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Development of Processing Strategies to Enhance the Efficiency of the Growth of the Gammaproteobacterial Methanotroph Methylomicrobium album BG8
- Author / Creator
- Bakhtiari Ziabari, Fatemeh
Methanotrophic bacteria can use different one-carbon compounds, including methane and methanol, two common industrial waste byproducts, as their main source of carbon and energy. Interestingly, they can convert these compounds into value-added products such as biofuels and bioplastics. Methanol is a common byproduct of the pulp and paper industry which is usually disposed of as waste. This leads to two issues: potential release in the environment can disturb and disrupt ecosystems, and the costs of disposal and loss of prospective revenues and economic concerns. Using methanotrophs, it is possible to produce high-value compounds from methanol while reducing its negative effects on the environment and the economic prospects of the industry. However, slow growth and low cell densities make the industrial implementation of methanotroph-based bioprocesses difficult. Increasing production and productivity is thus of utmost importance. To do so, bioprocessing strategies must be improved upon. In this study, different bioreactor operation strategies have been developed to improve the productivity for the growth of the gammaproteobacterial methanotroph Methylomicrobium album BG8 using methanol as the carbon source.
Copper is known to have a significant impact on the growth of methanotrophs feeding on methane through the regulation of the enzyme methane monooxygenase (MMO); however, its effect on M. album BG8 growing on methanol had not yet been determined. In this study, M. album BG8 was grown in batch cultures at a range of copper (from no supplementation to 0.3 mM supplemented) and methanol (from 8 to 150 mM). The highest optical densities were obtained when no copper was supplemented to the cultures, and copper addition was generally shown to negatively impact the growth rate. Thus, limiting copper supplementation below 0.01 mM at a methanol concentration of 25 mM was shown to provide optimal conditions for the growth (yield and titer) of M. album BG8.
In the second part of the study, various methanol-feeding strategies (pulsing fed-batch, step-wise fed-batch, varying target growth rate and initiation of feeding) were investigated to improve the growth and biomass productivity of M. album BG8 growing in fed-batch operation. These results were compared to growth in batch operation as a reference. The step-wise fed-batch operation with a target growth rate of 0.027 h-1 proved to have the highest biomass productivity (~0.027 ΔOD/h) while the step-wise fed-batch operation with a target growth rate of 0.0135 h-1 resulted in the highest final cell density achieved (6.6 compared to 0.35 in batch). Also, step-wise fed-batch and pulsing fed-batch operation significantly increased productivity compared to conventional batch (with increases of ~2.6 and 3-folds, respectively).
In the third part of this study, comparative metabolomics were used to investigate prospective commercially relevant metabolites produced by M. album BG8 growing on methanol in batch and fed-batch operations. Cultures were harvested in late exponential phase for batch, and at the end of controlled growth in fed-batch. Results showed that the mode of operation largely affected the abundance of metabolites of interest. Both batch and fed-batch operations resulted in bioproduction of commercially valuable metabolites; however, batch cultures led to greater abundance of metabolites linked to starvation and end-of-pathway (valine, leucine, and isoleucine), while fed-batch operation resulted in greater abundance of intermediates of metabolic pathways (e.g. 2,3-dihydroxy-isovalerate, 4-hydroxybenzoate, and phenyllactate).
This work provides a framework for the implementation of the methanotrophic bacterium M. album BG8 as an industrial platform organism for the production of industrially relevant bioproducts.
- Graduation date
- Spring 2021
- Type of Item
- Doctor of Philosophy
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