Abstract

Secondary metabolites are low molecular mass products of secondary metabolism which are usually produced by microorganisms experiencing stringent conditions. These metabolites are not essential for growth but serve diverse survival functions in nature. Besides offering survival advance to the producing organisms, they have several medicinal uses such as antibiotics, chemotherapeutic drugs, immune suppressants, and other medicines which benefited human society immensely for more than a century. This chapter provides an overview of various functions these secondary metabolites offer in nature from single-cell organisms to multicellular organisms. Furthermore, this chapter also discusses the underlying mechanisms behind their diverse functions and how these are regulated and synthesized under non-viable environmental conditions.

Highlights

  • Secondary metabolites are biologically active small molecules that are not required for growth and development but which provide a competitive advantage to the producing organism [1]

  • The bacterial secondary metabolites are a source of many antibiotics, chemotherapeutic drugs, immune suppressants, and other medicines

  • Secondary metabolites that upregulate the expression of oxidative stress responses can prime bacterial cells for tolerance and/or resistance to antibiotics, which is similar to the protective effects of exposure to sublethal concentrations of oxidants such as H2O2 [52]

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Summary

Introduction

Secondary metabolites are biologically active small molecules that are not required for growth and development but which provide a competitive advantage to the producing organism [1]. These are small organic molecules that consist of unusual chemical structures which include β-lactam rings, cyclic peptides, depsipeptides containing unnatural and non-protein amino acids, unusual sugars and nucleosides, unsaturated bonds of polyacetylenes and polyenes, covalently bound chlorine and bromine; nitro-, hydroxamic acids, and so on. Their enormous diversity includes 22,000 terpenoids as well [2]. The last section discusses how these secondary metabolites as antibiotics are regulated and synthesized with a special focus on Streptomyces as they are a rich source of natural antibiotics due to their prolific secondary metabolism

Secondary metabolites in nature
Agents of chemical warfare in nature
Metal transport agents
Induction of efflux systems
Modulation of oxidative stress
Upregulation of defenses against oxidative stress
Detoxification of ROS
Synergistic interactions between secondary metabolites and antibiotics
Interspecies antibiotic resilience
The regulation of the secondary metabolism of Streptomyces
Cluster-situated regulators (CSRs)
The stringent response and nutrient deprivation
Regulation of secondary metabolism by carbon
Regulation of secondary metabolism by nitrogen
Upsetting of zinc and iron homeostasis
Extracellular signaling molecules
Findings
Conclusions
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