Streptomyces are bacteria belonging to the Actinobacteria. They are used to produce antibiotics.
What are streptomyces?
Streptomyces are a genus of bacteria belonging to the order Actinomycetales and the family Streptomycetaceae. They belong to the gram-positive bacteria. This means that they can be stained blue in the Gram stain. In contrast to the Gram-negative bacteria, the Gram-positive bacteria do not have an additional outer cell membrane, but have only a thick peptidoglycan layer of murein. Streptomyces are aerobic bacteria. They therefore require oxygen for their energy production. In addition, they belong to the mycelium-forming bacteria. Like many representatives of the bacterial order Actinomycetales, they form filaments, the mycelia. These are elongated, branched cells, which form networks. The individual filaments have a diameter of 0.5 to 1 µm. Mycelia can be distinguished between two forms. The substrate mycelium grows in a nutrient medium. This can be liquid or solid. The air mycelium grows in the gas space above the nutrient medium. Spores can develop from the mycelia. However, these are endospores that bear no resemblance to the exospores formed by bacteria such as Clostridia or Bacillus.
Occurrence, distribution, and characteristics
The bacterial genus Streptomyces is found predominantly in soils. A large number of the bacteria produce odorants during energy production. Among them is geosmin. Geosmin smells earthy-musty and is perceived by many people as the typical soil odor of earth or forest soil. However, it is also responsible for the odor of mold. In addition, geosmin is involved in the odor that people perceive when rain starts after a long dry period. Thus, Streptomyces geosmin is responsible for a variety of familiar odors in nature. Streptomyces are aerobic bacteria that are found in their active form primarily in soils, but also in water. Compost, for example, contains particularly large numbers of streptomyces. Streptomyces are also present in the so-called rhizosphere of plants. The rhizosphere is the space in the soil that is directly affected by the root of a plant. Similarly, the bacteria are found in the digestive tract of worms or arthropods. In unfavorable environmental conditions, usually only inactive spores of Streptomyces are present. These spores can survive for a very long time even in poor conditions and serve to spread the bacteria. The bacteria thrive best at 25 to 30 °C. However, some bacteria in the genus Streptomyces are also thermophilic, preferring temperatures between 28 and 55 °C. Psychrophilic Streptomyces, on the other hand, like the cold. Optimally, bacteria grow at a pH between 6.5 and 8, so they are found preferentially in pH-neutral or slightly alkaline soils. Acidic soils are preferred by only a few bacteria from the Streptomyces group.
Importance and function
Many of the Streptomyces species are useful to humans. They are used as antibiotic producers. For example, Streptomyces aureofaciens produce tetracycline and chlortetracycline. Tetracycline is a broad-spectrum antibiotic used against various bacterial infections. One use of the antibiotic is acne. Chlortetracycline is used to treat bacterial infected wounds. The bacterium Streptomyces fradiae produces two antibiotics at once. Neomycin is a broad-spectrum antibiotic that is primarily effective against Gram-positive but also Gram-negative bacteria. It blocks the protein biosynthesis of various bacteria so that they can no longer multiply. Neomycin thus belongs to the group of bacteriostatic antibiotics. It is used in the form of a sulfate salt for local infections of the skin or mucous membrane, for wounds or burns. As a sterile solution, the drug is used to treat bladder and urinary tract infections in catheter carriers or after urological surgical procedures. The other antibiotic produced by Streptomyces fradiae is tylosin. Tylosin is also a bacteriostatic antibiotic. It does not kill the bacteria, but prevents them from multiplying. Actually, the antibiotic is approved only in veterinary medicine. However, its use in the treatment of Crohn’s disease, a chronic inflammatory bowel disease, is currently being tested.Tylosin appears to have a positive effect on the intestinal inflammations that frequently occur in Crohn’s disease. But not only drugs against bacteria are produced with the help of these bacteria. Antimycotics can also be produced with Streptomyces bacteria. For example, Streptomyces noursei produces the antifungal drug nystatin. Nystatin is used to treat fungal infections. For example, infections with Candida albicans or Aspergillus fumigatus are treated with nystatin.
Diseases and ailments
In plants, certain bacteria from the Streptomyces genus can cause potato scab. Some bacteria are also dangerous to animals. In humans, Streptomyces play only a minor role as a pathogen. Most bacteria of this species are not human pathogens. Streptomyces somaliensis and Streptomyces sudanensis are exceptions. These pathogens cause mycetoma. Mycetoma is also called fungal tumor. It is a chronic inflammatory process of the skin. The disease has a very slow course and is characterized by an increase in volume of the affected part of the body. The foot is frequently affected. Numerous nodules appear. In the center of the nodules there are fistula-like openings from which a fluid is secreted. In this fluid there are small granules. As the disease progresses, the inflammation also reaches deeper structures such as bones or meninges.
