99 © Springer Nature Singapore Pte Ltd. 2020 A. K. Shukla (ed.), Nanoparticles in Medicine, https://doi.org/10.1007/978-981-13-8954-2_4 A. Anandaradje · V. Meyappan · I. Kumar · N. Sakthivel (*) Department of Biotechnology, School of Life Sciences, Pondicherry University, Puducherry, India 4 Microbial Synthesis of Silver Nanoparticles and Their Biological Potential Annuja Anandaradje, Vadivel Meyappan, Indramani Kumar, and Natarajan Sakthivel 4.1 Introduction The word ‘silver’ was originated from the Anglo-saxon word ‘siosulfur’ and the symbol ‘Ag’ was derived from the Latin word ‘argentum’. Silver ions and silver salts have been exploited for therapeutic purposes since the rise of human civiliza- tion (Singh et al. 2017). Silver the lustrous transition metal exhibits good electrical and thermal conductivity and therefore be considered as premier metal for therapeu- tic applications. It is reported also that silver is more advantageous than risk factors (Firdhouse and Lalitha 2015). Silver nanoparticles (AgNPs) are a class of zero- dimensional materials that show innate morphology with the size ranging from 1 to 100 nm (Syafuddin et al. 2017). Among metal nanomaterials, AgNPs possess thera- peutic and clinical properties. AgNPs exhibit unique thermal conductivity, Raman scattering and chemical stability (Krutyakov et al. 2008; Tran and Le 2013). AgNPs have been synthesized by different approaches including physical, chemical and biological methods. Among synthesis methods, biological synthesis method using microbes is much preferred due to their cost-effectivity and reduced exposure to hazardous chemicals. However, microbial-mediated method also has potential drawbacks in the downstream processing during the separation of nanoparticles from the microbial materials used (Schröfel et al. 2014). Copious bacteria, yeasts, fungi and actinomycetes are exploited for the synthesis of AgNPs both intra- and extracellularly (Narayanan and Sakthivel 2010). AgNPs have been synthesized from cell-free extract and bacteria-derived components such as biosurfactants, acti- norhodin pigment and polysaccharides (Gupta et al. 1998; Klaus et al. 1999; Oves et al. 2013; Saifuddin et al. 2009; Satpute et al. 2010; Singh et al. 2013a). Due to increase in morbidity and mortality by common bacterial and viral diseases, antimi- crobial resistance has become a major threat. Hence, there is an urgent need to fght