Enhanced Fixation of CO2 in Land and Aquatic Biomass
Biomass, either terrestrial or aquatic, can efficiently fix CO2 from a variety of sources, such as the atmosphere, power plant and industrial exhaust gases, and soluble (hydrogen)carbonate salts thanks to the enzyme Ribulose-1,5-bisphosphate carboxylase/o
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Angela Dibenedetto
Abstract
Biomass, either terrestrial or aquatic, can efficiently fix CO2 from a variety of sources, such as the atmosphere, power plant and industrial exhaust gases, and soluble (hydrogen)carbonate salts thanks to the enzyme Ribulose-1,5bisphosphate carboxylase/oxygenase (RuBisCO). In addition to the carboxylation of ribulose that fixes CO2 into glucose (ca. 60%), used by the biomass as a source of energy and for building cellulose, RuBisCO also oxidizes the substrate (ca. 40%). Attempts have been made to engineer the enzyme for an enhanced carboxylation. Besides, efficient light-using organisms are under deep investigation. In particular, enhanced bio-fixation using microalgae has recently become an attractive approach to CO2 capture and C-recycling with a benefit derived from downstream utilization and application of the resulting microalgal biomass. This is a paradigmatic example of use of water and CO2 for stepping from the linear- to the circular-C-economy. It is of importance to select appropriate microalgal species that have a high growth rate, high CO2 fixation ability into valuable components, resistance to contaminants, low operation cost, and are easy to harvest and process. Strategies for the enhanced production of bioproducts and biofuels from microalgae, based on the manipulation of the strain physiology by controlling light, nutrient and other environmental conditions, which determine an efficient carbon conversion, are underway since long time. They are discussed in this Chapter together with an assessment of the value of the algal strain P. Tricornutum.
A. Dibenedetto (&) Department of Chemistry and CIRCC, University of Bari “Aldo Moro”, Bari, Italy e-mail: [email protected] © Springer Nature Switzerland AG 2019 M. Aresta et al. (eds.), An Economy Based on Carbon Dioxide and Water, https://doi.org/10.1007/978-3-030-15868-2_11
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A. Dibenedetto
Introduction
Photosynthesis uses CO2 and water for building a myriad of organics. Aquatic and terrestrial biomass absorb about 25% of carbon dioxide emissions during the Calvin cycle (a step of the photosynthesis process) where the enzyme Ribulose-1,5bisphosphate carboxylase/oxygenase (RuBisCO) (Fig. 11.1) catalyzes the reaction that turns ribulose and CO2 into glucose, used by the biomass as a source of energy and for building structural materials such as cellulose. RuBisCO, one of the most abundant enzymes in the biosphere, is a key enzyme in the global carbon cycle. It is defined a “slow enzyme”, in fact the turnover frequency of an average RuBisCO is only between 1 and 10 s−1 [1], representing a limiting factor in photosynthetic CO2-fixation under optimal conditions. In particular, the enzyme RuBisCO catalyzes the addition of gaseous carbon dioxide to ribulose-1,5-bisphosphate (1) (Scheme 11.1). The reaction gives two molecules of glycerate-3-phosphate (3). RuBisCO is also an error-prone enzyme (Scheme 11.1) (error rate: 20–40%) [2–4], since it can capture oxygen instead of CO2, slowing down the process of carbon
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