Q.81 Which of the following antibiotics is/are isolated from Streptomyces spp.?
(A) Gentamicin
(B) Nystatin
(C) Polymyxins
(D) Tetracyclines

Gentamicin, Nystatin, and Tetracyclines are isolated from Streptomyces spp., while Polymyxins are not. The correct answer is (A), (B), and (D).

Option Analysis

Gentamicin (A)
Gentamicin, an aminoglycoside antibiotic, is produced by Micromonospora species like Micromonospora echinospora or Micromonospora purpurea, not Streptomyces. Its biosynthesis involves pathways distinct from typical Streptomyces-derived aminoglycosides like streptomycin.​

Nystatin (B)
Nystatin, a polyene macrolide antifungal, is biosynthesized by Streptomyces noursei. The complete gene cluster for its production, including polyketide synthase genes, has been identified in this species.​

Polymyxins (C)
Polymyxins (e.g., polymyxin B and colistin) are lipopeptide antibiotics produced by Paenibacillus polymyxa, a Gram-positive bacterium unrelated to Streptomyces.​

Tetracyclines (D)
Tetracyclines, including oxytetracycline and chlortetracycline, are produced by Streptomyces species such as Streptomyces rimosus and Streptomyces aureofaciens through polyketide pathways.​

Introduction
Antibiotics isolated from Streptomyces spp represent a cornerstone of modern medicine, powering treatments for bacterial and fungal infections. Streptomyces, soil-dwelling actinomycetes, produce over 80% of clinically used antibiotics, including key players like tetracyclines and nystatin. This article breaks down Gentamicin, Nystatin, Polymyxins, and Tetracyclines—their microbial origins, mechanisms, and relevance for CSIR NET Life Sciences aspirants searching for “antibiotics isolated from Streptomyces spp.”​

Streptomyces as Antibiotic Powerhouse

Streptomyces spp excel in secondary metabolite production via polyketide synthases and non-ribosomal peptide synthetases. Species like S. rimosus yield oxytetracycline, while S. noursei produces nystatin. These antibiotics target protein synthesis, cell walls, or membranes, revolutionizing infection control.​

Detailed Option Breakdown

• Gentamicin: Not from Streptomyces; sourced from Micromonospora echinospora. Inhibits bacterial protein synthesis but differs from Streptomyces aminoglycosides like streptomycin.​

• Nystatin: Isolated from Streptomyces noursei. Binds ergosterol in fungal membranes, causing leakage; vital for candidiasis treatment.​

• Polymyxins: Derived from Paenibacillus polymyxa. Disrupt Gram-negative outer membranes; last-resort for multidrug-resistant infections.​

• Tetracyclines: Produced by Streptomyces aureofaciens and S. rimosus. Block 30S ribosomal subunit, effective against broad-spectrum pathogens.​

CSIR NET Exam Insights

For competitive exams, memorize Streptomyces links: tetracyclines (S. rimosus), nystatin (S. noursei), but exclude gentamicin (Micromonospora) and polymyxins (Paenibacillus). Biosynthesis questions often test gene clusters and pathways.​