The use of fossil fuels in the aviation sector is accelerating global warming by emitting carbon dioxide into the atmosphere, calling for carbon neutral jet fuels. Unlike road transport, which is transitioning to electrification, aviation requires high-energy–density fuels, making liquid alternatives essential. Here we review the production of jet biofuels with emphasis on current production technologies, microbial engineering for lipid synthesis, catalytic conversion of lipids, and economic and life cycle assessment aspects. Microbial lipids, including free fatty acids, can be produced from various carbon sources such as sugars, lignocellulose, methane, methanol, and formate. Catalytic upgrading of lipids can be achieved by hydroprocessing, hydrodeoxygenation, hydrocracking, and hydroisomerization. Metabolic engineering strategies to enhance lipid biosynthesis include increasing the precursor supply, repressing β-oxidation, controlling fatty acid chain length, and applying systems-level optimization using flux balancing, biosensor-guided regulation, and evolutionary engineering. These strategies have enabled the production of 98.9 g lipids and 50 g free fatty acids per liter. Pichia pastoris employing methanol as a substrate can produce up to 23 g/L of free fatty acids. Catalytic upgrading via hydrodeoxygenation and hydrocracking achieves conversion efficiencies over 90

Methane (CH4) and carbon dioxide (CO2) are the dominant greenhouse gases (GHGs) that are increasing at an alarming rate. Methanotrophs have emerged as potential CH4 and CO2 biorefineries. This study demonstrated the synchronous incorporation of CH4 and CO2 into polyhydroxybutyrate (PHB) for the first time using 13C-labeling experiments in methanotrophs. By supplying substantial amounts of CO2, PHB content was enhanced in all investigated type II methanotrophic strains by 140 %, 146 %, and 162 %. The highest content of PHB from CH4 and CO2 in flask-scale cultivation reached 38 % dry cell weight in Methylocystis sp. MJC1, in which carbon percentage in PHB from CO2 was 45 %. Flux balance analysis predicted the critical roles of crotonyl-CoA carboxylase/reductase and phosphoenolpyruvate carboxylase in CO2 recycling. This study provided proof of the conversion of GHGs into a valuable and practical product using methanotrophic bacteria, contributing to addressing GHG emissions.

Methane is considered a promising carbon source in the field of biotechnology. Using methane as the carbon source for producing chemicals reduces manufacturing costs and tackles the issue of global warming. Like methane, lignocellulose biomass is also an inexpensive and ample carbon source, which could be used for in-dustrial biomanufacturing. In this study, Methylotuvimicrobium alcaliphilum 20Z was genetically modified to simultaneously consume methane and lignocellulose-derived sugars (glucose and xylose) to produce ectoine, a native osmoprotectant. The xylose utilization pathway, comprising xylA (xylose isomerase) and xylB (xyluloki-nase) genes from Escherichia coli, was first integrated into the chromosome of M. alcaliphilum 20Z. Further expression of the glucose utilization, consisting of glf (glucose facilitator) from Zymmonas mobilis, glk (endoge-nous glucokinase), and pgi (glucose 6-phosphate isomerase) from E. coli, made the engineered strain 20ZXG consume methane, xylose, and glucose concurrently. Cultivation on three substrates upregulated the Emb-den-Meyerhof-Parnas and ectoine biosynthesis pathways of 20Z. As a result, the ectoine content produced by 20ZXG grown on the three substrates was 1.7-fold enhanced compared with that obtained on methane solely. Furthermore, the knock-out of ectoine biosynthesis repressor (ectR1) led to an output of 37.93 +/- 3.27 mg/g-DCW, which was the highest quantity of ectoine produced after 48 h of cultivation in the presence of three substrates and was 2.3-fold higher than the initial output.

Methane is an important target for reducing greenhouse gases emission, owing to its abundance and highly global warming potential. Bioconversion of methane to value-added products, therefore, has become a promising and sustainable approach for industrial biomanufacturing. Herein, we metabolically engineered an obligate methanotroph Methylotuvimicrobium alcaliphilum 20Z to overproduce L-tryptophan and its derivative indole 3-acetic acid (IAA), a phytohormone, from methane. The engineered RS00 strain initially produced tryptophan from methane with a titer of 39.6 mg/L at 144 h of cultivation. The highest titer of IAA of 10.5 mg/L from methane was obtained in RS01 strain under Ptac promoter. Moreover, xylose, a carbon source derived from lignocellulosic biomass used as co-substrate, could enhance the titers of tryptophan and IAA in RS00 and RS01 strains by 60% and 82%, respectively. Remarkably, we proposed a proof-of-concept for the development of methanotroph-based plant growth-promoting bacteria (PGPB) which can utilize and convert methane into phytohormones to induce beneficial adaptation and growth promotion of plants. In this study, under saline-alkaline conditions, the germination percentage and elongation of the shoots and roots of wheat seeds treated with the IAA-producing strain were significantly improved, being 114%, 199% and 362% higher than those of control treatments, respectively. Our findings provide a novel methanotrophic platform for the conversion of renewable sources to value-added products. Additionally, the strategies and concepts presented here could be further expanded and applied to other methanotrophic hosts to develop biofertilizers that promote plant growth while mitigating methane and reducing chemical fertilizer use for sustainable agriculture production.

Methane and carbon dioxide (CO2) account for the most abundant greenhouse gases (GHGs). The removal of atmospheric methane and CO2 is an urgent mission contributing to the minimization of climate change. In this context, the methylotrophic bacteria-based technologies capturing and assimilating methane, CO2 and methane/CO2 derivatives, such as methanol and formate, are promising to reduce atmospheric methane and CO2. Herein, we emphasized the outstanding of methylotrophs in bioconversion of methane, CO2, methanol and formate, which are regarded as one-carbon (C1) substrates. Innovative strategies including co-substrate cultivation, power-generation reinforcement, and rational metabolic engineering for improving the efficiency of C1 bioconversion are highlighted. Additionally, we updated the advances in genetic tools to manipulate methylotrophs and discussed the possible applications of methylotrophs in sustainable agriculture. We believe that upgrading methylotrophic hosts towards efficient C1-conversion is a sustainable approach to achieving C1-based industrial manufacturing.

Methane and carbon dioxide (CO2) account for the most abundant greenhouse gases (GHGs). The removal of atmospheric methane and CO2 is an urgent mission contributing to the minimization of climate change. In this context, the methylotrophic bacteria-based technologies capturing and assimilating methane, CO2 and methane/ CO2 derivatives, such as methanol and formate, are promising to reduce atmospheric methane and CO2. Herein, we emphasized the outstanding of methylotrophs in bioconversion of methane, CO2, methanol and formate, which are regarded as one-carbon (C1) substrates. Innovative strategies including co-substrate cultivation, power-generation reinforcement, and rational metabolic engineering for improving the efficiency of C1 bioconversion are highlighted. Additionally, we updated the advances in genetic tools to manipulate methylotrophs and discussed the possible applications of methylotrophs in sustainable agriculture. We believe that upgrading methylotrophic hosts towards efficient C1-conversion is a sustainable approach to achieving C1-based industrial manufacturing.

A methanotroph-based production of natural compounds (indigo and α-farnesene) coupled with metabolic engineering strategies for unraveling bottlenecks in their biosynthesis pathways has been developed.

Sesquiterpenoids are one of the most diverse classes of isoprenoids which exhibit numerous potentials in industrial biotechnology. The methanotrophs-based methane bioconversion is a promising approach for sustainable production of chemicals and fuels from methane. With intrinsic high carbon flux though the ribulose monophosphate cycle in Methylotuvimicrobium alcaliphilum 20Z, we demonstrated here that employing a short-cut route from ribulose 5-phosphate to 1-deoxy-d-xylulose 5-phosphate (DXP) could enable a more efficient isoprenoid production via the methylerythritol 4-phosphate (MEP) pathway, using α-humulene as a model compound. An additional 2.8-fold increase in α-humulene production yield was achieved by the fusion of the nDXP enzyme and DXP reductase. Additionally, we utilized these engineering strategies for the production of another sesquiterpenoid, α-bisabolene. The synergy of the nDXP and MEP pathways improved the α-bisabolene titer up to 12.24 ± 0.43 mg/gDCW, twofold greater than that of the initial strain. This study expanded the suite of sesquiterpenoids that can be produced from methane and demonstrated the synergistic uses of the nDXP and MEP pathways for improving sesquiterpenoid production in methanotrophic bacteria.

5-aminolevulinic acid (ALA) has extensive use in photodynamic cancer therapy, tumor diagnosis, and agriculture. In the microbial production of ALA, most efforts have focused on engineering enzymes and the metabolic pathways involved in ALA biosynthesis. The aim of this study was to enhance ALA production using recombinant Streptomyces coelicolor expressing the ALA synthase gene (hem A) of Rhodobacter sphaeroides with a novel two-stage pH control strategy. Batch cultures were performed in production medium at different pH values. Although cells grew well at neutral pH (6.8–7.2), the highest amount of ALA was produced with a long culture time (140 h) at a weakly acidic pH (5.5–6.0). In response, a two-stage pH control strategy was developed in which pH was maintained at 6.8–7.2 for cell growth and then shifted to 5.5–6.0 to promote ALA synthesis, resulting in a significant enhancement in ALA production compared to a one-stage pH control strategy. The titer of ALA was further improved up to 482 mg/L in the two-stage pH culture by supplying more glucose in the medium and shifting the pH during the early phase of cultivation.

Riboswitches and toehold switches are considered to have potential for implementation in various fields, i.e., biosensing, metabolic engineering, and molecular diagnostics. The specific binding, programmability, and manipulability of these RNA-based molecules enable their intensive deployments in molecular detection as biosensors for regulating gene expressions, tracking metabolites, or detecting RNA sequences of pathogenic microorganisms. In this review, we will focus on the development of riboswitches and toehold switches in biosensing and molecular diagnostics. This review introduces the operating principles and the notable design features of riboswitches as well as toehold switches. Moreover, we will describe the advances and future directions of riboswitches and toehold switches in biosensing and molecular diagnostics.

Over the past two decades, intensive efforts have been made to construct recombinant Escherichia coli or Corynebacterium glutamicum by engineering C4 or C5 pathways to improve microbial production of 5-aminolevulinic acid (ALA), which has medical application for photodynamic cancer therapy and tumor diagnosis. In this study, we explored the feasibility of enhanced production of ALA by expressing C4 pathway enzyme, ALA synthase, in Streptomyces coelicolor, and medium optimization. The hemA from Rhodobacter sphaeroides was successfully integrated into the chromosome of Streptomyces coelicolor by conjugal transformation, and recombinant Streptomyces cells expressed well the foreign hemA. Glucose promoted ALA synthesis, and yeast extract showed a strong positive effect on ALA production. Optimization of casamino acid, peptone, malt extract, glycine, and succinic acid increased the product titer. In flask cultures, cell growth and ALA production of recombinant Streptomyces were 2.3 and 3.0-fold higher, respectively, in optimal medium than those of control. The maximum ALA, 137 mg/L, was obtained at 28 h in bioreactor culture, in which 3.1-fold higher cell mass and 2.9-fold greater volumetric productivity were achieved, compared to those in flask cultures.

Despite Polygonum multiflorum (PM) has been experiencely used as a drug to treat early graying hair phenomenon in Asian countries for a long time, there is limited study examined the real biological effects of PM on hair graying in vitro and in vivo. In this study, we investigated the effects of PM root extract (PM-RE) on melanin synthesis in human melanoma SKMEL-28 cells and embryos/larvae of wild-type strain AB zebrafish. We also preliminary revealed the molecular mechanism of early hair graying phenomenon in both in vitro and in vivo models. Our results showed that PM-RE significantly induced melanin synthesis in melanin-producing SKMEL-28 melanoma cells and also in zebrafish embryos/larvae at 4-day postfertilization through activation of MC1R/MITF/tyrosinase-signaling pathway. We also investigated the differences in genotype between graying hair follicle and black hair follicle of young peoples and found that early hair graying phenomenon may be related to downregulation of MC1R/MITF/tyrosinase pathway. Taken together, we suggested that PM-RE at safe doses could be used as a potential agent for the treatment of early hair graying and other loss pigmentation-related diseases.

지속 가능한 친환경 대체 연료인 바이오디젤은 국내·외적 으로 생산량이 꾸준히 증가하고 있다[38]. 바이오디젤 생산 공정에서 부산물로 발생되는 폐글리세롤 용액에는 지방산염 (약 20%), 반응 후 분리되지 않은 메탄올(약 11%) 및 염(나 트륨 또는 칼륨) 등의 불순물들이 상당 양 존재한다[30]. 최 근 들어 폐글리세롤이 과잉으로 발생하여 이를 정제하여 판 매하는 것이 가격 경쟁력을 상실하고 있을 뿐만 아니라 새 로운 환경오염 유발원으로 대두되어 바이오디젤 생산이 위 축되는 상황으로 변하고 있어 미국을 포함한 전 세계적으로 이의 처리 방안을 고심하고 있다[6, 38]. 따라서 폐글리세롤 을 고부가가치 유용물질로 전환하는 공정을 개발한다면 폐 글리세롤의 새로운 활용방안 창출을 통한 생산단가 절감은 물론 바이오디젤 생산의 활성화를 유도할 수 있다. 폐글리세 롤을 미생물 발효용 기질로 사용하여 바이오 연료(케미컬) 생산을 위한 많은 시도가 있었으나[4, 19, 32, 35], 다른 탄소 원을 사용하는 경우에 비하여 발효기간이 길고 생산성이 낮 다[4, 30, 35]. 이는 폐글리세롤에 존재하는 불순물들이 미생 물들의 생장을 억제하기 때문이다: 폐글리세롤 용액 중에 존 재하는 염 성분 들은 폐글리세롤 용액의 삼투압을 높이고[10, 17], 지방산 염은 그 자체가 독성물질로 작용하여 미생물의 생장을 저해한다[4, 21, 35]. 고온의 바이오디젤 생산공정에 Production of Aminolevulinic Acid by Recombinant Escherichia coli Co-expressing hemA and otsBA Using Crude Glycerol as Carbon Source Jingmei Yan1, Diep Ngoc Pham1, Dae-Kyung Kang2, Sung Bae Kim1, and Chang-Joon Kim1* 1Department of Chemical Engineering and ERI, Gyeongsang National University, Jinju 52828, Republic of Korea 2Department of Animal Resources Science, Dankook University, Cheonan 31116, Republic of Korea