Secondary metabolites environmental factors

Like many traits, concentrations of secondary metabolites in algae are determined by a combination of genetic and environmental factors. Secondary metabolites are known to respond to changes in a variety of environmental conditions, including light,14,49,70 herbivory,43" 6, nutrients,44,45,49,73,74 desiccation,75 and salinity.76 Most of these studies have looked at the effects of a single environmental stress at once. However, in nature, multiple stresses often occur simultaneously and may have synergistic effects. 

It is estimated that there are in excess of 20 000 unique chemicals present as plant primary and secondary metabolites (Ohlrogge, 1994). The levels present in foods can vary quite considerably depending on the variety and on agronomic and environmental factors. To attribute benefits to any one chemical or group of chemicals seems a daunting task. Thus, in spite of intensive work in the last decade or so, there is still insufficient evidence with which to support the antioxidant hypothesis , or any other hypothesis, and to attribute... 

Plant cell culture is useful in laboratory and in industry because it allows plant natural products to be produced in a relatively controlled manner, and provides a supply of plant material that is not affected by sourcing problems, such as environmental, seasonal, geographical, and political factors.Also, plant cell culture allows for the tweaking and rearrangement of secondary metabolite biochemical pathways in order to produce novel metabolites, and to increase target compound yields, as well as allowing derivatives to be formed by introduction of analogs of natural intermediates.Plant cell culture can be performed with callus and suspension cultures, as well as with shoot cultures and hairy root cultures. These latter two approaches are especially useful when a metabolite is found to be produced more readily in differentiated cells. 

Secondary metabolites may also be found in animals, but 80% of all such metabolites known are of plant origin. An explanation for this wealth of plant-originated secondary metabolites may be the fact that plants are rooted and immobile. Hence they do not have the ability, vital to animals, to move away from danger. Plants do not respond to the environment in the same way as animals do. Nevertheless, they are exposed to weather conditions, soil factors, gradual environmental pollution, herbivorous animals or symbiotic organisms and other competing plants [3]. 

Environmental conditions may also affect chemical defense concentrations indirectly by changing the intensity of grazing, which can alter defense concentrations in algae with inducible defenses. Evidence for the direct effects of environmental factors on secondary metabolite concentrations are discussed below. 

So far, we have just scratched the surface of bacterial diversity, yet there are many unanswered questions which are intrinsically connected to the future success of natural product research. How many different microbes do exist What is the real extent of this diversity How does microbial diversity correlate to chemical diversity of the secondary metabolites produced What does all that microbial diversity do How do species evolve Are there environmental factors that support horizontal gene transfer Are there ecosystems and microhabitats that have higher probabilities to attract or support microbes with biologically attractive secondary metabolism ... 

The preceding sections have focused on the molecular aspects of evolution of enzyme efficiency, specificity, and regulation. Flowever, it is important to remember that enzymes evolve in a cellular context. Natural selection acts upon the fitness of the organism, which is a complicated function of properties such as growth rate, robustness to environmental perturbations, ability to construct a protective biofilm, resistance to toxins, or synthesis of secondary metabolites that impair competitors. The catalytic capabilities of enzymes, as well as the repertoire of enzymes maintained by individual species of microbes, have been shaped by these environmental factors over billions of years. 

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