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Background: A representative hydrogen-oxidizing bacterium Cupriavidus necator H16 has attracted much attention as hosts to recycle carbon dioxide (CO2) into a biodegradable polymer, poly(R)-3-hydroxybutyrate (PHB). Although C. necator H16 has been used as a model PHB producer, the PHB production rate from CO2 is still too low for commercialization. Results: Here, we engineer the carbon fixation metabolism to improve CO2 utilization and increase PHB production. We explore the possibilities to enhance the lithoautotrophic cell growth and PHB production by introducing additional copies of transcriptional regulators involved in Calvin Benson Bassham (CBB) cycle. Both cbbR and regA-overexpressing strains showed the positive phenotypes for 11% increased biomass accumulation and 28% increased PHB production. The transcriptional changes of key genes involved in CO2—fixing metabolism and PHB production were investigated. Conclusions: The global transcriptional regulator RegA plays an important role in the regulation of carbon fixation and shows the possibility to improve autotrophic cell growth and PHB accumulation by increasing its expression level. This work represents another step forward in better understanding and improving the lithoautotrophic PHB production by C. necator H16. [ABSTRACT FROM AUTHOR]

Background: A representative hydrogen-oxidizing bacterium Cupriavidus necator H16 has attracted much attention as hosts to recycle carbon dioxide (CO2) into a biodegradable polymer, poly(R)-3-hydroxybutyrate (PHB). Although C. necator H16 has been used as a model PHB producer, the PHB production rate from CO2 is still too low for commercialization. Results: Here, we engineer the carbon fixation metabolism to improve CO2 utilization and increase PHB production. We explore the possibilities to enhance the lithoautotrophic cell growth and PHB production by introducing additional copies of transcriptional regulators involved in Calvin Benson Bassham (CBB) cycle. Both cbbR and regA-overexpressing strains showed the positive phenotypes for 11% increased biomass accumulation and 28% increased PHB production. The transcriptional changes of key genes involved in CO2—fixing metabolism and PHB production were investigated. Conclusions: The global transcriptional regulator RegA plays an important role in the regulation of carbon fixation and shows the possibility to improve autotrophic cell growth and PHB accumulation by increasing its expression level. This work represents another step forward in better understanding and improving the lithoautotrophic PHB production by C. necator H16. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass has considerable potential for the production of fuels and chemicals as a promising alternative to conventional fossil fuels. However, the bioconversion of lignocellulosic biomass to desired products must be improved to reach economic viability. One of the main technical hurdles is the presence of inhibitors in biomass hydrolysates, which hampers the bioconversion efficiency by biorefinery microbial platforms such as Saccharomyces cerevisiae in terms of both production yields and rates. In particular, acetic acid, a major inhibitor derived from lignocellulosic biomass, severely restrains the performance of engineered xylose‐utilizing S. cerevisiae strains, resulting in decreased cell growth, xylose utilization rate, and product yield. In this study, the robustness of XUSE, one of the best xylose‐utilizing strains, was improved for the efficient conversion of lignocellulosic biomass into bioethanol under the inhibitory condition of acetic acid stress. Through adaptive laboratory evolution, we successfully developed the evolved strain XUSAE57, which efficiently converted xylose to ethanol with high yields of 0.43–0.50 g ethanol/g xylose even under 2–5 g/L of acetic stress. XUSAE57 not only achieved twofold higher ethanol yields but also improved the xylose utilization rate by more than twofold compared to those of XUSE in the presence of 4 g/L of acetic acid. During fermentation of lignocellulosic hydrolysate, XUSAE57 simultaneously converted glucose and xylose with the highest ethanol yield reported to date (0.49 g ethanol/g sugars). This study demonstrates that the bioconversion of lignocellulosic biomass by an engineered strain could be significantly improved through adaptive laboratory evolution for acetate tolerance, which could help realize the development of an economically feasible lignocellulosic biorefinery to produce fuels and chemicals. [ABSTRACT FROM AUTHOR]

Background: A representative hydrogen-oxidizing bacterium Cupriavidus necator H16 has attracted much attention as hosts to recycle carbon dioxide (CO2) into a biodegradable polymer, poly(R)-3-hydroxybutyrate (PHB). Although C. necator H16 has been used as a model PHB producer, the PHB production rate from CO2 is still too low for commercialization. Results: Here, we engineer the carbon fixation metabolism to improve CO2 utilization and increase PHB production. We explore the possibilities to enhance the lithoautotrophic cell growth and PHB production by introducing additional copies of transcriptional regulators involved in Calvin Benson Bassham (CBB) cycle. Both cbbR and regA-overexpressing strains showed the positive phenotypes for 11% increased biomass accumulation and 28% increased PHB production. The transcriptional changes of key genes involved in CO2—fixing metabolism and PHB production were investigated. Conclusions: The global transcriptional regulator RegA plays an important role in the regulation of carbon fixation and shows the possibility to improve autotrophic cell growth and PHB accumulation by increasing its expression level. This work represents another step forward in better understanding and improving the lithoautotrophic PHB production by C. necator H16. [ABSTRACT FROM AUTHOR]

Background: A representative hydrogen-oxidizing bacterium Cupriavidus necator H16 has attracted much attention as hosts to recycle carbon dioxide (CO2) into a biodegradable polymer, poly(R)-3-hydroxybutyrate (PHB). Although C. necator H16 has been used as a model PHB producer, the PHB production rate from CO2 is still too low for commercialization. Results: Here, we engineer the carbon fixation metabolism to improve CO2 utilization and increase PHB production. We explore the possibilities to enhance the lithoautotrophic cell growth and PHB production by introducing additional copies of transcriptional regulators involved in Calvin Benson Bassham (CBB) cycle. Both cbbR and regA-overexpressing strains showed the positive phenotypes for 11% increased biomass accumulation and 28% increased PHB production. The transcriptional changes of key genes involved in CO2—fixing metabolism and PHB production were investigated. Conclusions: The global transcriptional regulator RegA plays an important role in the regulation of carbon fixation and shows the possibility to improve autotrophic cell growth and PHB accumulation by increasing its expression level. This work represents another step forward in better understanding and improving the lithoautotrophic PHB production by C. necator H16. [ABSTRACT FROM AUTHOR]