Browsing by Person "Arnold, Stefanie"

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Evaluation of bio-oil produced from fast pyrolysis of lignocellulosic biomass as carbon source for bacterial bioconversion
(2020) Arnold, Stefanie; Hausmann, Rudolf
Scarcity of fossil resources, climate change and growing world population demand the transition from a fossil-based economy towards a bioeconomy – a knowledge-based strategy which relies on the efficient and sustainable integration of bio-based resources into value-added process chains. As lignocellulosic biomass is an abundant renewable resource which does not directly compete with food and feed, its deployment in biorefineries is of special interest for a sustainable bioeconomy. Owing to its compact and complex structure, suitable conversion techniques need to be selected. Combinations of thermochemical and biochemical conversion technologies are considered to be a promising approach regarding a fast and efficient conversion of lignocellulosic biomass into value-added products. Bio-oil derived from fast pyrolysis of lignocellulosic biomass is a complex mixture and composed of water and a wide variety of organic components. Among these components pyrolytic sugars and small organic acids are particularly interesting as potential carbon sources for microbial processes. However, bio-oil also comprises many unidentified substances, as well as components which are known to display adverse effects on microbial growth. To evaluate the potential and challenges of bio-oil as an alternative and sustainable carbon source for bacterial bioconversion this thesis was divided into three parts (Figure 1). In Part I different pretreatment strategies were applied and evaluated regarding their effect on stability and detoxification of bio-oil fractions. For this purpose, the organic solvent tolerant bacterial strain Pseudomonas putida KT2440 was applied as a reference system and cultivated on different pretreated bio-oil fractions. It was shown that solid phase extraction is a suitable tool to obtain bio-oil fractions with significantly increased stability along with less inhibitory substances. Part II is focused on the evaluation of small organic acids mainly present in bio-oil with respect to their suitability as feedstock for bacterial growth. Four biotechnological production hosts Escherchia coli, Pseudomonas putida, Bacillus subtilis and Corynebacterium glutamicum were cultivated on different concentrations of acetate, mixtures of small organic acids, as well as pretreated bio-oil fractions as carbon source for their growth. Results reveal that P. putida, as well as C. glutamicum metabolizes acetate – the major small organic acid generated during fast pyrolysis of lignocellulosic biomass – as sole carbon source over a wide concentration range and grow on mixtures of small organic acids present in bio-oil. Moreover, both strains show a distinct potential to tolerate inhibitory substances within bio-oil. Part III describes the growth behavior of a genetically engineered, nonpathogenic bacterium Pseudomonas putida KT2440 and its simultaneous heterologous production of rhamnolipid biosurfactants on bio-oil derived small organic acids and pretreated fractions. Results suggest that both maximum achievable productivities and substrate-to-biomass yields are in a comparable range for glucose, acetate, as well as the mixture of acetate, formate and propionate. Similar yields were obtained for a pretreated bio-oil fraction, although with significantly lower titers. In conclusion, this thesis shows that microbial valorization of bio-oil is a challenging task due to its highly complex and variable composition, as well as its adverse effects on microbial growth and issues with analytical procedures. This work depicts a proof of concept by outlining a potential biorefinery route for microbial valorization of pretreated bio-oil and its unexploited side streams. It provides a step in search of suitable bacterial strains for bioconversion of lignocellulosicbased feedstocks into value-added products and thus contributes to establishing bioprocesses within a future bioeconomy.