Microorganisms from different habitats have a great potential to produce specialized metabolites in tiny and well-organized factories through the use of dedicated regions of their genomes dubbed “biosynthetic gene clusters”. It has been noticed that there’s a discrepancy between the number of biosynthetic gene clusters in a microorganism’s genome and the actual number of different metabolites that can be observed under laboratory conditions. In other words, under standard laboratory conditions, we do see a small fraction of the potential for bioactive metabolites that a microorganism can make. It is up to scientists, thanks to bioinformatic tools, to investigate what is hidden and to find a way to make these “cryptic metabolites” awake from their dormant status.
An empirical strategy, the OSMAC approach (one strain – many compounds), has proven useful for the discovery of cryptic metabolites: it consists in simple modulations of the culture conditions, such as media composition, temperature, osmolarity and pH, in order to stimulate specialized metabolite production. For example, a highly saline medium can lead to the production of otherwise cryptic brominated or chlorinated metabolites (Wei H, Lin Z, Li D, Gu Q, Zhu T. OSMAC approach in the research of microbial metabolites-a review). Another way to modulate gene expression is the co-cultivation of microorganisms, mimicking the crosstalk between organisms occupying the same environment (Solem C, Jensen PR. Modulation of gene expression made easy. Appl Environ Microbiol. 2002 May).
We can say that microorganisms have their own intriguing reasons for synthesizing some and not other bioactive molecules, and we are grasping to understand them. The work performed so far by scientists has allowed to lift just some of the fog surrounding specialized metabolite biosynthesis and, hopefully, we will eventually become able to read and observe far more molecules than today’s.