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#Streptomyces

2 public questions tagged with this topic.

Basic Applied Biology

Maximum antibiotic producers belong to genus:

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.

Ref: Berdy J Antibiotics 2005; Watson Molecular Biology of the Gene 7th ed. Actinomycete secondary metabolism; NIH actinobacteria review.

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Basic Applied Biology

Antibiotic production by Streptomyces occurs mainly during:

Streptomycetes exhibit biphasic growth kinetics clearly separating primary trophophase from secondary idiophase, a regulatory hallmark crucial for industrial antibiotic production. During logarithmic growth phase when carbon, nitrogen and especially phosphate are abundant, global regulators like DasR respond to N-acetylglucosamine, PhoP to phosphate, and GlnR to nitrogen repressing biosynthetic gene clusters encoding polyketide synthases PKS and non-ribosomal peptide synthetases NRPS to prioritize biomass accumulation, DNA replication and protein synthesis. As nutrients become limiting at onset of stationary phase, intracellular alarmones ppGpp produced by RelA triggers stringent response, gamma-butyrolactones synthesized by AfsA accumulate as quorum signals, and cluster-situated regulators such as ActII-ORF4 for actinorhodin, RedD for prodigiosin and StrR for streptomycin become derepressed. Acetyl-CoA and amino acid precursors redirect toward secondary metabolites conferring competitive advantage in soil niche competition. Industrially, fermentations are deliberately prolonged in stationary phase using fed-batch control to maximize idiolite accumulation without growth interference. Such differentiation regulated by global second messenger cyclic di-GMP, sigma factor SigB and pleiotropic regulators AdpA controlling both morphological aerial hyphae formation and chemical differentiation, illustrating tight coupling of development and antibiotic biosynthesis critical for high titer strain improvement programs.

Ref: Berdy J Antibiotics 2005 Streptomyces secondary metabolites; Alberts Molecular Biology of the Cell 6th ed. Ch secondary metabolism.

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