Marine Functional Metabolites
Contents
Introduction
Functional metabolites are biological molecules that have key physiological and behavioural functions that ensure the fitness and survival of an organism but that are not involved in primary metabolism such as proteins and nucleic acids that make up the basic machinery of life. The term functional metabolite is new and used as an alternative to the more often-used term “secondary metabolite” that considers these compounds as causing long-term impairment but not immediate death of an organism, or as causing no effect at all. The difference with our definition is that these compounds are not secondary but always serve a function that is necessary for the well-being and survival of an organism. The term functional metabolite differs from “natural product” which generally intends compounds with biomedical potential leading to drug discovery, but is rarely used in the ecological context. Other often-used terms with a more ecological context are “infochemicals” or “semiochemicals” that are defined as compounds that convey information between individuals thereby evoking a physiological or behavioral response in the receiver.
Whatever term used, metabolites of this nature generally represent only a tiny fraction of the total biomass of an organism compared to primary metabolites, and it is not always clear what the function of these compounds is and what advantages they offer to the producing organism. To date, more than 18,000 of these metabolites have been described from sponges, ascidians, soft corals, seaweeds, marine microbes and many other benthic and pelagic organisms, with more being discovered daily. Many of these compounds play fundamental roles as defences against predators, competitors and pathogens, and for the selection of mates and habitats. Without these compounds many key physiological processes would cease to exist, with catastrophic consequences on ecosystem functionality. For further details see:
Ecology of functional metabolites
There are many theories as to why marine organisms produce compounds that are not involved in primary metabolism. Early theories suggested that these were chemical waste products or otherwise functionless metabolites of primary metabolism overflow and this is probably why the term secondary metabolites was coined since these compounds were not considered important for the producing organism. However such compounds are now considered of vital importance and a whole new discipline named chemical ecology is now devoted to the study of the biological and ecological function of these compounds. Since marine organisms are under intense competitive pressure for space, light, and nutrients, they have developed numerous and complex chemical defenses to ensure survival. Some examples of the types of chemical interactions that have been best studied so far can be found in the following sections:
Biotechnological potential of functional metabolites
Most people are familiar with functional metabolites whether they know it or not. These are the compounds that give many of our foods wonderful aromas and tastes and many of our household cleaning agents their fresh scents. But these are just some of the obvious ways we have taken advantage of these compounds. Natural products (NPs) have extensively represented a source of biologically active molecules for the treatment of many diseases in their natural form or as a template for synthetic modification.
Nowadays it is estimated that approximately 61% of the 877 small-molecule new chemical entities introduced as drugs worldwide during 1981-2002 can be traced to or were inspired by natural products. The more convenient sources of drug leads include natural products (6%), natural products derived (27%), synthetic compounds with natural product-derived pharmacophores (5%) and synthetic compounds designed on the basis of knowledge gained from natural products (natural product mimics, 23%).
Within NPs, those derived by marine organisms (referred to as marine natural products, MNPs) represent a very promising and relatively unexplored family. The biodiversity of the marine environment far exceeds that of its terrestrial counterpart so the oceans represent an enormous resource for new biologically active compounds (biodiversity = chemical diversity). In a recent NCI study, marine animals were 10x more likely to contain selective cytotoxicity activity than terrestrial plants, animals or microorganisms.
Further reading
For further reading please consult the MarBEF ROSEMEB webpage with the reference list of relevant publications in chemical ecology at: http://www.marbef.org/projects/rosemeb/results.php
References
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