Genetic replacement of tesB with PTE1 affects chain-length proportions of 3-hydroxyalkanoic acids produced through β-oxidation of oleic acid in Escherichia coli

Engineering type I methanotrophic bacteria as novel platform for sustainable production of 3-hydroxybutyrate and biodegradable polyhydroxybutyrate from methane and xylose

Methylotuvimicrobium alcaliphilum20Z recombinant strain co-utilizing methane and xylose from anthropogenic activities and lignocellulose biomassis a promising cell factory platform. In this study, the production of (R)-3-hydroxybutyrate and poly (3-hydroxybutyrate) inM. alcaliphilum20Z was demonstrated. The production of (R)-3-hydroxybutyrate was optimized by introducing additional thioesterase, and a tunable genetic module. The final recombinant strain produced the highest titer of 334.52 ± 2 mg/L (R)-3-hydroxybutyrate (yield of 1,853 ± 429 mg/g dry cell weight). The poly (3-hydroxybutyrate) yielded 1.29 ± 0.08% (w/w) from methane and xylose in one-stage cultivation. Moreover, the study demonstrated the importance of pathway reversibility as an effective design strategy for balancing the driving force and intermediate accumulation. This is the first demonstration of the production ofbiodegradablepoly (3-hydroxybutyrate) from methane in type I methanotrophs, which is a key step toward sustainable biomanufacturing and carbon-neutral society.

Escherichia coli YigI is a Conserved Gammaproteobacterial Acyl-CoA Thioesterase Permitting Metabolism of Unusual Fatty Acid Substrates

Thioesterases play a critical role in metabolism, membrane biosynthesis, and overall homeostasis for all domains of life. In this present study, we characterize a putative thioesterase from Escherichia coli MG1655 and define its role as a cytosolic enzyme. Building on structure-guided functional predictions, we show that YigI is a medium- to long-chain acyl-CoA thioesterase that is involved in the degradation of conjugated linoleic acid (CLA) in vivo, showing overlapping specificity with two previously defined E. coli thioesterases TesB and FadM. We then bioinformatically identify the regulatory relationships that induce YigI expression, which include: an acidic environment, high oxygen availability, and exposure to aminoglycosides. Our findings define a role for YigI and shed light on why the E. coli genome harbors numerous thioesterases with closely related functions. IMPORTANCE Previous research has shown that long chain acyl-CoA thioesterases are needed for E. coli to grow in the presence of carbon sources such as conjugated linoleic acid, but that E. coli must possess at least one such enzyme that had not previously been characterized. Building off structure-guided function predictions, we showed that the poorly annotated protein YigI is indeed the previously unidentified third acyl CoA thioesterase. We found that the three potentially overlapping acyl-CoA thioesterases appear to be induced by nonoverlapping conditions and use that information as a starting point for identifying the precise reactions catalyzed by each such thioesterase, which is an important prerequisite for their industrial application and for more accurate metabolic modeling of E. coli.

Physiological activity of E. coli engineered to produce butyric acid

Faecalibacterium prausnitzii (F. prausnitzii) is one of the most abundant bacteria in the human intestine, with its anti-inflammatory effects establishing it as a major effector in human intestinal health. However, its extreme sensitivity to oxygen makes its cultivation and physiological study difficult. F. prausnitzii produces butyric acid, which is beneficial to human gut health. Butyric acid is a short-chain fatty acid (SCFA) produced by the fermentation of carbohydrates, such as dietary fibre in the large bowel. The genes encoding butyryl-CoA dehydrogenase (BCD) and butyryl-CoA:acetate CoA transferase (BUT) in F. prausnitzii were cloned and expressed in E. coli to determine the effect of butyric acid production on intestinal health using DSS-induced colitis model mice. The results from the E. coli Nissle 1917 strain, expressing BCD, BUT, or both, showed that BCD was essential, while BUT was dispensable for producing butyric acid. The effects of different carbon sources, such as glucose, N-acetylglucosamine (NAG), N-acetylgalactosamine (NAGA), and inulin, were compared with results showing that the optimal carbon sources for butyric acid production were NAG, a major component of mucin in the human intestine, and glucose. Furthermore, the anti-inflammatory effects of butyric acid production were tested by administering these strains to DSS-induced colitis model mice. The oral administration of the E. coli Nissle 1917 strain, carrying the expression vector for BCD and BUT (EcN-BCD-BUT), was found to prevent DSS-induced damage. Introduction of the BCD expression vector into E. coli Nissle 1917 led to increased butyric acid production, which improved the strain's health-beneficial effects.

Linoleic acid, α-linolenic acid, and monolinolenins as antibacterial substances in the heat-processed soybean fermented with Rhizopus oligosporus

Antibacterial activities against Staphylococcus aureus and Bacillus subtilis were found in an ethanol fraction of tempe, an Indonesian fermented soybean produced using Rhizopus oligosporus. The ethanol fraction contained free fatty acids, monoglycerides, and fatty acid ethyl esters. Among these substances, linoleic acid and α-linolenic acid exhibited antibacterial activities against S. aureus and B. subtilis, whereas 1-monolinolenin and 2-monolinolenin exhibited antibacterial activity against B. subtilis. The other free fatty acids, 1-monoolein, monolinoleins, ethyl linoleate, and ethyl linolenate did not exhibit bactericidal activities. These results revealed that R. oligosporus produced the long-chain polyunsaturated fatty acids and monolinolenins as antibacterial substances against the Gram-positive bacteria during the fungal growth and fermentation of heat-processed soybean.

A balanced ATP driving force module for enhancing photosynthetic biosynthesis of 3-hydroxybutyrate from CO2

Using engineered photoautotrophic microorganisms for the direct chemical synthesis from CO₂ is an attractive direction for both sustainability and CO₂ mitigation. However, the behaviors of non-native metabolic pathways may be difficult to control due to the different intracellular contexts between natural and heterologous hosts. While most metabolic engineering efforts focus on strengthening driving forces in pathway design to favor biochemical production in these organisms, excessive driving force may be detrimental to product biosynthesis due to imbalanced cellular intermediate distribution. In this study, an ATP-hydrolysis based driving force module was engineered into cyanobacterium Synechococcus elongatus PCC 7942 to produce 3-hydroxybutyrate (3HB), a valuable chemical feedstock for the synthesis of biodegradable plastics and antibiotics. However, while the ATP driving force module is effective for increasing product formation, uncontrolled accumulation of intermediate metabolites likely led to metabolic imbalance and thus to cell growth inhibition. Therefore, the ATP driving force module was reengineered by providing a reversible outlet for excessive carbon flux. Upon expression of this balanced ATP driving force module with 3HB biosynthesis, engineered strain produced 3HB with a cumulative titer of 1.2 g/L, a significant increase over the initial strain. This result highlighted the importance of pathway reversibility as an effective design strategy for balancing driving force and intermediate accumulation, thereby achieving a self-regulated control for increased net flux towards product biosynthesis.

Effect of increased feeding of dietary α-linolenic acid by grazing on formation of the cis9,trans11-18:2 isoform of conjugated linoleic acid in bovine milk

Feeding systems such as grazing affect the fatty acid profile of bovine milk fat. In addition, milk fat is formed as the product of fatty acid metabolism in cow bodies before being secreted into milk. However, how grazing influences milk fatty acid profile through the metabolism has not been completely characterized. When fatty acid concentrations in Holstein milk were compared between grazing and non-grazing periods, α-linolenic acid was significantly higher in the grazing period than in the non-grazing period. This could be explained with an increase in α-linolenic acid feeding with grazing. α-linolenic acid had a linear positive correlation with conjugated linoleic acid (9c,11t-18:2) (CLA) and vaccenic acid (VA) during the grazing period, whereas CLA had higher correlation with linoleic acid rather than with α-linolenic acid during the non-grazing period. These data indicate that the high content of dietary α-linolenic acid affects CLA and VA formation in milk of grazing periods via α-linolenic acid metabolism into VA.

Synthesis of polyhydroxyalkanoates from glucose that contain medium-chain-length monomers via the reversed fatty acid β-oxidation cycle in Escherichia coli

Polyhydroxyalkanoates that contain the medium-chain-length monomers (mcl-PHAs) have a wide range of applications owing to their superior physical and mechanical properties. A challenge to synthesize such mcl-PHAs from unrelated and renewable sources is exploiting the efficient metabolic pathways that lead to the formation of precursor (R)-3-hydroxyacyl-CoA. Here, by engineering the reversed fatty acid β-oxidation cycle, we were able to synthesize mcl-PHAs in Escherichia coli directly from glucose. After deletion of the major thioesterases, the engineered E. coli produced 6.62wt% of cell dry weight mcl-PHA heteropolymers. Furthermore, when a low-substrate-specificity PHA synthase from Pseudomonas stutzeri 1317 was employed, recombinant E. coli synthesized 12.10wt% of cell dry weight scl-mcl PHA copolymers, of which 21.18mol% was 3-hydroxybutyrate and 78.82mol% was medium-chain-length monomers. The reversed fatty acid β-oxidation cycle offered an efficient metabolic pathway for mcl-PHA biosynthesis in E. coli and can be further optimized.

Regulation of peroxisomal lipid metabolism: the role of acyl-CoA and coenzyme A metabolizing enzymes

Peroxisomes are nearly ubiquitous organelles involved in a number of metabolic pathways that vary between organisms and tissues. A common metabolic function in mammals is the partial degradation of various (di)carboxylic acids via α- and β-oxidation. While only a small number of enzymes catalyze the reactions of β-oxidation, numerous auxiliary enzymes have been identified to be involved in uptake of fatty acids and cofactors required for β-oxidation, regulation of β-oxidation and transport of metabolites across the membrane. These proteins include membrane transporters/channels, acyl-CoA thioesterases, acyl-CoA:amino acid N-acyltransferases, carnitine acyltransferases and nudix hydrolases. Here we review the current view of the role of these auxiliary enzymes in peroxisomal lipid metabolism and propose that they function in concert to provide a means to regulate fatty acid metabolism and transport of products across the peroxisomal membrane.