PhD defense by Kim Olsson

Title of thesis: Engineering glycosyltransferases for the production of next generation stevia sweeteners

By Kim Olsson, ErhvervsPhD at Evolva A/S

Supervisors:
Prof. Birger Lindberg Møller, PLEN
Michael Dalgaard Mikkelsen, Evolva A/S

Summary
Stevia sweeteners are natural, high-intensity sweeteners from the Stevia rebaudiana Bertoni plant. They consist of the diterpenoid steviol backbone, glycosylated up to six times by four UDP-dependent glycosyltransferases (UGTs). UGTs are regiospecific rather than substrate specific resulting in a number of bottlenecks and side-products. This results in a low accumulation in the plant of the so called ”next generation stevia sweeteners”, rebaudioside D (Reb D) and rebaudioside M (Reb M), while the plant accumulates up to 14% of leaf dry weight in the precursors stevioside and rebaudioside A. These are also high-intensity sweeteners, but have an undesired lingering bitterness taste that is less present in Reb D and Reb M. In order to make the steviol glycosylation pathway more efficient towards the production of the next generation stevia sweeteners, it is necessary to optimize the Stevia UGTs to remove bottlenecks and to make them more substrate specific in order to avoid side-product formation. In the present work, three of the Stevia UGTs are optimized for catalytic efficiency and substrate specificity simultaneously through the use of site saturation mutagenesis screens based on different screening platforms.

Opponents:
Thomas Vogt, Leibniz
Michael Skjøt, Novo Nordisk
Chair: Søren Bak, PLEN

Everybody is welcome!