## 2 Environmental Cues and Co-Cultivation  
Stimulating Secondary Metabolite Production through Changing Culture Conditions: The \"OSMAC\" Approach  
Microbial physiology is influenced by cultivation environment, media and conditions [19]. It follows, therefore, that the production of secondary metabolites and bioactive compounds will be influenced by metabolic factors, themselves influenced by the prevailing environment. Broadly considered a form of strain improvement, manipulation of culture conditions has been used for decades as a mechanism of improving outputs from living organisms. Small changes in the composition of the growth media can induce not only variation in the amount of specific compounds, but also the production of a completely different pattern of molecules [20; 21; 22]. [PERSON] and co-workers coined the term \"OSMAC\" (one strain many compounds), which simply summarized the ability of single strains to produce different compounds when growing under different conditions [20]. While our understanding of the physiological and nutrient factors that pervade in the marine ecosystem is still partial at best, some clues have emerged to underpin early culture improvement studies. Screening of a panel of extracts from  
Figure 2: The integration of classical culture based and molecular biology based approaches for the elicitation of natural products from silent BGCs. A major challenge to the biodiscovery community, the cooperation of biological and chemical expertise is driving integrative technology developments that will unlock the silent potential of the cryptic gene clusters. Synthetic biology and combinatorial chemistry approaches further underpin the potential diversity of natural product that can be achieved. the marine fungus _Spicaria elegans_ grown under 10 different culture conditions revealed a dramatic shift in the profile of secondary metabolites produced [23]. This included the isolation of the novel spicochalasin A, five new aspochalasins M-Q, and two known aspochalasins. Subjecting the marine-derived fungus _Ascotricha_ sp. ZJ-M-5 to the OSMAC approach yielded three new caryophyllene derivatives and the known 1,3,6-trihydroxy-8-methylxanthone in Czapek Dox broth with or without Mg\({}^{2+}\)[24]. Examples from other ecosystems are provided by the detailed work of [PERSON] and co-workers, which repetitively showed how the phosphate concentration greatly influences the production of secondary metabolites in streptomycetes species [21]. They showed how cross-talk between global nutritional regulators has a great effect on both primary and secondary metabolites [25]. Similarly, also the carbon sources have been shown to greatly affect secondary metabolites production in a wide range of microorganisms [26]. Other easily accessible cultivation parameters can be modified, e.g., temperature, salinity, aeration, shape of the flasks, and these strategies led [PERSON] and colleagues [20] to show that _A. ochraceus_, known to synthesize only aspinonene, was able to produce 15 additional metabolites when grown under different cultivation conditions. Similarly, applying the OSMAC approach three new compounds belonging to the rare class of 22-membered macrolaton polyketides were isolated from the bacterium _Streptomyces_ sp. C34 [27]. The power of this approach was further reinforced by the work from [PERSON] and colleagues [28], who were able to characterize six new secondary metabolites produced by the plant-associated fungus _Paraphaeosphaeria quadriseptata,_ simply by changing the water used for the media preparation from tap water to distilled water. Although the exploration of bioactive compounds from the marine environment is gaining an increased interest in recent years [29], systematic studies aimed at testing the effect of different cultivation conditions on secondary metabolite production by microorganisms are scarce. Nevertheless, changing nutrient regimes, and media composition have been shown to influence secondary metabolites production also in marine microorganisms [30,31].