Strategies for Bioproduct Optimization in Plant Cell Tissue Cultures

Abstract

Cell cultures that can produce multiple products of commercial interest simultaneously have the potential to overcome economic barriers to commercialization. This paper reviews several strategies (elicitation, immobilization, medium optimization, differentiation, metabolic engineering, bioreactor considerations) for enhancing valuable product synthesis in plant cell cultures, with a focus on the production of Taxol from Taxus cell cultures (our laboratory research focus). While plants are capable of synthesizing valuable products (secondary metabolites), often undifferentiated tissue cultures cannot produce significant amounts of the target compound without the use of enhancement strategies. For example, cell immobilization cannot only protect cells from shear, but also promote secondary metabolism, in part due to increased cell interactions. The cell culture medium can be easily manipulated by changing sugar composition, type, and concentration of plant growth hormones, and the levels of phosphate and nitrogen. A two-stage process that promotes growth in the first stage and production in the second stage is often employed. Elicitation of enzyme systems can be used to achieve high levels of production. Methyl jasmonate is a signal transducer that has been shown to influence numerous plant species, including Taxus. Often, the synergistic application of these enhancement strategies is necessary to achieve acceptable product yields. There are also several issues to consider when designing a reactor for secondary metabolite production: shear stress, gas phase composition, and oxygen delivery. The generic strategies used to enhance secondary metabolite production in plant cell cultures can also be applied to increase hydrogen and valuable product yields in bacterial and algal systems.