Metabolite production optimization

Here, it can be seen that during the last decade research on the design of plant cell bioreactors has witnessed a boom and reached maturity. A future trend in this area is to combine bioreactor type with operational conditions for specific cell lines of characteristic morphology, physiology and metabolism, in order to optimize the processes for secondary metabolite production. 

What can be done to achieve this necessary improvement Most plant cell products are secondary metabolites, which means that plant suspension culture systems involve a growth phase and a production phase. In any commercial system, one will probably want to separate physically these two phases. Unfortunately, one has to add a growth hormone such as 2-4-D for a successful growth phase, and these hormones must be completely removed before elicitors are added to the production phase to induce the secondary product. Optimizing this two-stage system is an engineering challenge. 

The pH of the media must be monitored and, in many cases, held constant. Temperatures must be carefully controlled during fermentation to maximize yields. The nature of the media, such as carbon and nitrogen sources, directly determines the quality of the odor released and the range of secondary metabolites produced. Optimization of the production of volatiles must also take into account the physiological state of the microorganisms. 

Yoder (13) makes the additional comment that "virulence may not always be correlated with the quantity of toxin produced in culture" even when the toxin is known to play a role in pathogenesis. It is important to note that the production of either primary or secondary metabolites in vitro is a complicated problem as will be discussed later. Research to optimize metabolite production in vitro has seldom been carried out for phytotoxins. This renders any positive correlation between in vitro toxin production and virulence of a strain purely fortuitous. A poor correlation may simply indicate that suboptimal conditions for the production of the putative phytotoxins were used. 

Better control over the physical environment and growth conditions for the cells composition, temperature, and pH of the growth medium to permit optimization of productivity and selectivity of metabolite production. 

In conclusion, for the optimization of secondary metabolites production by media design several considerations should be taken into account. In many cases it is necessary to develop a growth medium and a production one. In the first case, it is necessary to select a basal medium and optimize it for the maximal biomass production. 

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