Microbial cell factories for bio-based biodegradable plastics production

Abstract

The misuse of petroleum-based plastics has resulted in serious environmental pollution and resource wastage. Biodegradable plastics can be used as green substitutes for traditional plastics. Here, we discuss the feasibility and technical bottlenecks in developing microbial cell factories for the production of biodegradable plastics from lignocellulosic wastes. First, we introduce the basic properties of the main biodegradable plastics on the market, including poly(lactic acid), poly(hydroxyalkanoate), and poly(butylene adipate-co-terephthalate). We then demonstrate the feasibility of synthesizing petroleum-based biodegradable plastic monomers from bio-based raw materials and propose strategies to further advance their commercial production through metabolic engineering and synthetic biology. We also analyze the main challenges facing the current development of bio-based biodegradable plastic biosynthesis technology. Finally, we discuss the current major lignocellulose bioconversion processes and explore way to further improve the utilization efficiency of the main carbohydrates in lignocellulosic hydrolysates by microorganisms, from the perspectives of sugar transport, sugar assimilation, and carbon catabolite inhibition.

Keywords: Applied microbiology; Biomass; Biotechnology; Microbiology.

Graphical abstract

Figure 1

Resource recycling economic scheme based on bio-based biodegradable plastics The microbial cell factory converts agricultural waste-derived lignocellulosic biomass into biodegradable plastics in an environmentally friendly manner. Agricultural wastes are recycled in the form of novel materials. Waste biodegradable plastics are biodegraded into compost to support crops, recycling this carbon back into nature.

Figure 2

Technical routes for commercial synthesis of biodegradable plastics Bio-based biodegradable plastics are mainly produced from glucose. The monomer 1,4-butanediol for petroleum-based biodegradable plastic PBAT can also be produced commercially from glucose, although current production processes using petroleum-based raw materials as substrates account for a considerable market share.

Figure 3

Various stages of bio-based production process development The development of the bio-based production process is divided into 5 stages. By establishing the biosynthetic pathway, improving production performance, expanding lignocellulose as available substrates, and enhancing the biotransformation efficiency of lignocellulose, an efficient production process is finally established using lignocellulosic biomass wastes as substrates.

Figure 4

Biosynthetic pathways of PHB, PHBV, P34HB, P3HB3HP, lactic acid, and PLA Different biosynthetic pathways are marked with different colors. GAP, glyceraldehyde 3-phosphate; DHAP, dihydroxyacetone phosphate; PEP, phosphoenolpyruvate; AcCoA, acetyl-CoA; α-KG, α-Ketoglutarate; PLA, poly(lactic acid); PHB, poly(β-hydroxybutyrate); PHBV, poly(hydroxybutyrate-co-valerate); P34HB, poly(3-hydroxybutyrate-co-4-hydroxybutyrate); P3HB3HP, poly(3-hydroxybutyrate-co-3-hydroxypropionat).

Figure 5

Major biosynthetic pathways of adipic acid and 1,4-butanediol Different biosynthetic pathways are marked with different colors. GAP, glyceraldehyde 3-phosphate; DHAP, dihydroxyacetone phosphate; PEP, phosphoenolpyruvate; AcCoA, acetyl-CoA; α-KG, α-Ketoglutarate.

Figure 6

Production models of 3 lignocellulose bioconversion processes SHF contains 4 steps of pretreatment, enzyme preparation, saccharification, and fermentation. SSF integrates saccharification and fermentation, while CBP integrates all 4 steps in 1 bioreactor. CBP, consolidated bioprocessing; SHF, separate hydrolysis and fermentation; SSF, simultaneous saccharification and fermentation.

Figure 7

Major carbohydrate utilization pathways of d-glucose, d-xylose, and l-arabinose Different carbohydrate utilization pathways are marked with different colors. GAP, glyceraldehyde 3-phosphate; DHAP, dihydroxyacetone phosphate; PEP, phosphoenolpyruvate; AcCoA, acetyl-CoA; α-KG, α-Ketoglutarate.