Translating advances in microbial bioproduction to sustainable biotechnology

Towards consolidated bioprocessing of biomass and plastic substrates for semi-synthetic production of bio-poly(ethylene furanoate) (PEF) polymer using omics-guided construction of artificial microbial consortia

Poly(ethylene furanoate) (PEF) plastic is a 100% renewable polyester that is currently being pursued for commercialization as the next-generation bio-based plastic. This is in line with growing demand for circular bioeconomy and new plastics economy that is aimed at minimizing plastic waste mismanagement and lowering carbon footprint of plastics. However, the current catalytic route for the synthesis of PEF is impeded with technical challenges including high cost of pretreatment and catalyst refurbishment. On the other hand, the semi-biosynthetic route of PEF plastic production is of increased biotechnological interest. In particular, the PEF monomers (Furan dicarboxylic acid and ethylene glycol) can be synthesized via microbial-based biorefinery and purified for subsequent catalyst-mediated polycondensation into PEF. Several bioengineering and bioprocessing issues such as efficient substrate utilization and pathway optimization need to be addressed prior to establishing industrial-scale production of the monomers. This review highlights current advances in semi-biosynthetic production of PEF monomers using consolidated waste biorefinery strategies, with an emphasis on the employment of omics-driven systems biology approaches in enzyme discovery and pathway construction. The roles of microbial protein transporters will be discussed, especially in terms of improving substrate uptake and utilization from lignocellulosic biomass, as well as from depolymerized plastic waste as potential bio-feedstock. The employment of artificial bioengineered microbial consortia will also be highlighted to provide streamlined systems and synthetic biology strategies for bio-based PEF monomer production using both plant biomass and plastic-derived substrates, which are important for circular and new plastics economy advances.

Exergetic analysis and optimization of process variables in xylitol production: Maximizing efficiency and sustainability in biotechnological processes

This study presents an exergetic analysis of xylitol fermentative production from hemicellulose hydrolysate, aiming to optimize operational conditions in a fluidized bed bioreactor. The aerobic fermentation conditions evaluated in this study (gas flow rate - x1, hydrolysate concentration factor - x2, and recirculation flow rate - x3) were optimized using various exergetic parameters and xylitol yield as objective functions. Four objective functions were defined for the mono-objective optimization process: rational exergetic efficiency, normalized destroyed exergy, thermodynamic sustainability index, and xylitol yield factor. The results reveal that the optimization problem involves conflicting objectives when considering both yield-based and exergy-based approaches. Thus, the bioreactor's performance was formulated as a multi-objective problem, where the yield factor and thermodynamic sustainability index were simultaneously maximized. For the multi-objective optimization, the ideal operational variable ranges were found to be: 594 ≤x1≤ 619 mL/min, x2= 7 e 37 ≤x3≤ 57 L/h.

Enhancing 3-hydroxypropionic acid production in Saccharomyces cerevisiae through enzyme localization within mitochondria

Microbial 3-hydroxypropionic acid (3-HP) production can potentially replace petroleum-based production methods for acrylic acid. Here, we constructed a yeast strain that expressed enzymes related to 3-HP biosynthesis within the mitochondria. This approach aimed to enhance the 3-HP production by utilizing the mitochondrial acetyl-CoA, an important intermediate for synthesizing 3-HP. The strain that expressed 3-HP-producing enzymes in the mitochondria (YPH-mtA3HP) showed improved production of 3-HP compared to that shown by the strain expressing 3-HP-producing enzymes in the cytosol (YPH-cyA3HP). Additionally, cMCR was overexpressed, which regulates a rate-limiting reaction in synthesizing 3-HP. In this study, we aimed to further enhance 3-HP production by expressing multiple copies of cMCR in the mitochondria using the δ-integration strategy to optimize the expression level of cMCR (YPH-mtA3HPx*). The results of flask-scale cultivation showed that 3-HP production by cMCR δ-integration was significantly higher, exhibiting a yield of 160 mg/L in YPH-mtA3HP6* strain and 257 mg/L in YPH-mtA3HP22* strain. Notably, YPH-mtA3HP22*, exhibited the highest 3-HP titer, which was 3.2-fold higher than that of YPH-cyA3HP. Our results demonstrated the potential of utilizing the mitochondrial compartment within S. cerevisiae for enhancing 3-HP production.