<p>FBA was performed by optimizing biomass production and sequentially constraining to 0 ea... more <p>FBA was performed by optimizing biomass production and sequentially constraining to 0 each reaction in the corresponding simulations. The resulting growth rate was compared with the wild type one. Metabolic reactions were classified in three categories according to the relative growth rate obtained: Essential (E), partially-essential (PE) and non-essential (NE). X axis represent the fraction of each type of reactions in each category of E (in red), PE (in blue) and NE (in green). Reactions are distributed in 8 major subsystems (Y axis). Numbers between brackets indicate number of reactions in each group. Equivalent figures for oxygen limiting conditions and glycerol:methanol simulations can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0148031#pone.0148031.s001" target="_blank">S1 Fig</a>.</p
The yeast Pichia pastoris has emerged as one of the most promising yeast cell factories for the p... more The yeast Pichia pastoris has emerged as one of the most promising yeast cell factories for the production of heterologous proteins. The readily available genetic tools and the ease of high-cell density cultivations using methanol or glycerol/methanol mixtures are among the key factors for this development. Previous studies have shown that the use of mixed feeds of glycerol and methanol seem to alleviate the metabolic burden derived from protein production, allowing for higher specific and volumetric process productivities. However, initial studies of glycerol/methanol co-metabolism in P. pastoris by classical metabolic flux analyses using (13)C-derived Metabolic Flux Ratio (METAFoR) constraints were hampered by the reduced labelling information obtained when using C3:C1 substrate mixtures in relation to the conventional C6 substrate, that is, glucose. In this study, carbon flux distributions through the central metabolic pathways in glycerol/methanol co-assimilation conditions have been further characterised using biosynthetically directed fractional (13)C labelling. In particular, metabolic flux distributions were obtained under 3 different glycerol/methanol ratios and growth rates by iterative fitting of NMR-derived (13)C-labelling data from proteinogenic amino acids using the software tool (13)CFlux2. Specifically, cells were grown aerobically in chemostat cultures fed with 80:20, 60:40 and 40:60 (w:w) glycerol/methanol mixtures at two dilutions rates (0.05 hour(-1) and 0.16 hour(-1)), allowing to obtain additional data (biomass composition and extracellular fluxes) to complement pre-existing datasets. The performed (13)C-MFA reveals a significant redistribution of carbon fluxes in the central carbon metabolism as a result of the shift in the dilution rate, while the ratio of carbon sources has a lower impact on carbon flux distribution in cells growing at the same dilution rate. At low growth rate, the percentage of methanol directly dissimilated to CO2 ranges between 50% and 70%. At high growth rate the methanol is completely dissimilated to CO2 by the direct pathway, in the two conditions of highest methanol content.
High-level expression and secretion of heterologous proteins in yeast causes an increased energy ... more High-level expression and secretion of heterologous proteins in yeast causes an increased energy demand, which may result in altered metabolic flux distributions. Moreover, recombinant protein overproduction often results in ER-stress and oxidative stress, causing deviations from the optimal NAD(P)H regeneration balance. In this context, overexpression of genes encoding enzymes catalyzing endogenous NADPH producing reactions, such as the oxidative branch of the pentose phosphate pathway, has been previously shown to improve protein production in Pichia pastoris (syn. Komagataella spp). In this study, we evaluate the overexpression of the S. cerevisiae POS5-encoded NADH kinase in a recombinant P. pastoris strain as an alternative approach to overcome such redox constraints. Specifically, POS5 was co-overexpressed in a strain secreting an antibody fragment, either by directing Pos5 to the cytosol or to the mitochondria. The physiology of the resulting strains was evaluated in continuo...
The objectives of this research line, part of the CENIT-DEMETER project are organized in two sub-... more The objectives of this research line, part of the CENIT-DEMETER project are organized in two sub-lines, metabolic flux analysis applied to the conditions of the alcoholic fermentation of grape must, and control of S. cerevisiae nitrogen metabolism along the fermentation process. The final aim is to integrate experimental data in a model comprising all the steps of the fermentation, more comprehensive than those already available focused on fermentation kinetics or in a limited number of metabolites. This model might become a tool for the control of the fermentation, considering the effect of global warming on must composition; and would allow, among other possibilities, for the selection of the more suitable starter cultures according to must composition, or the rational use of enological additives (i.e. nitrogen nutrients). Finally, it would constitute a guide for selection procedures of new starters or, in the future, as a guide for metabolic engineering of industrial S. cerevisia...
The methylotrophic yeast Pichia pastoris (Komagataella phaffii) is currently considered one of th... more The methylotrophic yeast Pichia pastoris (Komagataella phaffii) is currently considered one of the most promising hosts for recombinant protein production (RPP) and metabolites due to the availability of several tools to efficiently regulate the recombinant expression, its ability to perform eukaryotic post-translational modifications and to secrete the product in the extracellular media. The challenge of improving the bioprocess efficiency can be faced from two main approaches: the strain engineering, which includes enhancements in the recombinant expression regulation as well as overcoming potential cell capacity bottlenecks; and the bioprocess engineering, focused on the development of rational-based efficient operational strategies. Understanding the effect of strain and operational improvements in bioprocess efficiency requires to attain a robust knowledge about the metabolic and physiological changes triggered into the cells. For this purpose, a number of studies have revealed chemostat cultures to provide a robust tool for accurate, reliable, and reproducible bioprocess characterization. It should involve the determination of key specific rates, productivities, and yields for different C and N sources, as well as optimizing media formulation and operating conditions. Furthermore, studies along the different levels of systems biology are usually performed also in chemostat cultures. Transcriptomic, proteomic and metabolic flux analysis, using different techniques like differential target gene expression, protein description and 13C-based metabolic flux analysis, are widely described as valued examples in the literature. In this scenario, the main advantage of a continuous operation relies on the quality of the homogeneous samples obtained under steady-state conditions, where both the metabolic and physiological status of the cells remain unaltered in an all-encompassing picture of the cell environment. This contribution aims to provide the state of the art of the different approaches that allow the design of rational strain and bioprocess engineering improvements in Pichia pastoris toward optimizing bioprocesses based on the results obtained in chemostat cultures. Interestingly, continuous cultivation is also currently emerging as an alternative operational mode in industrial biotechnology for implementing continuous process operations.
Pichia pastoris is recognized as a biotechnological workhorse for recombinant protein expression.... more Pichia pastoris is recognized as a biotechnological workhorse for recombinant protein expression. The metabolic performance of this microorganism depends on genetic makeup and culture conditions, amongst which the specific growth rate and oxygenation level are critical. Despite their importance, only their individual effects have been assessed so far, and thus their combined effects and metabolic consequences still remain to be elucidated. In this work, we present a comprehensive framework for revealing high-order (i.e., individual and combined) metabolic effects of the above parameters in glucose-limited continuous cultures of P. pastoris, using thaumatin production as a case study. Specifically, we employed a rational experimental design to calculate statistically significant metabolic effects from multiple chemostat data, which were later contextualized using a refined and highly predictive genome-scale metabolic model of this yeast under the simulated conditions. Our results revealed a negative effect of the oxygenation on the specific product formation rate (thaumatin), and a positive effect on the biomass yield. Notably, we identified a novel positive combined effect of both the specific growth rate and oxygenation level on the specific product formation rate. Finally, model predictions indicated an opposite relationship between the oxygenation level and the growth-associated maintenance energy (GAME) requirement, suggesting a linear GAME decrease of 0.56 mmol ATP/gDCW per each 1% increase in oxygenation level, which translated into a 44% higher metabolic cost under low oxygenation compared to high oxygenation. Overall, this work provides a systematic framework for mapping high-order metabolic effects of different culture parameters on the performance of a microbial cell factory. Particularly in this case, it provided valuable insights about optimal operational conditions for protein production in P. pastoris.
The increasing demand for recombinant proteins for a wide range of applications, from biopharmace... more The increasing demand for recombinant proteins for a wide range of applications, from biopharmaceutical protein complexes to industrial enzymes, is leading to important growth in this market. Among the different efficient host organism alternatives commonly used for protein production, the yeast Pichia pastoris (Komagataella phaffi) is currently considered to be one of the most effective and versatile expression platforms. The promising features of this cell factory are giving rise to interesting studies covering the different aspects that contribute to improving the bioprocess efficiency, from strain engineering to bioprocess engineering. The numerous drawbacks of using methanol in industrial processes are driving interest towards methanol-free alternatives, among which the GAP promoter-based systems stand out. The aim of this work is to present the most promising innovative developments in operational strategies based on rational approaches through bioprocess engineering tools. This rational design should be based on physiological characterization of the producing strains under bioprocess conditions and its interrelation with specific rates. This review focuses on understanding the key factors that can enhance recombinant protein production in Pichia pastoris; they are the basis for a further discussion on future industrial applications with the aim of developing scalable alternative strategies that maximize yields and productivity.
Metabolic flux analysis based on 13C-derived constraints has proved to be a powerful method for q... more Metabolic flux analysis based on 13C-derived constraints has proved to be a powerful method for quantitative physiological characterisation of one of the most extensively used microbial cell factory platforms, Pichia pastoris (syn. Komagataella spp.). Nonetheless, the reduced number of carbon atoms and the symmetry of the glycerol molecule has hampered the comprehensive determination of metabolic fluxes when used as the labelled C-source. Moreover, metabolic models typically used for 13C-based flux balance analysis may be incomplete or misrepresent the actual metabolic network. To circumvent these limitations, we reduced the genome-scale metabolic model iMT1026-v3.0 into a core model and used it for the iterative fitting of metabolic fluxes to the measured mass isotope distribution of proteinogenic amino acids obtained after fractional 13C labelling of cells with [1,3-13C]-glycerol. This workflow allows reliable estimates to be obtained for in vivo fluxes in P. pastoris cells growing on glycerol as sole carbon source, as well as revising previous assumptions concerning its metabolic operation, such as alternative metabolic branches, calculation of energetic parameters and proposed specific cofactor utilisation.
The methylotrophic yeast Pichia pastoris (Komagataella spp.) is widely used as cell factory for r... more The methylotrophic yeast Pichia pastoris (Komagataella spp.) is widely used as cell factory for recombinant protein production. In the past recent years, important breakthroughs in the systems-level quantitative analysis of its physiology have been achieved. This wealth of information has allowed the development of genome-scale metabolic models, which make new approaches possible for host cell and bioprocess engineering. Nevertheless, the predictive accuracy of the previous consensus model required to be upgraded and validated with new experimental data sets for P. pastoris growing on glycerol or methanol as sole carbon sources, two of the most relevant substrates for this cell factory. In this study, we have characterized P. pastoris growing in chemostat cultures using glycerol or methanol as sole carbon sources over a wide range of growth rates, thereby providing physiological data on the effect of growth rate and culture conditions on biomass macromolecular and elemental composit...
Azotobacter vinelandii is a bacterium that produces alginate and polyhydroxybutyrate (P3HB); howe... more Azotobacter vinelandii is a bacterium that produces alginate and polyhydroxybutyrate (P3HB); however, the role of NAD(P)H/NAD(P)+ ratios on the metabolic fluxes through biosynthesis pathways of these biopolymers remains unknown. The aim of this study was to evaluate the NAD(P)H/NAD(P) + ratios and the metabolic fluxes involved in alginate and P3HB biosynthesis, under oxygen-limiting and non-limiting oxygen conditions. The results reveal that changes in the oxygen availability have an important effect on the metabolic fluxes and intracellular NADPH/NADP+ ratio, showing that at the lowest OTR (2.4 mmol L-1 h-1), the flux through the tricarboxylic acid (TCA) cycle decreased 27.6-fold, but the flux through the P3HB biosynthesis increased 6.6-fold in contrast to the cultures without oxygen limitation (OTR = 14.6 mmol L-1 h-1). This was consistent with the increase in the level of transcription of phbB and the P3HB biosynthesis. In addition, under conditions without oxygen limitation, the...
The methanol-regulated alcohol oxidase promoter (PAOX1) of Pichia pastoris is one of the stronges... more The methanol-regulated alcohol oxidase promoter (PAOX1) of Pichia pastoris is one of the strongest promoters for heterologous gene expression in this methylotrophic yeast. Although increasing gene dosage is one of the most common strategies to increase recombinant protein productivities, the increase of gene dosage of Rhizopus oryzae lipase (ROL) in P. pastoris has been previously shown to reduce cell growth, lipase production and substrate consumption in high-copy strains. To better assess that physiological response, transcriptomics analysis was performed of a subset of strains with 1 to 15 ROL copies. The macroscopic physiological parameters confirm that growth yield and carbon uptake rate are gene dosage dependent, and were supported by the transcriptomic data, showing the impact of increased dosage of AOX1 promoter-regulated expression cassettes on P. pastoris physiology under steady methanolic growth conditions. Remarkably, increased number of cassettes led to transcription at...
Piscirickettsia salmonis is a fish bacterium that causes the disease piscirickettsiosis in salmon... more Piscirickettsia salmonis is a fish bacterium that causes the disease piscirickettsiosis in salmonids. This pathology is partially controlled by vaccines. The lack of knowledge has hindered its culture on laboratory and industrial scale. The study describes the metabolic phenotype of P. salmonis in culture. This study presents the first genome-scale model (iPF215) of the LF-89 strain of P. salmonis, describing the central metabolic pathway, biosynthesis and molecule degradation and transport mechanisms. The model was adjusted with experiment data, allowing the identification of the capacities that were not predicted by the automatic annotation of the genome sequences. The iPF215 model is comprised of 417 metabolites, 445 reactions and 215 genes, was used to reproduce the growth of P. salmonis (μmax 0.052±0.005h(-1)). The metabolic reconstruction of the P. salmonis LF-89 strain obtained in this research provides a baseline that describes the metabolic capacities of the bacterium and is the basis for developing improvements to its cultivation for vaccine formulation.
<p>FBA was performed by optimizing biomass production and sequentially constraining to 0 ea... more <p>FBA was performed by optimizing biomass production and sequentially constraining to 0 each reaction in the corresponding simulations. The resulting growth rate was compared with the wild type one. Metabolic reactions were classified in three categories according to the relative growth rate obtained: Essential (E), partially-essential (PE) and non-essential (NE). X axis represent the fraction of each type of reactions in each category of E (in red), PE (in blue) and NE (in green). Reactions are distributed in 8 major subsystems (Y axis). Numbers between brackets indicate number of reactions in each group. Equivalent figures for oxygen limiting conditions and glycerol:methanol simulations can be found in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0148031#pone.0148031.s001" target="_blank">S1 Fig</a>.</p
The yeast Pichia pastoris has emerged as one of the most promising yeast cell factories for the p... more The yeast Pichia pastoris has emerged as one of the most promising yeast cell factories for the production of heterologous proteins. The readily available genetic tools and the ease of high-cell density cultivations using methanol or glycerol/methanol mixtures are among the key factors for this development. Previous studies have shown that the use of mixed feeds of glycerol and methanol seem to alleviate the metabolic burden derived from protein production, allowing for higher specific and volumetric process productivities. However, initial studies of glycerol/methanol co-metabolism in P. pastoris by classical metabolic flux analyses using (13)C-derived Metabolic Flux Ratio (METAFoR) constraints were hampered by the reduced labelling information obtained when using C3:C1 substrate mixtures in relation to the conventional C6 substrate, that is, glucose. In this study, carbon flux distributions through the central metabolic pathways in glycerol/methanol co-assimilation conditions have been further characterised using biosynthetically directed fractional (13)C labelling. In particular, metabolic flux distributions were obtained under 3 different glycerol/methanol ratios and growth rates by iterative fitting of NMR-derived (13)C-labelling data from proteinogenic amino acids using the software tool (13)CFlux2. Specifically, cells were grown aerobically in chemostat cultures fed with 80:20, 60:40 and 40:60 (w:w) glycerol/methanol mixtures at two dilutions rates (0.05 hour(-1) and 0.16 hour(-1)), allowing to obtain additional data (biomass composition and extracellular fluxes) to complement pre-existing datasets. The performed (13)C-MFA reveals a significant redistribution of carbon fluxes in the central carbon metabolism as a result of the shift in the dilution rate, while the ratio of carbon sources has a lower impact on carbon flux distribution in cells growing at the same dilution rate. At low growth rate, the percentage of methanol directly dissimilated to CO2 ranges between 50% and 70%. At high growth rate the methanol is completely dissimilated to CO2 by the direct pathway, in the two conditions of highest methanol content.
High-level expression and secretion of heterologous proteins in yeast causes an increased energy ... more High-level expression and secretion of heterologous proteins in yeast causes an increased energy demand, which may result in altered metabolic flux distributions. Moreover, recombinant protein overproduction often results in ER-stress and oxidative stress, causing deviations from the optimal NAD(P)H regeneration balance. In this context, overexpression of genes encoding enzymes catalyzing endogenous NADPH producing reactions, such as the oxidative branch of the pentose phosphate pathway, has been previously shown to improve protein production in Pichia pastoris (syn. Komagataella spp). In this study, we evaluate the overexpression of the S. cerevisiae POS5-encoded NADH kinase in a recombinant P. pastoris strain as an alternative approach to overcome such redox constraints. Specifically, POS5 was co-overexpressed in a strain secreting an antibody fragment, either by directing Pos5 to the cytosol or to the mitochondria. The physiology of the resulting strains was evaluated in continuo...
The objectives of this research line, part of the CENIT-DEMETER project are organized in two sub-... more The objectives of this research line, part of the CENIT-DEMETER project are organized in two sub-lines, metabolic flux analysis applied to the conditions of the alcoholic fermentation of grape must, and control of S. cerevisiae nitrogen metabolism along the fermentation process. The final aim is to integrate experimental data in a model comprising all the steps of the fermentation, more comprehensive than those already available focused on fermentation kinetics or in a limited number of metabolites. This model might become a tool for the control of the fermentation, considering the effect of global warming on must composition; and would allow, among other possibilities, for the selection of the more suitable starter cultures according to must composition, or the rational use of enological additives (i.e. nitrogen nutrients). Finally, it would constitute a guide for selection procedures of new starters or, in the future, as a guide for metabolic engineering of industrial S. cerevisia...
The methylotrophic yeast Pichia pastoris (Komagataella phaffii) is currently considered one of th... more The methylotrophic yeast Pichia pastoris (Komagataella phaffii) is currently considered one of the most promising hosts for recombinant protein production (RPP) and metabolites due to the availability of several tools to efficiently regulate the recombinant expression, its ability to perform eukaryotic post-translational modifications and to secrete the product in the extracellular media. The challenge of improving the bioprocess efficiency can be faced from two main approaches: the strain engineering, which includes enhancements in the recombinant expression regulation as well as overcoming potential cell capacity bottlenecks; and the bioprocess engineering, focused on the development of rational-based efficient operational strategies. Understanding the effect of strain and operational improvements in bioprocess efficiency requires to attain a robust knowledge about the metabolic and physiological changes triggered into the cells. For this purpose, a number of studies have revealed chemostat cultures to provide a robust tool for accurate, reliable, and reproducible bioprocess characterization. It should involve the determination of key specific rates, productivities, and yields for different C and N sources, as well as optimizing media formulation and operating conditions. Furthermore, studies along the different levels of systems biology are usually performed also in chemostat cultures. Transcriptomic, proteomic and metabolic flux analysis, using different techniques like differential target gene expression, protein description and 13C-based metabolic flux analysis, are widely described as valued examples in the literature. In this scenario, the main advantage of a continuous operation relies on the quality of the homogeneous samples obtained under steady-state conditions, where both the metabolic and physiological status of the cells remain unaltered in an all-encompassing picture of the cell environment. This contribution aims to provide the state of the art of the different approaches that allow the design of rational strain and bioprocess engineering improvements in Pichia pastoris toward optimizing bioprocesses based on the results obtained in chemostat cultures. Interestingly, continuous cultivation is also currently emerging as an alternative operational mode in industrial biotechnology for implementing continuous process operations.
Pichia pastoris is recognized as a biotechnological workhorse for recombinant protein expression.... more Pichia pastoris is recognized as a biotechnological workhorse for recombinant protein expression. The metabolic performance of this microorganism depends on genetic makeup and culture conditions, amongst which the specific growth rate and oxygenation level are critical. Despite their importance, only their individual effects have been assessed so far, and thus their combined effects and metabolic consequences still remain to be elucidated. In this work, we present a comprehensive framework for revealing high-order (i.e., individual and combined) metabolic effects of the above parameters in glucose-limited continuous cultures of P. pastoris, using thaumatin production as a case study. Specifically, we employed a rational experimental design to calculate statistically significant metabolic effects from multiple chemostat data, which were later contextualized using a refined and highly predictive genome-scale metabolic model of this yeast under the simulated conditions. Our results revealed a negative effect of the oxygenation on the specific product formation rate (thaumatin), and a positive effect on the biomass yield. Notably, we identified a novel positive combined effect of both the specific growth rate and oxygenation level on the specific product formation rate. Finally, model predictions indicated an opposite relationship between the oxygenation level and the growth-associated maintenance energy (GAME) requirement, suggesting a linear GAME decrease of 0.56 mmol ATP/gDCW per each 1% increase in oxygenation level, which translated into a 44% higher metabolic cost under low oxygenation compared to high oxygenation. Overall, this work provides a systematic framework for mapping high-order metabolic effects of different culture parameters on the performance of a microbial cell factory. Particularly in this case, it provided valuable insights about optimal operational conditions for protein production in P. pastoris.
The increasing demand for recombinant proteins for a wide range of applications, from biopharmace... more The increasing demand for recombinant proteins for a wide range of applications, from biopharmaceutical protein complexes to industrial enzymes, is leading to important growth in this market. Among the different efficient host organism alternatives commonly used for protein production, the yeast Pichia pastoris (Komagataella phaffi) is currently considered to be one of the most effective and versatile expression platforms. The promising features of this cell factory are giving rise to interesting studies covering the different aspects that contribute to improving the bioprocess efficiency, from strain engineering to bioprocess engineering. The numerous drawbacks of using methanol in industrial processes are driving interest towards methanol-free alternatives, among which the GAP promoter-based systems stand out. The aim of this work is to present the most promising innovative developments in operational strategies based on rational approaches through bioprocess engineering tools. This rational design should be based on physiological characterization of the producing strains under bioprocess conditions and its interrelation with specific rates. This review focuses on understanding the key factors that can enhance recombinant protein production in Pichia pastoris; they are the basis for a further discussion on future industrial applications with the aim of developing scalable alternative strategies that maximize yields and productivity.
Metabolic flux analysis based on 13C-derived constraints has proved to be a powerful method for q... more Metabolic flux analysis based on 13C-derived constraints has proved to be a powerful method for quantitative physiological characterisation of one of the most extensively used microbial cell factory platforms, Pichia pastoris (syn. Komagataella spp.). Nonetheless, the reduced number of carbon atoms and the symmetry of the glycerol molecule has hampered the comprehensive determination of metabolic fluxes when used as the labelled C-source. Moreover, metabolic models typically used for 13C-based flux balance analysis may be incomplete or misrepresent the actual metabolic network. To circumvent these limitations, we reduced the genome-scale metabolic model iMT1026-v3.0 into a core model and used it for the iterative fitting of metabolic fluxes to the measured mass isotope distribution of proteinogenic amino acids obtained after fractional 13C labelling of cells with [1,3-13C]-glycerol. This workflow allows reliable estimates to be obtained for in vivo fluxes in P. pastoris cells growing on glycerol as sole carbon source, as well as revising previous assumptions concerning its metabolic operation, such as alternative metabolic branches, calculation of energetic parameters and proposed specific cofactor utilisation.
The methylotrophic yeast Pichia pastoris (Komagataella spp.) is widely used as cell factory for r... more The methylotrophic yeast Pichia pastoris (Komagataella spp.) is widely used as cell factory for recombinant protein production. In the past recent years, important breakthroughs in the systems-level quantitative analysis of its physiology have been achieved. This wealth of information has allowed the development of genome-scale metabolic models, which make new approaches possible for host cell and bioprocess engineering. Nevertheless, the predictive accuracy of the previous consensus model required to be upgraded and validated with new experimental data sets for P. pastoris growing on glycerol or methanol as sole carbon sources, two of the most relevant substrates for this cell factory. In this study, we have characterized P. pastoris growing in chemostat cultures using glycerol or methanol as sole carbon sources over a wide range of growth rates, thereby providing physiological data on the effect of growth rate and culture conditions on biomass macromolecular and elemental composit...
Azotobacter vinelandii is a bacterium that produces alginate and polyhydroxybutyrate (P3HB); howe... more Azotobacter vinelandii is a bacterium that produces alginate and polyhydroxybutyrate (P3HB); however, the role of NAD(P)H/NAD(P)+ ratios on the metabolic fluxes through biosynthesis pathways of these biopolymers remains unknown. The aim of this study was to evaluate the NAD(P)H/NAD(P) + ratios and the metabolic fluxes involved in alginate and P3HB biosynthesis, under oxygen-limiting and non-limiting oxygen conditions. The results reveal that changes in the oxygen availability have an important effect on the metabolic fluxes and intracellular NADPH/NADP+ ratio, showing that at the lowest OTR (2.4 mmol L-1 h-1), the flux through the tricarboxylic acid (TCA) cycle decreased 27.6-fold, but the flux through the P3HB biosynthesis increased 6.6-fold in contrast to the cultures without oxygen limitation (OTR = 14.6 mmol L-1 h-1). This was consistent with the increase in the level of transcription of phbB and the P3HB biosynthesis. In addition, under conditions without oxygen limitation, the...
The methanol-regulated alcohol oxidase promoter (PAOX1) of Pichia pastoris is one of the stronges... more The methanol-regulated alcohol oxidase promoter (PAOX1) of Pichia pastoris is one of the strongest promoters for heterologous gene expression in this methylotrophic yeast. Although increasing gene dosage is one of the most common strategies to increase recombinant protein productivities, the increase of gene dosage of Rhizopus oryzae lipase (ROL) in P. pastoris has been previously shown to reduce cell growth, lipase production and substrate consumption in high-copy strains. To better assess that physiological response, transcriptomics analysis was performed of a subset of strains with 1 to 15 ROL copies. The macroscopic physiological parameters confirm that growth yield and carbon uptake rate are gene dosage dependent, and were supported by the transcriptomic data, showing the impact of increased dosage of AOX1 promoter-regulated expression cassettes on P. pastoris physiology under steady methanolic growth conditions. Remarkably, increased number of cassettes led to transcription at...
Piscirickettsia salmonis is a fish bacterium that causes the disease piscirickettsiosis in salmon... more Piscirickettsia salmonis is a fish bacterium that causes the disease piscirickettsiosis in salmonids. This pathology is partially controlled by vaccines. The lack of knowledge has hindered its culture on laboratory and industrial scale. The study describes the metabolic phenotype of P. salmonis in culture. This study presents the first genome-scale model (iPF215) of the LF-89 strain of P. salmonis, describing the central metabolic pathway, biosynthesis and molecule degradation and transport mechanisms. The model was adjusted with experiment data, allowing the identification of the capacities that were not predicted by the automatic annotation of the genome sequences. The iPF215 model is comprised of 417 metabolites, 445 reactions and 215 genes, was used to reproduce the growth of P. salmonis (μmax 0.052±0.005h(-1)). The metabolic reconstruction of the P. salmonis LF-89 strain obtained in this research provides a baseline that describes the metabolic capacities of the bacterium and is the basis for developing improvements to its cultivation for vaccine formulation.
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Papers by Joan Albiol