Investigations on poly([R]-3-hydroxybutyrate) (PHB) biosynthesis from syngas by Rhodospirillum rubrum, using a tailor-made syngas fermentation platform

In the third part of the thesis, the growth and PHB productivity by R. rubrum on syngas was characterized and optimized.Therefore, cultivations under dierent nutritional conditions using batch, fed-batch (Chapter 5) and chemostat (Chapter 6) techniques were used.The comparison of the performance of R. rubrum in dierent nutrient limited fed-batches (carbon [C], carbon-nitrogen [C,N], and carbon-phosphorous [C,P]) revealed that a C,P limitation had a positive inuence on PHB accumulation, whereas C,N limitation even stopped PHB accumulation of R. rubrum completely.The specic PHB productivity under C,P limitation was 5 times higher than during only C-limited growth.The highest PHB accumulation of 30 % w/w was reached at the end of the C,P-limited fed-batch.These fed-batch cultivations also revealed that the growth of R. rubrum was limited in all cases by the availability of energy from CO at 0.2 g CO g -1 dry biomass h -1 .Chemostat cultivations on syngas conrmed that the availability of CO limited growth of R. rubrum (gas-liquid transfer).However, the biomass concentration and PHB production could be increased by adding acetate as co-substrate.Feeding with dierent ratios of acetate:CO revealed that the PHB content correlated positively with the acetate:CO ratio.Furthermore, with an increasing acetate:CO ratio, the function of CO changed from being used as a carbon source to being used as an energy source .In summary, this thesis will set a new standard for safe lab-scale syngas fermentation and the collection of data during the biotechnological production of PHB from syngas.Furthermore, the systematic analysis of PHB production under dierent growth conditions serves as a basis for further process optimization to reach higher PHB production rates on syngas to go towards a more economic PHB biosynthesis.