Secondary Metabolites Have Functions in Nature

It was once popular to think that secondary metabolites were merely laboratory artifacts but today there is no doubt that secondary metabolites are natural products. Over 40% of filamentous fungi and actinomycetes produce antibiotics when they are freshly isolated from nature. In a survey of 111 coprophilous fungal 

The widespread nature of secondary metabolite production and the preservation of their multigenic biosynthetic pathways in nature indicate that secondary metabolites serve survival functions in organisms that produce them. There are a multiplicity of such functions, some dependent on antibiotic activity and others independent of such activity. Indeed in the latter case, the molecule may possess antibiotic activity but may be employed by a producing microorganism for an entirely different purpose. Some useful reviews on secondary metabolism have appeared in recent years [23,47 -49]. Examples of marine secondary metabolites playing a role in marine ecology have been given by Jensen and Fenical [50]. 

The view that secondary metabolites act by improving the survival of the producer in competition with other living species has been expressed more and more in recent years [51,52]. Arguments are as follows  

Only organisms lacking an immune system are prolific producers of these compounds which act as an alternative defense mechanism. 

The compounds have sophisticated structures, mechanisms of action, and complex and energetically expensive pathways [53]. 

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