Browsing by Subject "Biotechnology"

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Biotechnological conversion of lignocellulose hydrolyzates : model microorganisms for a bio-based economy
(2020) Horlamus, Felix; Hausmann, Rudolf
Lignocellulose has substantial potential as a carbon source in a bio-based economy. It is the most abundant renewable raw material on earth and is available in large quantities as waste from the agriculture, food and wood industry. It is composed mainly of the polymers lignin, cellulose and hemicellulose. In contrast to glucose derived from cellulose, hemicellulose sugars often remain unused although 60 billion tons of hemicelluloses are produced annually. Hemicelluloses are a group of heterogeneous polysaccharides consisting of different monomers such as D xylose, D arabinose, D mannose and D galactose. Lignocellulose is mostly depolymerized in order to obtain fermentable sugars. During the depolymerization process, inhibitors such as organic acids or furan aldehydes can be formed or released, which could be problematical for biotechnological processes. The aim of this thesis was to develop and evaluate bacterial-based biotechnological processes capable of using hemicellulose sugars as a source of carbon. First, Pseudomonas putida KT2440 was chosen. Pseudomonades are claimed as a promising chassis in biotechnology due to their versatile and robust metabolism. Unlike other Pseudomonades, the strain KT2440 is classified as biosafety level 1 in the American Type Culture Collection (ATCC). However, these bacteria can metabolize glucose as the only lignocellulose monosaccharide. Cellvibrio japonicus was the second selected bacterium. This strain is not yet established as a microbial host in biotechnology, but can degrade a huge portfolio of plant cell wall polysaccharides and is also classified as biosafety level 1 in ATCC. The topic of the first publication was to engineer P. putida KT2440 strains for metabolizing the hemicellulose monosaccharides xylose and arabinose and characterize their growth behavior. Initially, an arabinose metabolizing strain with the araBAD operon and a xylose metabolizing strain with xylAB operon was constructed. Later on, these strains were cultivated in minimal salt medium with glucose, xylose and arabinose as carbon sources in Erlenmeyer flasks. The recombinant P. putida KT2440 strains metabolized xylose and arabinose with high growth rates comparable to glucose. It turned out that both engineered strains were able to grow on both pentoses as well as on mixtures of glucose xylose and arabinose. The intent of the second publication was to evaluate P. putida KT2440 as a platform model organism for bioconversion of lignocellulose hydrolyzates. Strains were cultivated in minimal salt medium with several hydrolyzates as carbon source in Erlenmeyer flask and bioreactor. In addition, the growth-inhibiting effect of major toxic substances contained in lignocellulose hydrolyzates on P. putida KT2440 was analyzed via cultivation experiments. Several suitable hydrolyzates were figured out for this strain. Formic acid and acetic acid proved to be relatively unproblematic under pH neutral conditions, whereas furfural and hydroxymethylfurfural (HMF) had a negative effect on the bacterial growth. A diauxic-like growth behavior was revealed via fed batch bioreactor cultivations, since pentoses were almost not consumed with sufficient glucose supply. Consequently, feed-medium was added step-by-step in the next experiment. The applied feed profile did lead to an almost complete metabolization of xylose. The purpose of the third publication was to evaluate C. japonicus as a potential host strain for the one‐step bioconversion of xylans into rhamnolipids. Cultivation experiments were performed in Erlenmeyer flasks filled with minimal salt medium and containing different carbon sources. Furthermore, the strain was transformed with the plasmid pSynPro8oT carrying rhlA (encodes acetyltransferase) and rhlB (encodes rhamnosyltransferase I) to complete the rhamnolipid metabolism. The strain grew on all main lignocellulose monosaccharides as well as, on different xylans. Mono rhamnolipids were produced with the engineered strain using xylans as carbon source. This is particularly interesting as most industrially relevant bacteria are not able to depolymerize wood polymers. As the product yields were quite low, there are still many challenges in order to achieve an economically efficient process. Nevertheless, to the best of our knowledge, it is the first published one step bioconversion of hemicellulose polymers into rhamnolipids. In total, P. putida KT2440 turned out as a flexible and powerful model organism and two xylose and arabinose metabolizing strains were constructed. Moreover, bioreactor cultivations with lignocellulose hydrolyzates were performed and a feeding strategy to overcome diauxic-like growth behavior was presented. A proof of concept for a one-step bioconversion of xylans into rhamnolipids with a recombinant C. japonicus strain was successfully demonstrated.
Dietary phosphorus and calcium in feed affects miRNA profiles and their mRNA targets in jejunum of two strains of laying hens
(2021) Iqbal, Muhammad Arsalan; Ali, Asghar; Hadlich, Frieder; Oster, Michael; Reyer, Henry; Trakooljul, Nares; Sommerfeld, Vera; Rodehutscord, Markus; Wimmers, Klaus; Ponsuksili, Siriluck
Phosphorus (P) and calcium (Ca) are critical for egg production in laying hens. Most of P in plant-based poultry diet is bound as phytic acid and needs to be hydrolysed before absorption. To increase P bioavailability, exogenous phytases or bioavailable rock phosphate is added in feed. There is growing evidence of the importance of miRNAs as the epicentre of intestinal homeostasis and functional properties. Therefore, we demonstrated the expression of miRNA profiles and the corresponding target genes due to the different levels of P (recommended vs. 20% reduction) and/or Ca (recommended vs. 15% reduction) in feed. Jejunal miRNA profiles of Lohmann Selected Leghorn (LSL) and Lohmann Brown (LB) laying hens strains were used (n = 80). A total of 34 and 76 miRNAs were differentially expressed (DE) in the different diet groups within LSL and LB strains respectively. In LSL, the DE miRNAs and their targets were involved in calcium signaling pathway, inositol phosphate metabolism, and mitochondrial dysfunction. Similarly, in LB miRNAs targets were enriched in metabolic pathways such as glutathione metabolism, phosphonate metabolism and vitamin B6 metabolism. Our results suggest that both strains employ different intrinsic strategies to cope with modulated P and Ca supply and maintain mineral homeostasis.
Evaluation and method development for the biosynthesis of microbial lipopeptides by bacillus species
(2023) Vahidinasab, Maliheh; Hausmann, Rudolf
Microbial lipopeptides are secondary metabolites produced by bacteria and single-celled microorganisms. They consist of a cyclic or linear peptide chain linked to a lipid residue. Due to their high-foaming biosurfactant properties, they have various industrial applications such as in detergents, food emulsifiers, bioremediation, and enhanced oil recovery. Additionally, they possess other functional properties such as antifungal activity, making them an environmentally friendly alternative to synthetic fertilizers and fungicides. Bacillus species produce cyclic lipopeptides known for their potent antifungal activity, which makes them a potential source of bio-fungicides in agriculture. However, the production titer of wild-type Bacillus species does not meet industrial needs. Thereby, genetic modification of producer strains and bioprocess engineering can help increase the production of lipopeptides. Nevertheless, the regulation and basis of biosynthesis for Bacillus lipopeptides are still not completely understood, and ongoing research aims to enhance their production. In general, three main lipopeptide families, including surfactins, iturins, and fengycins are produced by different Bacillus species. Among these, surfactin as the strong biosurfactant is the most extensively studied lipopeptide produced by Bacillus species. The focus of this doctoral thesis was mainly to evaluate the biosynthesis of iturin and fengycin families, which are strong antimicrobial lipopeptides produced by Bacillus subtilis and Bacillus velezensis. This involved developing strains through genetic engineering and enhancing the lipopeptide titer by evaluating the cultivation medium. Initially, the entire genome of the bacteria used in this thesis was examined in terms of lipopeptide biosynthesis, and the structure and yield of the different produced lipopeptides were analyzed. Regarding the lipopeptide producer derivatives of the domesticated laboratory model strain B. subtilis 168 and B. subtilis 3NA, a spore deficient strain appropriate for bioreactor cultivation, surfactin is the lipopeptide with the highest yield, while plipastatin which is a member of fengycin family, is produced in lower quantities. In the present thesis, the biosynthesis of plipastatin by B. subtilis BMV9 as the lipopeptide producer derivative of strain 3NA was evaluated. The study aimed to convert BMV9 to a constitutive plipastatin mono-producer strain. In this sense, overexpressing plipastatin biosynthesis operon using the stronger constitutive Pveg promoter led to a five-fold increase in plipastatin production. Interestingly, it was observed that deletion of srfAA-AD operon in BMV9 and the constructed constitutive plipastatin producer strain has not improved plipastatin production. Therefore, it can be stated that presumably the biosynthesis of plipastatin may be positively influenced in a post-transcriptional manner by the surfactin synthetase or some of its subunits. However, the regulatory mechanism behind this effect remained unknown and requires further research. Another attempt to enhance the plipastatin biosynthesis in strain BMV9 was repairing the degQ expression. One main genome characterization of strains with B. subtilis 168 and 3NA background is that the pleiotropic degQ gene expression, which is known to have a positive effect on plipastatin biosynthesis, is silenced due to a mutation in the promoter area. However, while repair of degQ expression in BMV9 increased the plipastatin production, combination of both repaired degQ expression and promoter exchange (Ppps::Pveg) has not significantly increased the plipastatin yield. To further evaluate the impact of degQ expression on surfactin and plipastatin biosynthesis, two strains of B. subtilis were selected: JABs24, a lipopeptide producer derived from the 168 strain, and DSM10T, the wild-type strain expressing native degQ. The findings demonstrated that surfactin biosynthesis is negatively affected by DegQ-associated DegU regulation, while increased plipastatin biosynthesis is achieved in the presence of native degQ expression. In addition to production of lipopeptides, the DegU regulatory system also plays a role in the formation of secretory proteases. A comparison of extracellular protease activities between JABs24 and DSM10T showed that degQ expression led to DSM10T having five times higher protease activity than JABs24. Interestingly, production of extracellular proteases has not affected the stability of both plipastatin and surfactin during cultivation, suggesting that lipopeptides are less targeted by extracellular proteases. The identification of proficient wild-type strains is critical to the advancement of bio-fungicide in agriculture. Therefore, the subsequent approach of this thesis centered on the production of microbial lipopeptide by wild-type B. velezensis strains. Here, the lipopeptide productivity and antifungal ability of B. velezensis UTB96 was higher than B. velezensis FZB42, as a well-established strain for biocontrol of plant pathogens in agriculture. Furthermore, addition of certain amino acids stimulated lipopeptide production, and using a bioreactor system resulted in enhancement of lipopeptide production, especially iturin A by UTB96. Overall, the doctoral thesis evaluates the biosynthesis of antimicrobial lipopeptides produced by B. subtilis and B. velezensis. The study involves genetic engineering such as promoter exchange, deletion of genes involved in competing biosynthetic pathways and cultivation medium development with amino acid supplementation to enhance the lipopeptide titer. The thesis also identifies B. velezensis UTB96 as a promising candidate for further research to be used as a wild-type antifungal agent in agriculture.
Implementation and optimization of the doubled haploid technology for tropical maize (Zea mays L.) breeding programs
(2012) Prigge, Vanessa; Melchinger, Albrecht E.
Doubled haploid (DH) technology is currently the fastest way to achieve homozygosity in maize and it offers numerous quantitative genetic, operational, and economic advantages. Hybrid maize breeding with DH lines is common in temperate areas, yet adoption of this technology is still to be realized in tropical areas. Therefore, the main goal of my thesis project was to establish and validate the DH technology for tropical maize breeding programs at the International Maize and Wheat Improvement Center (CIMMYT) in Mexico. In vivo production of maternal haploids and DH lines involves four steps: (i) inducing haploidy by pollinating source germplasm with pollen of a haploid inducer; (ii) identifying seeds with haploid embryos based on a visually scorable marker; (iii) duplicating chromosomes of putative haploids by treating the seedlings with a mitotic inhibitor; and (iv) self-pollinating DH plants to multiply their seed. To impart knowledge on each of the above steps, we compiled a detailed protocol and produced a publicly available video which will be very useful for capacity building. Lack of reliable information on the performance of temperate inducers under nontemperate conditions is one reason for the slow adoption of DH technology in tropical maize breeding programs. Therefore, we assessed haploid induction rates (HIR) and agronomic performance of three temperate inducers in tropical lowland environments in Mexico. HIR obtained under tropical conditions were similar to those previously reported from evaluations under temperate conditions, indicating that temperate inducers can be used for initiation of DH breeding programs in the tropics. However, the inducers showed poor pollen production, poor seed set, and strong susceptibility to tropical leaf diseases. Hence, better adapted inducers would be advantageous for large-scale induction of haploidy in tropical DH programs. To develop better adapted haploid inducers, segregating populations were generated from crosses between temperate inducers and eight tropical CIMMYT maize lines (CML) from Mexico and Zimbabwe. Mass selection of individual F2 plants was conducted for visually scorable and highly heritable traits, followed by family-based selection for HIR and agronomic traits. Several tropical inducer candidates (TIC) were identified with HIR of up to 10% and notably improved agronomic performance under tropical lowland conditions. Compared to backcrosses to the inducers, backcrosses to the CML showed similar HIR combined with a significantly later anthesis date and improved plant vigor. Hence, backcrossing to the adapted parent may be a suitable approach to improve adaptation of new inducers while maintaining high HIR levels. Furthermore, we screened randomly chosen South American maize accessions and observed HIR of up to 3%, suggesting that novel sources of haploid induction ability may be present in CIMMYT?s vast germplasm collection. Although extensively exploited in DH line production, the genetic mechanisms underlying in vivo induction of maternal haploids in maize are still largely unknown. We conducted comparative quantitative trait locus (QTL) mapping for HIR to explore the genetic architecture of this phenomenon. Segregating populations were generated from four crosses composed of two temperate haploid inducer lines and three non-inducer lines. One major QTL on chromosome 1 (qhir1; bin 1.04) explaining up to 66% of the genotypic variance was detected in the three populations involving non-inducer lines. Hence, bin 1.04 represents an interesting region for map-based cloning. Further, qhir1 was affected by strong segregation distortion against the inducer allele, indicating that natural selection disfavors haploid induction ability. Seven QTL with smaller effects were detected in the CAUHOI×UH400 population. Further, we proposed a conceptual genetic framework for inheritance of in vivo haploid induction ability in maize. Common methods for artificial duplication of haploid chromosome sets mostly involve toxic and costly reagents and are extremely labor-intensive. This leads to serious bottlenecks during DH line development. When screening haploid populations derived from 260 diverse temperate and tropical source germplasm, we observed significant genetic variation for fertility-related traits, suggesting that haploid fertility can be effectively improved by recurrent selection. This may facilitate abolishment of artificial chromosome doubling during DH production, which seems particularly relevant for enabling small national maize breeding programs and seed companies in developing countries to adopt the DH technology. To study the suitability of different population types for DH line extraction, we developed 131 DH lines from five tropical elite single crosses (SC) and five tropical open-pollinated populations (OP) and evaluated them for testcross performance in Mexico. While testcross grain yield means of the two population types did not differ significantly, significant genetic variance was only revealed for OP-derived DH lines. Several DH lines from OP excelled in testcross performance and may be useful for tropical hybrid breeding programs. In addition, tropical OP may harbor valuable untapped genetic variation that can effectively be exploited with DH technology. This thesis work demonstrated that established protocols for in vivo DH line development can be readily applied to tropical maize breeding programs. Adoption of the DH technology promises to greatly increase the efficiency of breeding programs and DH lines are also an exciting tool to (i) immortalize genetic resources, (ii) conduct high-resolution genetic analyses of important traits, and (iii) accelerate the arrival of improved varieties to farmers? fields.
Production and employment impacts of new technologies : analysis for biotechnology
(2009) Wydra, Sven
Biotechnology is often regarded as a key technology with high potential for far-reaching social, environmental and economic impacts. Among others, the development and diffusion of biotechnology may have considerable economic effects on production and employment. This paper analyzes the economic impacts of different diffusion paths of biotechnology in some major application fields. Bottom-up technology information from literature, expert judgements and explicit scenario assumptions for various impact factors are combined and integrated in an input-output framework to calculate direct and indirect production and employment effects. The impact on net production and employment differs greatly between the different application sectors and depends on the respective importance of the various impact mechanisms. The indirect economic effects are rather high and exceed direct economic effects. These findings show the importance of a bottom-up approach as well as the consideration of indirect economic effects for appropriate analyses of the impact of biotechnology.
Quantitative Proteomanalyse von Pseudomonaden zur Aufklärung biotechnologisch relevanter Stoffwechselwege
(2013) Simon, Oliver; Huber, Armin
The main focus of this work was a quantitative proteome analysis of a variety of Pseudomonas strains with respect to the biotechnological synthesis of the base chemicals glyoxylic acid, butanol and vanillin. In addition, effects of the terpene citronellol on the proteome of P. aeruginosa were investigated. A second key aspect of this work involved the establishment of proteomics methods for the analysis of complex samples, especially for the analysis of membrane proteins. Using carbonate extraction followed by label-free MS-based quantification allowed the identification and quantification of a significant number of hydrophobic proteins which were not covered by the 2D-DIGE approach. In addition, the GeLCMSMS workflow was found to be a simple and efficient method for the analysis of total bacterial lysates. Using this method, about 30% of all proteins encoded by the P. putida KT2440 genome could be identified and quantified. In conclusion, this work demonstrated that different proteomics methods can substantially contribute to biotechnological strain development and the understanding of cellular networks.
Standard-setting and knowledge dynamics in innovation clusters
(2008) Christ, Julian P.; Slowak, André P.
Extensive research has been conducted on how firms and regions take advantage of spatially concentrated assets, and also why history matters to regional specialisation patterns. In brief, it seems that innovation clusters as a distinctive regional entity in international business and the geography of innovation are of increasing importance in STI policy, innovation systems and competitiveness studies. Recently, more and more research has contributed to an evolutionary perspective on collaboration in clusters. Nonetheless, the field of cluster or regional innovation systems remains a multidisciplinary field where the state of the art is determined by the individual perspective (key concepts could, for example, be industrial districts, innovative clusters with reference to OECD, regional knowledge production, milieus & sticky knowledge, regional lock-ins & path dependencies, learning regions or sectoral innovation systems). According to our analysis, the research gap lies in both quantitative, comparative surveys and in-depth concepts of knowledge dynamics and cluster evolution. Therefore this paper emphasises the unchallenged in-depth characteristics of knowledge utilisation within a cluster?s collaborative innovation activities. More precisely, it deals with knowledge dynamics in terms of matching different agents´ knowledge stocks via knowledge flows, common technology specification (standard-setting), and knowledge spillovers. The means of open innovation and system boundaries for spatially concentrated agents in terms of knowledge opportunities and the capabilities of each agent await clarification. Therefore, our study conceptualises the interplay between firm- and cluster-level activities and externalities for knowledge accumulation but also for the specification of technology. It remains particularly unclear how, why and by whom knowledge is aligned and ascribed to a specific sectoral innovation system. Empirically, this study contributes with several descriptive calculations of indices, e.g. knowledge stocks, GINI coefficients, Herfindahl indices, and Revealed Patent Advantage (RPA), which clearly underline a high spatial concentration of both mechanical engineering and biotechnology within a European NUTS2 sample for the last two decades. Conceptually, our paper matches the geography of innovation literature, innovation system theory, and new ideas related to the economics of standards. Therefore, it sheds light on the interplay between knowledge flows and externalities of cluster-specific populations and the agents? use of such knowledge, which is concentrated in space. We find that knowledge creation and standard-setting are cross-fertilising each other: although the spatial concentration of assets and high-skilled labour provides new opportunities to the firm, each firm?s knowledge stocks.need to be contextualised. The context in terms of ?use case? and ?knowledge biography? makes technologies (as represented in knowledge stocks) available for collaboration, but also clarifies relevance and ownership, in particular intellectual property concerns. Owing to this approach we propose a conceptualisation which contains both areas with inter- and intra-cluster focus. This proposal additionally concludes that spatial and technological proximity benefits standard-setting in high-tech and low-tech industries in very different ways. More precisely, the versatile tension between knowledge stocks, their evolution, and technical specification & implementation requires the conceptualisation and analysis of a non-linear process of standard-setting. Particularly, the use case of technologies is essential. Related to this approach, clusters strongly support the establishment of technology use cases in embryonic high-tech industries. Low-tech industries in contrast rather depend on approved knowledge stocks, whose dynamics provide better and fast accessible knowledge inputs within low-tech clusters.
Standard-setting and knowledge dynamics in innovation clusters
(2009) Christ, Julian P.; Slowak, André P.
Extensive research has been conducted on how firms and regions take advantage of spatially concentrated assets, and also why history matters to regional specialisation patterns. In brief, it seems that innovation clusters as a distinctive regional entity in international business and the geography of innovation are of increasing importance in STI policy, innovation systems and competitiveness studies. Recently, more and more research has contributed to an evolutionary perspective on collaboration in clusters. Nonetheless, the field of cluster or regional innovation systems remains a multidisciplinary field where the sate of the art is determined by the individual perspective (key concepts could, for example, be industrial districts, innovative clusters with reference to OECD, regional knowledge production, milieus & sticky knowledge, regional lock-ins & path dependencies, learning regions or sectoral innovation systems). According to our analysis, the research gap lies in both quantitative. comparative surveys and in-depth concepts of knowledge dynamics and cluster evolution. Therefore this paper emphasises the unchallenged in-depth characteristics of knowledge utilisation within a cluster's collaborative innovation activities. More precisely, it deals with knowledge dynamics in terms of matching different agents' knowledge stocks via knowledge flows, common technology specification (standard-setting), and knowledge spillovers. The means of open innovation and system boundaries for spatially concentrated agents in terms of knowledge opportunities and the capabilities of each agent await clarification. Therefore, our study conceptualises the interplay between firm- and cluster-level activities and externalities for knowledge accumulation but also for the specification of technology. It remains particularly unclear how, why and by whom knowledge is aligned and ascribed to a specific sectoral innovation system. Empirically, this study contributes with several descriptive calculations of indices, e.g. knowledge stocks, GINI coefficients, Herfindahl indices, and Revealed Patent Advantage (RPA). which clearly underline a high spatial concentration of both mechanical engineering and biotechnology within a European NUTS2 sample for the last two decades. Conceptually, our paper matches the geography of innovation literature, innovation system theory, and new ideas related to the economics of standards. Therefore. it sheds light on the interplay between knowledge flows and externalities of cluster-specific populations and the agents' use of such knowledge, which is concentrated in space. We find that knowledge creation and standard-setting are cross-fertilising each other: although the spatial concentration of assets and high-skilled labour provides new opportunities to the firm, each firm's knowledge stocks need to be contextualised. The context in terms of 'use case' and 'knowledge biography' makes technologies (as represented in knowledge stocks) available for collaboration, but also clarifies relevance and ownership, in particular intellectual property concerns. Owing to this approach we propose a conceptualisation which contains both areas with inter- and intra-cluster focus. This proposal additionally concludes that spatial and technological proximity benefits standard-setting in high-tech and low-tech industries in very different ways. More precisely, the versatile tension between knowledge stocks, their evolution. and technical specification & implementation requires the conceptualisation and analysis of a non-linear process of standard-setting. Particularly, the use case of technologies is essential. Related to this approach, clusters strongly support the establishment of technology use cases in embryonic high-tech industries. Low-tech industries in contrast rather depend on approved knowledge stocks, whose dynamics provide better and fast accessible knowledge inputs within low-tech clusters.
Strategic alliances, venture capital, and their roles before IPOs and M&As
(2020) Brinster, Leonhard; Tykvová, Tereza
The research objects of this dissertation are strategic alliances, venture capital (VC), and their roles before initial public offerings (IPOs) and mergers and acquisitions (M&As) of biotechnology and pharmaceutical companies. Chapter 1 begins this dissertation with a general introduction and the motivation behind the research questions. Young and small businesses face several risks and difficulties, such as lack of access to finance. Highly innovative companies, therefore, often rely on VC finance. Firms offering VC provide not only financial capital, monitoring, and coaching, but also other useful resources and might encourage their portfolio companies to join strategic alliances. Such alliances can be beneficial for the portfolio companies because they provide new knowledge, access to scarce resources, or other synergies. In addition, engagement in one or many strategic alliances can have a positive signaling effect on outsiders, and thus, increase the probabilities of a successful exit (IPO or M&A). In Chapter 2, I analyze the role of connected VC firms in strategic alliances. This chapter is co-authored with Tereza Tykvová. A reviewed version of this chapter is published in the Journal of Corporate Finance. We study a new channel through which portfolio companies benefit from ties among venture capitalists. By tracing individual VC firms’ investment and syndication histories, we show that VC firms’ ties improve companies’ access to strategic alliance partners. While existing studies demonstrate that alliances are more frequent among companies sharing the same VC firm, we provide evidence that alliances are also more prevalent among companies indirectly connected through VC syndication networks. In addition, our results suggest that VC firms’ ties mitigate asymmetric information problems that arise when alliances are formed. Finally, we demonstrate that this type of alliance is associated with higher IPO probabilities. We also provide alternative explanations of alliance formation and address related endogeneity concerns. The research objective of the third chapter is to determine the role of strategic alliances in VC exits. This chapter is co-authored with Christian Hopp and Tereza Tykvova. A reviewed version of this chapter is published in Venture Capital. Chapter 3 contributes to a better understanding of the relationship between strategic alliances and VC exits. The recent empirical literature concludes that alliances improve the probability of successful exits for venture-backed companies. When we control for observed and unobserved heterogeneity in a cohort sample of companies, self-selection into alliance activity, and censoring, we find the effect to be smaller than evidenced in prior studies. Moreover, we confirm the positive effect of alliances only for IPOs and not M&As. These findings are consistent with the view that strategic alliances help companies certify their quality for potential buyers. Chapter 4 investigates the role of strategic alliances before M&As in more detail. This chapter is a single-authored manuscript by Leonhard Brinster. Based on a large sample of M&A deals, I estimate the role of different types of ties between companies. I distinguish related alliances into direct and indirect alliances. Related alliances provide access to more information and can reduce transaction costs by reducing the time from announcement to completion of the M&A deal. The reduction of such costs can lead to a more successful target selection and increase the transaction process efficiency of the M&A deal. This effect can be explained by trust-building, better access to private information, and certification through related alliances. The empirical results show a positive relationship between related alliances and the likelihood of an M&A. However, in contrast to other studies, I do not find statistically significant evidence that supports the hypothesis that alliances increase the post-M&A performance and that alliances are associated with higher announcement returns. Finally, Chapter 5 concludes the dissertation with a short summary of the main findings and an outlook for future research.