Growth of hairy-root cultures in various bioreactors for the production of secondary metabolites.

Agrobacterium rhizogenes-mediated hairy-root cultures are a very promising alternative to the biotechnological exploitation of plant cell cultures. Their characteristic capacity for secondary-metabolite production, inherent genetic stability reflected in stable productivity and the possibility of genetic manipulation to increase biosynthetic capacity have initiated a considerable interest, both as a fundamental research tool and as a source of valuable products. One of the most important limitations for the commercial exploitation of hairy roots is the development of technologies for large-scale culture. Though these roots have been grown in various bioreactors--stirred-tank, bubble-column, airlift or submerged, trickle-bed and nutrient mist--the question as to which of these alternatives can be successfully and economically scaled-up has yet to be definitively answered. This present minireview highlights various perspectives of hairy-root cultures, describes a comparative scale-up study and discusses various aspects of these cultures when grown in various bioreactors for the production of secondary metabolites.