Streptomycin: Structure, Mechanism of Action & Industrial Production by Fermentation Explained

Table of Contents

• Introduction to Streptomycin
• Chemical structure of Streptomycin
• Mechanism of Streptomycin Production
• Industrial production of Streptomycin by fermentation
• Harvest of Streptomycin
• References

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Introduction to Streptomycin

• Streptomycin was discovered in 1943 by Selman Waksman and Albert Schatz, marking a monumental moment in medical history as the first successful drug against Tuberculosis (TB), and it rapidly became a critical tool that transformed the treatment landscape for this devastating global epidemic.
• Streptomycin is biologically obtained from Streptomyces griseus, which belongs to the class Actinomycota, and appears as a thin, thread-like, filamentous, Gram-positive bacterium under the microscope, widely recognized for its prolific production of bioactive compounds, making it one of the most important microorganisms in natural product discovery.
• Streptomyces griseus and related species are primarily found in soil and decaying vegetation, where they play an essential ecological role in breaking down complex organic matter and recycling nutrients in the environment.
• Colonies of Streptomyces griseus are typically tough and leathery, often exhibiting a chalky, powdery, or dusty appearance due to the formation of spores on aerial hyphae, and they commonly produce grey spore masses.
• Along with other Streptomyces species, Streptomyces griseus is responsible for the characteristic “earthy” smell of healthy soil, which is due to the production of a volatile compound called Geosmin.
• Streptomyces griseus is known to produce over 30 different structural types of bioactive compounds in addition to streptomycin, including other antibiotics such as grisein and candicidin, as well as enzymes like pronase E.
• The production of these secondary metabolites, including antibiotics, provides Streptomyces griseus with a competitive advantage in nutrient-scarce, microbe-rich soil environments, enabling it to inhibit the growth of competing microorganisms and enhance its survival and ecological dominance.

Chemical structure of Streptomycin

• Streptomycin belongs to the aminoglycoside group of antibiotics, which are named for their characteristic structure consisting of amino sugars linked by glycosidic bonds, and these compounds are highly basic due to the presence of multiple amino groups, making them positively charged (polycations) within the body.
• The chemical structure of Streptomycin consists of three main components, among which streptidine acts as the aminocyclitol moiety that connects two sugar components, namely streptose and N-methyl-L-glucosamine.
• Streptidine is chemically defined as a 1,3-dideoxy-1,3-diguanidinoscyllo-inositol, and its ring structure is derived from inositol, which is a sugar-like cyclic alcohol, but its most important structural feature is the presence of two guanidino groups that are strongly basic in nature.
• The presence of these guanidino groups in streptidine is essential because they contribute significantly to the overall positive charge of Streptomycin and enable the drug to effectively bind to the bacterial ribosome, which is crucial for its antimicrobial action.
• Streptidine is linked to two amino sugars, streptose and N-methyl-L-glucosamine, through glycosidic bonds, and together these amino sugars are collectively referred to as streptobiosamine.
• Streptose is a unique branched-chain five-carbon sugar that exists in a furanose form, consisting of a five-membered ring with four carbon atoms and one oxygen atom, structurally resembling tetrahydrofuran.
• N-methyl-L-glucosamine, on the other hand, is derived from pyranose and exists in a more stable six-membered pyranose ring form, which contributes to the structural stability of the molecule.
• Streptose contains an aldehyde group, and when this group is reduced to an alcohol, it leads to the formation of Dihydrostreptomycin.
• Dihydrostreptomycin has been associated with more frequent and irreversible damage to the auditory portion of the inner ear, resulting in permanent deafness.
• In contrast, Streptomycin primarily affects the vestibular (balance) part of the inner ear rather than the auditory component.
• Due to its severe toxicity profile in humans, Dihydrostreptomycin is now mainly used in veterinary medicine for treating bacterial infections in livestock such as cattle, pigs, and sheep.

Mechanism of Streptomycin Production

• Streptomycin exerts its antibiotic activity primarily through its ability to bind irreversibly to the bacterial ribosome, a process that is strongly facilitated by the presence of multiple basic amino and guanidino groups within its structure, which become positively charged (polycations) at physiological pH.
• This overall positive charge is essential because it enables Streptomycin to be electrostatically attracted to the negatively charged bacterial cell surface, allowing the drug to be efficiently taken up into the bacterial cell.
• Once inside the cell, the multiple positive charges of Streptomycin promote strong binding to the negatively charged phosphate backbone of the 16S ribosomal RNA located within the 30S ribosomal subunit.
• The complete three-part molecular structure of Streptomycin, consisting of streptidine, streptose, and N-methyl-L-glucosamine, is essential as it fits precisely into the ribosomal binding pocket, ensuring stable and irreversible attachment.
• This binding results in two major lethal effects on the bacterial cell, as it blocks the initiation of new protein synthesis, thereby preventing the formation of functional protein chains required for survival.
• Additionally, Streptomycin causes misreading of the mRNA code during translation, leading to the production of abnormal, non-functional, or toxic proteins.
• Ultimately, although streptidine and its guanidino groups provide the crucial positive charge necessary for initial interaction, the integrity of the entire molecular structure is required to achieve a perfect fit on the 30S ribosomal subunit and produce the bactericidal (cell-killing) effect.

Industrial production of Streptomycin by fermentation

• The industrial production of Streptomycin is carried out in large, sterile bioreactors (fermenters) under carefully controlled environmental conditions through a process known as submerged fermentation.
• The production organism, Streptomyces griseus, is grown in a liquid culture medium (aqueous broth) that contains all essential nutrients required for microbial growth and antibiotic production.
• The fermentation process requires continuous supply of sterile air because Streptomyces griseus is strictly aerobic, and optimal temperature and pH must be maintained throughout the process for several days to ensure efficient production.
• The culture media used for the growth of Streptomyces griseus and production of Streptomycin consist of basic components such as carbon sources, nitrogen sources, and salts, which have been historically established and later modified depending on the microbial strain and industrial requirements.
• A classical medium described by Woodruff and McDaniel (1954) includes 1% soybean meal as a nitrogen source, 1% glucose as a carbon source, and 0.5% sodium chloride.
• Another formulation by Hockenhull (1963) includes 2.5% glucose as a carbon source, 4% extracted soybean meal as a nitrogen source, 0.5% distilleries dried solubles, 0.25% sodium chloride, and an initial pH adjusted to 7.3–7.5 before sterilization.
• The commercial fermentation process of Streptomycin is divided into three distinct phases based on growth characteristics and metabolite production.
• In the first phase, which lasts approximately 24 hours, rapid growth of Streptomyces griseus occurs with maximum mycelial biomass formation, ammonia is released into the medium due to proteolytic activity, carbon is utilized slowly, and only slight production of Streptomycin occurs, with pH ranging between 6.8 and 7.5.
• In the second phase, lasting from about 24 hours up to 6–7 days of incubation, there is rapid and increased production of Streptomycin, with no further mycelial growth indicating a stationary biomass, ammonia is utilized, glucose is progressively depleted from the medium, and pH remains relatively stable between 7.8 and 8.
• In the third phase, glucose becomes completely depleted, production of Streptomycin ceases, pH rises further, microbial cells undergo lysis, and ammonia is released back into the medium.

Harvest of Streptomycin

• After completion of fermentation, Streptomycin is separated from the culture broth and subjected to purification processes to obtain a clinically usable product.
• Streptomycin is a basic, positively charged compound (polycationic aminoglycoside), and this property is exploited during purification using ion-exchange chromatography, where resins specifically bind positively charged molecules.
• In ion-exchange chromatography, Streptomycin is captured by the negatively charged resin through electrostatic interactions.
• The bound Streptomycin is then eluted (released) from the resin by using appropriate acid or base solutions that disrupt these ionic interactions.
• After elution, Streptomycin is precipitated from the solution, commonly in the form of a stable streptomycin sulphate salt, which enhances its stability and suitability for storage.
• The purified product of Streptomycin is then dried and processed into final pharmaceutical formulations for clinical use.
• The overall efficiency, yield, and cost-effectiveness of Streptomycin production depend heavily on the optimization of both fermentation parameters and downstream purification techniques.

References

• RCSB Protein Data Bank. (2016). Streptomycin. In Global Health: Antimicrobial resistance. Retrieved from https://pdb101.rcsb.org/global-health/antimicrobial-resistance/drugs/antibiotics/protein-synthesis/ribosome/aminoglycosides/streptomycin/streptomycin
• Dimitrios Petrides, Ayman Mustafa, Rui Da Gama Ferreira, & Nikolaos Misailidis. (2022). Streptomycin production via fermentation: Process modeling and techno-economic assessment (TEA) using SuperPro Designer. ResearchGate.
• Author, A. A., Author, B. B., & Author, C. C. (Year). Optimization of a culture medium for streptomycin production using response-surface methodology. Journal Title, Volume(Issue).
• A method for the large-scale production of streptomycin by surface culture. Microbiology Society.
• Streptomycin mechanism of action and ribosome interaction. (n.d.). YouTube. https://www.youtube.com/watch?v=rVcMt4wLFQA
• Streptomycin production and industrial process. (n.d.). YouTube. https://www.youtube.com/watch?v=OQlC65DD3Ig
• Production of streptomycin: Definition, production & uses. Biology Reader. Retrieved from https://biologyreader.com/production-of-streptomycin.html