Synthetic and systems biology for cost-competitive γ-PGA production

Abstract

γ-PGA is a natural polymer secreted by Bacillus subtilis and other bacteria with huge potential in various biotechnological fields. Yet its commercial development is lagging behind due to the still high price. To increase the industrial attractiveness of this product it is therefore necessary to focus research efforts on reducing production costs. This objective can be achieved through different approaches which can be synergistically combined: 1. The expression of the pgs operon for biopolymer synthesis can be improved; 2. The bacterial metabolism can be modified a. so that cost-competitive substrates, such as industrial or crop waste products, can be used as feedstock; b. to accumulate the metabolic precursors required for product synthesis. Our aim is to act at all these levels with a common strategy, i.e. exploiting tools and data made available by synthetic & systems biology. For the first approach we are quantitatively evaluating the endogenous expression of the pgs operon, in order to tune it using pre-characterized regulatory "parts" from recently described libraries. For the second approach glycerol by-produced in biodiesel plants was chosen as low cost feedstock. We assessed the propensity of the γ-PGA producer and other B. subtilis strains to grow on glycerol analyzing its consumption flux compared to that of glucose, used until now. For optimization, the glycerol uptake and catabolic genes will be up-regulated with synthetic biology tools. Finally, a systems biology approach, exploiting genome-scale metabolic models, was chosen to identify genes whose deletion /over-expression should allow accumulation of the metabolic precursors necessary for γ-PGA production. The first results of such a multilevel strategy will be presented and discussed