Biological inducers as regulators of secondary metabolite biosynthesis in actinobacteria

Abstract

With the development of biotechnology, unconventional methods of cultivating producers alongside other microorganisms or inducers are attracting increasing attention. Cultivating actinobacteria with biological inducers can lead to increased concentration and/or activity of synthesised secondary metabolites, as well as to the production of practically valuable metabolites that are not characteristic of monocultures. Actinobacteria, bacteria, fungi, and yeasts are used as biological inducers, mainly in the form of living cells, although supernatants and inactivated cells are also employed. Among the possible mechanisms of induction, the most commonly highlighted are intercellular interactions between producers and inducers, as well as the effect of inducer signalling molecules on the biosynthesis of secondary metabolites; however, this aspect remains insufficiently studied and requires deeper molecular and physiological investigation. Actinobacteria are cultivated with inducers in the laboratory mainly in flasks on shakers, although some researchers also use laboratory bioreactors, indicating the potential for process scale-up. Different nutrient media are often applied for the preparation of microbial inocula and for biosynthesis, which requires further optimisation for scaling-up to the industrial level. Not all authors provide a detailed description of preparing inocula of actinobacteria and other microorganisms, which makes it difficult to determine whether the cultivation was indeed performed with an inducer and limits reproducibility of the results. Furthermore, not all studies investigate the biological activity of the secondary metabolites obtained, which requires further study, as the feasibility of their industrial production and their potential practical applications largely depend on this.