## 1 Introduction  
Physical and chemical techniques for the synthesis of nanoparticles involve complex protocols, high temperature requirements and the employment of hazardous compounds such as reducing agents, which not only leads to expensive costs but also the formation of toxic pollutants on the surfaces of the nanoparticles synthesized. The aspects mentioned not only cause uncertainty in the preparation steps but also directly question their applicability in biological systems. On the contrary, the synthesis of nanoparticles via green technology, also known as biological synthesis, makes use of biological organisms that are cost-effective, omits use of toxic chemicals and rather utilizes an eco-friendly approach of synthesis that has gained precedence over conventional physical and chemical techniques. Nanoparticle synthesis carried out by bacteria has gained interest due to their advantageous properties which include high growth rate, ease of cultivation and ability to grow in unfavourable environmental parameters (e.g., temperature, pH and pressure) [1]. The difference between bacteria and other green synthetic strategies such as plants is that bacteria can be genetically moulded and manipulated with ease for the biomineralization of metal ions. On the contrary, the use of plants for the synthesis of nanoparticles is not feasible as it is difficult to control growth parameters due to climate and environmental factors, and to regulate plant growth conditions sophisticated facilities, e.g., greenhouses are required which are not cost-effective as they require a lot of equipment and maintenance. Plants also require a long growth period before any part of the plant can be harvested for use whereas bacteria have a much quicker cultivation period and thus are of particular interest. Magnetotactic bacteria (MTB) can be described as aquatic prokaryotes whose movement is directed by the Earth's externally applied magnetic and geomagnetic fields due to their ability to exhibit magnetotactic behaviour known as'magnetotaxis'. These bacteria represent a morphologically, phylogenetically and physiologically diverse group of Gram-negative bacteria known to biomineralize unique organelles referred to as'magnetosomes' [2; 3]. Magnetosomes contain nano-sized particles composed of either magnetite (Fe\({}_{3}\)O\({}_{4}\)) or greigite (Fe\({}_{3}\)S\({}_{4}\)) depending on the species used, and these iron-containing particles are encased in a lipid bilayer membrane referred to as the magnetosomal membrane [3; 4; 5]. MTB-produced nanoparticles have garnered a lot of interest as these nanoparticles have a number of desirable properties that are not often present in physically and chemically synthesized nanoparticles, such as narrow size distribution, uniform morphology, a large single magnetic domain, and high levels of purity and stability [6; 7]. MTB-produced nanoparticles also have the added advantage of being easily dispersible and having facile functionalization due to their magnetosomal membrane [8]. The surface properties of magnetosomes allow significant amounts of specific molecules to be anchored on to the membrane which enables easy functionalization for various applications dealing with cell specific targeting [9]. Interestingly, these nanoparticles have been investigated as biotechnological tools in various applications which include but are not limited to drug delivery, cell separation, food safety, magnetic resonance imaging (MRI) contrast agents, antimicrobial agents and antioxidant agents, as well as other applications such as recovery or detection of DNA or antigens, hyperthermia treatment, enzyme immobilization and environmental applications focusing on wastewater treatment [10]. Synthesizing magnetosomes on a large scale for commercial applications is still quite challenging. The necessity for high magnetosome yield at affordable expenditure and energy cost is the main impediment to industrial-scale mass production of magnetosomes.