Microbes In Human Welfare

Step 1: Role of microorganisms in yoghurt production.
Yoghurt is produced through the fermentation of milk using specific bacteria. \textit{Streptococcus thermophilus} and \textit{Lactobacillus delbrueckii subsp. bulgaricus} are commonly used starter cultures.

Step 2: Explanation of other microorganisms.
Streptococcus penicillium (Option B):} Incorrect. This is not a known species used in yoghurt production.

Penicillium roqueforti (Option C):} Incorrect. This fungus is used in the production of blue cheese, not yoghurt.

Aspergillus niger (Option D):} Incorrect. This fungus is used for industrial production of citric acid, not yoghurt. \[ \therefore \text{The correct answer is: Streptococcus thermophilus

Concept:
Many important antibiotics used in medicine are produced by soil microorganisms, particularly bacteria belonging to the genus Streptomyces. These bacteria are well known for producing a wide range of secondary metabolites that act as antibiotics and help inhibit the growth of other microorganisms. Different species of Streptomyces produce different antibiotics, which have been widely used in the treatment of bacterial infections.
Step 1: Understanding the role of Streptomyces species.
Members of the genus Streptomyces are filamentous bacteria commonly found in soil. They play a major role in antibiotic production because they synthesize bioactive compounds that can suppress or kill pathogenic microbes.
Step 2: Important antibiotics produced by different species.

• Streptomyces erythreus → Produces Erythromycin, an antibiotic used to treat respiratory and skin infections.
• Streptomyces venezuelae → Produces Chloramphenicol, also known as Chloromycetin.
• Streptomyces griseus → Produces Streptomycin, the first antibiotic discovered for treating tuberculosis.
• Streptomyces aurifaciens → Produces Chlortetracycline, which is commercially known as Terramycin.

Step 3: Identifying the organism producing Terramycin.
Among the listed species, Streptomyces aurifaciens is the microorganism responsible for producing the antibiotic chlortetracycline. This antibiotic is marketed under the trade name Terramycin and is widely used as a broad-spectrum antibiotic.
Final Answer: