, Guru Gobind Singh Indraprastha University, Dwarka, Delhi, India. SN Applied Sciences (2019) 1:1545 | https://doi.org/10.1007/s42452-019-1593-y Vol.:(0123456789) Research Article SN Applied Sciences (2019) 1:1545 | https://doi.org/10.1007/s42452-019-1593-y process [11, 12]. On the other hand, biological methods for the synthesis of silver nanoparticles provides many advantages i.e., environmental friendly, non-toxic and easy to scale up for large-scale synthesis [13–15]. Researcher across the world utilized biological entities such as plant (leafs, flower, seeds), bacteria, algae and fungi for the production of different type of metallic nanoparticles such as gold, silver, cadmium, iron, etc. and studied their applications in the field of medical, bioremediation, drug delivery etc. [16–19]. Among other metal nanoparticles, synthesis of silver nanoparticles (AgNPs) via biological mean gain wide acceleration due to their profound applications in medical application, textile dye removal, wastewater treatment, biological sensors etc. [16, 20–22]. Synthesis of AgNPs via fungi gain more attention because they produce large amount of biomass in a short period of time under lab conditions and produce large amount of extracellular protein that help in synthesis of nanoparticles [23, 24]. Dhanaraj et al. [17] observed the AgNPs synthesis potential of fungi Aspergillus niger and observed significant anti-bacterial properties of AgNPs against Staphylococcus aureus, Klebsiella pneumonia, Escherichia coli, and Salmonella typhi. In another study, Verma et al. [25] investigated the antimicrobial potential of AgNPs synthesized through Aspergillu sclavatus against Candida albicans, Pseudomonas fluorescens and Escherichia coli. Results clearly indicated anti-microbial activity with average minimum inhibitory concentration of 5.83 µg mL−1 against above microbial pathogens. However, the literature discussing about synthesis of AgNPs using entomopathogenic fungus and antimicrobial potential of synthesized nanoparticles is lacking [26, 27]. Most of the studies investigates larvicidal and insecticidal properties of these fungi [28]. Synthesis of AgNPs using entomopathogenic fungus provides additional advantages as they are non-pathogenic and insecticidal in nature. Earlier reports have highlighted the insecticidal potential of B. basssiana (entomopathogenic fungi) AgNPs. As per our findings, only one report has studied the antimicrobial efficacy of B. bassiana AgNPs against Staphylococcus aureus and Escherichia coli using well diffusion assay [29]. The present study investigated the extracellular AgNPs synthesis using Beauveria bassiana (entomopathogenic fungus) along with their antimicrobial potential. The antimicrobial activity of silver nanoparticles was compared with the antibiotic and AgNPs-antibiotic combination. The present report is the first investigation on the kinetic study of B. bassiana synthesized AgNPs against gram positive and negative bacteria at different time intervals with additional studies on AgNPs and antibiotic combination. Further, AgNPs were characterised via Transmission electron microscopy (TEM) equipped Energy dispersive Vol:.(1234567890) spectrometer (EDS), Scanning electron microscopy (SEM), X-ray diffraction (XRD) and zeta potential. 2 Materials and methods 2.1 Micro‑organisms and growth conditions In the present work, Beauveria bassiana was obtained from Institute of Microbial Technology (Chandigarh, India). The strain was stored at 4 °C on potato dextrose agar slant. Prior to experiments, culture was re (...truncated)