Single-cell biorefinery

A major challenge for the coproduction strategy is how to deal with carbon and/or energy competitive effects.To cope with these problems, strain- and process-based efforts should be performed to increase the supply of carbon and/or energy. For example, the metabolically connected S-adenosylmethionine (SAM) and glutathione were coproduced in yeast cells. However, both SAM and glutathione are biosynthesized via the consumption of ATP. To solve this problem, ATP-oriented amino acids and sodium 

There are several examples describing the production of multiple compounds from biomass, or its derived components (Table 9.2). Dairy manure is a type of biomass that contains 12% hemicellulose, 22% cellulose, and 18% crude protein, representing a lai e potential source of carbohydrates as a carbon source and proteins as a nitrc en source. This substrate is uniquely adaptable and advant eous for animal manure refineries. The Rhizopus oryzae ATCC 20344 cell factory produced fumaric acid and chitin fiom the dairy manure. A liquid/ solid separation was used to obtain a nitrc en-rich liquid stream for fungal growth and subsequent chitin accumulation, while the manure s solid stream, which primarily consisted of carbohydrates in the form of cellulose and hemicellulose, could be converted by various pretreatment methods into monosaccharides for fumaric acid production. 

A similar example is the coproduction of biocontrol and bioorganic fertilizer from low-cost substrate, soybean, and sweet potato residues during solid-state fermentation 

Escherichia coli Mixture containing glycerol/ glucose and fatty acid (by-product of biodiesel) Polyhydroxyalkano-ates and succinate 32 

Rhizopus oryzae Mixture containing hemicellulose, cellulose, and crude protein (animal manure refinery) Fumaric acid and chitin 86,87 

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Figure 9.1 The concept of single-cell biorefinery. A biorefinery is a facility that integrates biomass conversion processes and equipment to produce fuels, power, heat, and value-added chemicals from biomass. A single-cell biorefinery, in our views, is a single-cell factory that can produce multiple products from biomass or its various derived components. The orthogonal design of substrate-product metabolism does not interfere with the host cell s native interactome. Hence, the simultaneous production of different compound can be simply maximized by forward engineering principles with high accuracy of prediction.

Simultaneous substrate utilization is the prerequisite for single-cell biorefinery. The selected microbes must possess the possibility to utilize the multiple compounds in the substrate mixture or biomass hydrolysates. However, to design a single-cell biorefinery system, the coproduction in single cell is necessary. 

Table 9.2 Examples that fit the concept of single-cell biorefinery Strains Substrates Products...

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