Metabolic engineering of 1,2-propanediol production from cellobiose using beta-glucosidase-expressing E. coli

Engineering propionyl-CoA pools for de novo biosynthesis of odd-chain fatty acids in microbial cell factories

Odd-chain fatty acids (OcFAs) and their derivatives have attracted great interest due to their wide applications in the food, pharmaceutical and petrochemical industries. Microorganisms can naturally de novo produce fatty acids (FAs), where mainly, even-chain with acetyl-CoA instead of odd-chain with propionyl-CoA is used as the primer. Usually, the absence of the precursor propionyl-CoA is considered the main reason that limits the efficient production of OcFAs. It is thus crucial to explore/evaluate/identify promising propionyl-CoA biosynthetic pathways to achieve large-scale biosynthesis of OcFAs. This review discusses the latest advances in microbial metabolism engineering toward producing propionyl-CoA and considers future research directions and challenges toward optimized production of OcFAs.

Unraveling propylene glycol-induced lipolysis of the biosynthesis pathway in ultra-high temperature milk using high resolution mass spectrometry untargeted lipidomics and proteomics

In July 2022, the food safety accident that excessive propylene glycol was detected in milk processing factory raised widespread concerns about quality and nutrition of milk with illegal additive. To the best of our knowledge, the influences of propylene glycol to lipids in milk had not been systematically explored. Therefore, spatiotemporal distributions of lipids related to propylene glycol reaction and changes of sensory quality were investigated by food exogenous. Briefly, 10 subclasses (Cer, DG, HexCer, LPC, LPE, PC, PE, PI, SPH and TG) included 147 lipids and 38 pivotal enzymes were annotated. Propylene glycol altered lysophospholipidase and phospholipase A₂ through altering structural order in lipids domains surrounding proteins to inhibit glycerophospholipid metabolism and initiated obvious changes in PC (10.45-27.91 mg kg^-1) and PE (12.92-49.02 mg kg^-1). This study offered insights into influences of propylene glycol doses and storage time on milk metabolism at molecular level to assess the quality of milk.

Insights into C1 and C3 assimilation pathways in type I methanotrophic bacterium from co-production of 1,2-propanediol and lactate

Methanotrophic bacteria are attractive hosts for mining metabolic pathways of C1 assimilation to produce value-added products. Herein, the type I methanotroph Methylotuvimicrobium alcaliphilum 20Z was employed to explore the carbon flux from methane and methanol via the EMP pathway to produce 1,2-propanediol (1,2-PDO). The production of 1,2-PDO on methane was found to be mainly restricted by the lower carbon flux toward the EMP pathway. The co-utilization of C1 substrates and glycerol (C3) could contribute to enhance 1,2-PDO. Lactate was co-produced in much higher amounts than 1,2-PDO. This unexpected product was probably derived from lactaldehyde by inherent aldehyde dehydrogenases. The 1,2-PDO production without increased accumulation of lactate was observed via establishing the acetol-based pathway by propane utilization with the overexpression of pmoD. This is the first study to provide experimental insights into the operation of metabolic routes for 1,2-PDO and lactate co-production from C1 and C3 compounds in methanotrophs.

Rapid evolution and mechanism elucidation for efficient cellobiose-utilizing Saccharomyces cerevisiae through Synthetic Chromosome Rearrangement and Modification by LoxPsym-mediated Evolution

Lack of cellobiose utilization capability for many microorganisms results in carbon source waste in lignocellulosic biorefinery. In this study, genes for cellobiose transport and hydrolysis were introduced to Saccharomyces cerevisiae synV, a semi-synthetic yeast with an inducible SCRaMbLE (Synthetic Chromosome Rearrangement and Modification by LoxPsym-mediated Evolution) system incorporated into its chromosome V, endowing cellobiose utilization capability to this strain. Thereafter, two evolved strains with 98.1% and 79.2% improvement, respectively, in cellobiose utilization rate were obtained through induced SCRaMbLE. Further studies suggested that the enhanced cellobiose utilization capability directly correlated with copy number increases of introduced genes and some chromosome structural variations. In particular, it was experimentally demonstrated for the first time that deletion of redox stress related gene MXR1 and ATP conversion related gene ADK2 contributed to enhanced cellobiose conversion. Thereafter, the effectiveness of MXR1 and ADK2 deletions was demonstrated in artificial hydrolysate and rice straw hydrolysate, respectively.

Consolidated microbial production of four-, five-, and six-carbon organic acids from crop residues: Current status and perspectives

The production of platform organic acids has been heavily dependent on petroleum-based industries. However, petrochemical-based industries that cannot guarantee a virtuous cycle of carbons released during various processes are now facing obsolescence because of the depletion of finite fossil fuel reserves and associated environmental pollutions. Thus, the transition into a circular economy in terms of the carbon footprint has been evaluated with the development of efficient microbial cell factories using renewable feedstocks. Herein, the recent progress on bio-based production of organic acids with four-, five-, and six-carbon backbones, including butyric acid and 3-hydroxybutyric acid (C4), 5-aminolevulinic acid and citramalic acid (C5), and hexanoic acid (C6), is discussed. Then, the current research on the production of C4-C6 organic acids is illustrated to suggest future directions for developing crop-residue based consolidated bioprocessing of C4-C6 organic acids using host strains with tailor-made capabilities.

Active pharmaceutical ingredient (API) chemicals: a critical review of current biotechnological approaches

The aim of this article was to generate a framework of bio-based economy by an effective utilization of biomass from the perspectives of agriculture for developing potential end bio-based products (e.g. pharmaceuticals, active pharmaceutical ingredients). Our discussion is also extended to the conservatory ways of bioenergy along with development of bio-based products and biofuels. This review article further showcased the fundamental principles for producing these by-products. Thereby, the necessity of creating these products is to be efficaciously utilization by small-scale farmers that can aid the local needs for bio-based materials and energy. Concurrently, the building up of small markets will open up the avenues and linkages for bigger markets. In nutshell, the aim of the review is to explore the pathway of the biotechnological approaches so that less chosen producers and underdeveloped areas can be allied so that pressure on the systems of biomass production can be relaxed.

Distribution and Quantification of 1,2-Propylene Glycol Enantiomers in Baijiu

Enantiomers of 1,2-Propylene glycol (1,2-PG) were investigated in 64 commercial Chinese Baijiu including soy sauce aroma-type Baijiu (SSB), strong aroma-type Baijiu (STB), and light aroma-type Baijiu (LTB), via chiral gas chromatography (β-cyclodextrin). The natural enantiomeric distribution and concentration of 1,2-PG in various baijiu were studied to evaluate whether the distribution and content of the two isomers of 1,2-PG were correlated with the aroma type and storage year. The results showed that 1,2-PG has a high enantiomeric ratio and the (S)-configuration predominated in SSB. The average S/R enantiomeric ratio of this compound in SSB was approximately 87:13 (±3.17), with an average concentration of 52.77 (±23.70) mg/L for the (S)-configuration and 8.72 (±3.63) mg/L for the (R)-enantiomer. The (R)-configuration was predominant in the STB, whereas neither (S) nor (R)-form of 1,2-PG were detected in LTB. The content of the two configurations of 1,2-PG in the JSHSJ vintage of SSB showed a wave variation, with an average S/R enantiomeric ratio of 89:11 (±1.15). The concentration of (R)-1,2-PG in XJCTJ vintage liquors showed an upward and then downward trend with aging time, with an overall downward trend, and the concentration of (S)-form showed a wavy change with an overall upward trend. Except for the LZLJ-2019 vintage where both (R) and (S)-1,2-PG were present, all other samples only existed (R)-form, and a decreasing trend of (R)-enantiomer with aging time was observed. The enantiomeric ratio of 1,2-PG might be one of the potential markers for adulteration control of Baijiu as industrial 1,2-PG usually presented in the racemic mixture. Sensory analysis revealed olfactory thresholds of 4.66 mg/L and 23.92 mg/L for the (R)- and (S)-configurations in pure water respectively. GC-O showed both enantiomers exhibited different aromatic nuances.

Multiplex modification of Escherichia coli for enhanced β-alanine biosynthesis through metabolic engineering

β-Alanine is the only naturally occurring β-amino acid, widely used in the fine chemical and pharmaceutical fields. In this study, metabolic design strategies were attempted in Escherichia coli W3110 for enhancing β-alanine biosynthesis. Specifically, heterologous L-aspartate-α-decarboxylase was used, the aspartate kinase I and III involved in competitive pathways were down-regulated, the β-alanine uptake system was disrupted, the phosphoenolpyruvate carboxylase was overexpressed, and the isocitrate lyase repressor repressing glyoxylate cycle shunt was delete, the glucose uptake system was modified, and the regeneration of amino donor was up-regulated. On this basis, a plasmid harboring the heterologous panD and aspB was constructed. The resultant strain ALA17/pTrc99a-panD_BS-aspB_CG could yield 4.20 g/L β-alanine in shake flask and 43.94 g/L β-alanine (a yield of 0.20 g/g glucose) in 5-L bioreactor via fed-batch cultivation. These modification strategies were proved effective and the constructed β-alanine producer was a promising microbial cell factory for industrial production of β-alanine.

A comprehensive review on microbial production of 1,2-propanediol: micro-organisms, metabolic pathways, and metabolic engineering

1,2-Propanediol is an important building block as a component used in the manufacture of unsaturated polyester resin, antifreeze, biofuel, nonionic detergent, etc. Commercial production of 1,2-propanediol through microbial biosynthesis is limited by low efficiency, and chemical production of 1,2-propanediol requires petrochemically derived routes involving wasteful power consumption and high pollution emissions. With the development of various strategies based on metabolic engineering, a series of obstacles are expected to be overcome. This review provides an extensive overview of the progress in the microbial production of 1,2-propanediol, particularly the different micro-organisms used for 1,2-propanediol biosynthesis and microbial production pathways. In addition, outstanding challenges associated with microbial biosynthesis and feasible metabolic engineering strategies, as well as perspectives on the future microbial production of 1,2-propanediol, are discussed.