Practice question

Genus Streptomyces, order Actinomycetales comprising filamentous Gram-positive bacteria with high GC content around 72 percent, represents most prolific source of bioactive natural products, accounting for more than two-thirds of clinically relevant antibiotics including streptomycin discovered by Waksman 1943, tetracycline, erythromycin, chloramphenicol, rifamycin and avermectin precursor of ivermectin. Large linear chromosome 8 to 10 Mb encodes 20 to 40 cryptic biosynthetic gene clusters per strain encompassing type I modular and type II iterative polyketide synthases, non-ribosomal peptide synthetases, lanthipeptide and terpenoid machinery. Complex morphological developmental cycle forming substrate mycelium penetrating soil and aerial hyphae differentiating into spores correlates temporally with activation of secondary metabolism through signaling molecules gamma-butyrolactones and methylenomycin furans acting on TetR family repressors. Ecological advantage in fierce soil competition drives chemical diversification mediated by horizontal transfer. Modern genome mining using antiSMASH platform continues to reveal novel antibiotics, sustaining dominance over Bacillus, Penicillium and Escherichia coli in discovery pipelines.