Strategies for Biosynthesis of C1 Gas-derived Polyhydroxyalkanoates: A review.

Biosynthesis of polyhydroxyalkanoates (PHAs) from C1 gases is highly desirable in solving problems such as climate change and microplastic pollution. PHAs are biopolymers synthesized in microbial cells and can be used as alternatives to petroleum-based plastics because of their biodegradability. Because 50% of the cost of PHA production is due to organic carbon sources and salts, the utilization of costless C1 gases as carbon sources is expected to be a promising approach for PHA production. In this review, strategies for PHA production using C1 gases through fermentation and metabolic engineering are discussed. In particular, autotrophs, acetogens, and methanotrophs are strains that can produce PHA from CO2, CO, and CH4. In addition, integrated bioprocesses for the efficient utilization of C1 gases are introduced. Biorefinery processes from C1 gas into bioplastics are prospective strategies with promising potential and feasibility to alleviate environmental issues.

Poly-3-hydroxybutyrate production in acetate minimal medium using engineered Methylorubrum extorquens AM1.

Acetate is regarded as a sustainable microbial feedstock that is synthesized from biowastes such as synthesis gas (syngas), carbon dioxide, lignocellulose, or organic waste. In this study, Methylorubrum extorquens AM1 was engineered to improve the production of bioplastic poly-3-hydroxybutyrate (PHB) using acetate as the sole carbon source. To utilize acetate as a carbon source and methanol as an energy source, acs encoding acetyl-CoA synthetase and fdh from Burkholderia stabilis were overexpressed, while ftfL involved in the assimilation of methanol into formyl-tetrahydrofolate was deleted. The yields of biomass and PHB from acetate significantly improved, and the growth rate and PHB content of the bacteria increased. In addition, sustainability of the PHB production was demonstrated using acetate derived from carbon dioxide and syngas. This study shows that biopolymers could be synthesized efficiently using acetate as the sole carbon source through metabolic engineering and the supply of energy cofactors.

Synthesis and characterization of CLEA-lysozyme immobilized PS/PSMA nanofiber.

Using 0.2% glutaraldehyde as the cross-linker, lysozyme was covalently immobilized onto electrospun polystyrene/poly(styrene-co-maleic anhydride) (PS/PSMA) nanofibers as cross-linked enzyme aggregates (CLEA). The lysozyme capacity of PS/PSMA nanofibers under optimal condition was 57.6 mg/g of nanofibers. Various parameters were used to evaluate the stability of the immobilized CLEA-lysozyme. Compared to free enzyme, the immobilized CLEA-lysozyme exhibited its optimal enzymatic activity at higher temperature and pH. The immobilized CLEA-lysozyme maintained more than 78% of its initial activity during 30 days of storage period. Additionally, the immobilized CLEA-lysozyme presented a high antibacterial activity against Staphylococcus aureus. The durability determinations of such nanofibers showed 90.3% retention of the initial lysozyme activity after 80 consecutive reuses, and 81.2% of bacteriostasis ratio after 10 cycles. The results of this study suggest that CLEA-lysozyme immobilized nanofiber which can stabilize its enzymatic activity through cross-linking immobilization can be beneficial for various antibacterial processes.

Metabolic engineering of Methylorubrum extorquens AM1 for poly (3-hydroxybutyrate-co-3-hydroxyvalerate) production using formate.

Formate is a promising environmentally friendly and sustainable feedstock synthesized from syngas or carbon dioxide. Methylorubrum extorquens is a type II methylotroph that can use formate as a carbon source. It accumulates polyhydroxyalkanoates (PHAs) inside the cell, mainly producing poly-3-hydroxybutyrate (PHB), a degradable biopolymer. Owing to its high melting point and stiff nature, however, mechanical property improvement is warranted in the form of copolymerization. To produce the PHA copolymer, poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), the endogenous gene phaC was deleted and the pathway genes bktB, phaJ1, and phaC2, with broader substrate specificities, were heterologously expressed. To improve the incorporation of 3-hydroxyvalerate (3HV), the expression level of bktB was improved by untranslated region (UTR) engineering, and the endogenous gene phaA was deleted. The engineered M. extorquens produced PHBV with 8.9% 3HV using formate as the sole carbon source. In addition, when propionate and butyrate were supplemented, PHBVs with 3HV portions of up to 70.6% were produced. This study shows that a PHBV copolymer with a high proportion of 3HV can be synthesized using formate, a C1 carbon source, through metabolic engineering and supplementation with short-chain fatty acids.