In this PhD project, a microbial system for the production of the biodegradable polyester polyhydroxybutyrate (PHB) will be developed. An organism capable of direct PHB production from syngas has not been described yet. Thus the production of PHB requires an expansion of the metabolic capability of microorganisms via i) genetic engineering or, ii) co-cultivation of microorganisms. This study will focus on the development and exploitation of metabolic microbial networks using co-cultures (defined or open cultures). In the first phase of the project we will construct and test a defined co-culture of an acetogenic bacterium – converting CO (or syngas) to acetate – together with Rhodospirillum rubrum – using acetate and CO to accumulate PHB. A screening of several carboxydotrophic acetogens will be done for the selection of the most adequate acetogenic bacterium for this co-culture. This acetogen needs to be able to grow in the environmental conditions under which R. rubrum accumulates PHB, i.e. pH 7, 30°C and nitrogen-limited medium. Performance of acetogens under nitrogen-limitation has not been studied yet. The outcome of this screening of acetogens, mainly the effect on the acetate/ethanol ratio produced, will by itself be an interesting contribution to the knowledge on acetogens. Once an acetogen is selected the co-culture can be attempted and characterized. A second research line will focus on a bottom up approach, in which a PHB accumulating sludge will be tested for growth on syngas. If this is successful, the active organisms in this community will be characterized.
We provide a disciplinary and multidisciplinary research programme aimed at advanced understanding of environmental problems and advanced training of PhD candidates in this field.