Microbial secondary metabolites

More than 20,000 bioactive, so-called microbial secondary metabolites are known today. In nature, they can play many different roles, such as antibiotics, toxins, ionophores, bioregulators, and in intra- and interspecific signaling. Their most versatile producers are differentiating filamentous fungi and actinomycetes, followed by other bacteria, such as Bacillus, Pseudomonas, myxobacteria, and cyanobacteria. From a biotechnological point of view, bioactive metabolites have been mainly studied as potential anti-infectives (antibacterials, antifungals, antivirals, and antiparasitics). Many of them, originally discovered for their antibiotic activity, were developed further to become leading anticancer drugs, immunosuppressive agents for organ transplantation, successful pharmaceuticals targeting metabolic and cardiovascular diseases, or products to be used in agriculture and animal husbandry. Due to the diversity and complexity of their structures and biosynthetic pathways, fermentation on industrial scale remains the preferred method for their production. The development of large-scale production processes, first for penicillin, and then for a large variety of antibacterials and other bioactive molecules, has stimulated the development of the fermentation industry and contributed to the evolution of modern biotechnology, including the application of recombinant DNA techniques for improving the performances of the producing strains.