The Antibiotic Discovery of Streptomyces

Since Alexander Fleming’s discovery of penicillin in 1928, researchers have shifted their focus to a group of bacteria known as Streptomyces spp. These bacteria have become the most important source of antibiotics today [1][2]. Streptomyces are an essential gram-positive genus, vital in producing numerous antibiotics globally. Remarkably, between 70 to 80% of natural-product antibiotics discovered trace their origins back to these microorganisms [5][7].

Characteristics of Streptomyces

Streptomyces thrive in diverse environments, from the depths of oceans to the highest peaks of mountains [2]. Lacking the ability to move independently, they spread by producing thread-like hyphae in search of nutrients. As they mature, these hyphae form chains of spores. When resources become scarce, Streptomyces produce aerial hyphae that branch off to generate spores that endure harsh conditions, spreading to new territories (Figure 1) [4][10].

Their ability to produce antibiotics is linked to the sporulation cycle. During this process, they generate bioactive secondary metabolites that grant a competitive advantage. Each Streptomyces species contains multiple biosynthetic gene clusters responsible for producing specialised metabolites, which in turn can be used for antibiotics. The bacteria turn these genes on and off depending on several factors, including growth stage [9]. For instance, Streptomyces venezuelae carries a biosynthetic gene cluster that, when activated, enables the bacterium to produce a helpful antibiotic called Chloramphenicol, which is a potent antibiotic used to treat eye and ear infections in humans [13].

Contributions of Streptomyces to Medicine

Streptomyces play a crucial role in human medicine, veterinary practice, and agriculture [2][9]. Research on these microbes has contributed towards the development of over fifty distinct antibiotics – including tetracyclines, aminoglycosides, chloramphenicol, rifamycin, and others. They also produce highly valuable pharmaceutical products such as anticancer, antiparasitic, and antiviral drugs, such as bleomycin (used to treat cancer) and boromycin (commonly used to treat patients with HIV) [11]. In addition, these bacteria produce various enzymes and enzyme inhibitors necessary for industrial applications, along with immunomodifiers for therapeutic use [9].

Environmental Significance

Besides their medicinal properties, Streptomyces are essential in environmental processes. They actively break down organic matter, improving soil fertility. Additionally, Streptomyces produce geosmin, a compound that gives soil its distinct earthy smell. This compound also contributes to the pleasant aroma accompanying rainfall after a long dry spell, commonly known as the “summer rain” smell [6].