Functional Analysis of Deoxyhexose Sugar Utilization in Escherichia coli Reveals Fermentative Metabolism under Aerobic Conditions

Systems Metabolic Engineering to Elucidate and Enhance Intestinal Metabolic Activities of Escherichia coli Nissle 1917

Escherichia coli Nissle 1917 (EcN) is one of the most widely used probiotics to treat gastrointestinal diseases. Recently, many studies have engineered EcN to release therapeutic proteins to treat specific diseases. However, because EcN exhibits intestinal metabolic activities, it is difficult to predict outcomes after administration. In silico and fermentation profiles revealed mucin metabolism of EcN. Multiomics revealed that fucose metabolism contributes to the intestinal colonization of EcN by enhancing the synthesis of flagella and nutrient uptake. The multiomics results also revealed that excessive intracellular trehalose synthesis in EcN, which is responsible for galactose metabolism, acts as a metabolic bottleneck, adversely affecting growth. To improve the ability of EcN to metabolize galactose, otsAB genes for trehalose synthesis were deleted, resulting in the ΔotsAB strain; the ΔotsAB strain exhibited a 1.47-fold increase in the growth rate and a 1.37-fold increase in the substrate consumption rate relative to wild-type EcN.

L-Fucose is involved in human-gut microbiome interactions

L-Fucose is one of the key metabolites in human-gut microbiome interactions. It is continuously synthesized by humans in the form of fucosylated glycans and fucosyl-oligosaccharides and delivered into the gut throughout their lifetime. Gut microorganisms metabolize L-fucose and produce short-chain fatty acids, which are absorbed by epithelial cells and used as energy sources or signaling molecules. Recent studies have revealed that the carbon flux in L-fucose metabolism by gut microorganisms is distinct from that in other sugar metabolisms because of cofactor imbalance and low efficiencies in energy synthesis of L-fucose metabolism. The large amounts of short-chain fatty acids produced during microbial L-fucose metabolism are used by epithelial cells to recover most of the energy used up during L-fucose synthesis. In this review, we present a detailed overview of microbial L-fucose metabolism and a potential solution for disease treatment and prevention using genetically engineered probiotics that modulate fucose metabolism. Our review contributes to the understanding of human-gut microbiome interactions through L-fucose metabolism. KEY POINTS: • Fucose-metabolizing microorganisms produce large amounts of short-chain fatty acids • Fucose metabolism differs from other sugar metabolisms by cofactor imbalance • Modulating fucose metabolism is the key to control host-gut microbiome interactions.

Developing a Fluorescent Inducible System for Free Fucose Quantification in Escherichia coli

L-Fucose is a monosaccharide abundant in mammalian glycoconjugates. In humans, fucose can be found in human milk oligosaccharides (HMOs), mucins, and glycoproteins in the intestinal epithelium. The bacterial consumption of fucose and fucosylated HMOs is critical in the gut microbiome assembly of infants, dominated by Bifidobacterium. Fucose metabolism is important for the production of short-chain fatty acids and is involved in cross-feeding microbial interactions. Methods for assessing fucose concentrations in complex media are lacking. Here we designed and developed a molecular quantification method of free fucose using fluorescent Escherichia coli. For this, low- and high-copy plasmids were evaluated with and without the transcription factor fucR and its respective fucose-inducible promoter controlling the reporter gene sfGFP. E. coli BL21 transformed with a high copy plasmid containing pFuc and fucR displayed a high resolution across increasing fucose concentrations and high fluorescence/OD values after 18 h. The molecular circuit was specific against other monosaccharides and showed a linear response in the 0-45 mM range. Adjusting data to the Hill equation suggested non-cooperative, simple regulation of FucR to its promoter. Finally, the biosensor was tested on different concentrations of free fucose and the supernatant of Bifidobacterium bifidum JCM 1254 supplemented with 2-fucosyl lactose, indicating the applicability of the method in detecting free fucose. In conclusion, a bacterial biosensor of fucose was validated with good sensitivity and precision. A biological method for quantifying fucose could be useful for nutraceutical and microbiological applications, as well as molecular diagnostics.

High-Fructose Diet Alters Intestinal Microbial Profile and Correlates with Early Tumorigenesis in a Mouse Model of Barrett’s Esophagus

Esophageal adenocarcinoma (EAC) is mostly prevalent in industrialized countries and has been associated with obesity, commonly linked with a diet rich in fat and refined sugars containing high fructose concentrations. In meta-organisms, dietary components are digested and metabolized by the host and its gut microbiota. Fructose has been shown to induce proliferation and cell growth in pancreas and colon cancer cell lines and also alter the gut microbiota. In a previous study with the L2-IL-1B mouse model, we showed that a high-fat diet (HFD) accelerated EAC progression from its precursor lesion Barrett’s esophagus (BE) through changes in the gut microbiota. Aiming to investigate whether a high-fructose diet (HFrD) also alters the gut microbiota and favors EAC carcinogenesis, we assessed the effects of HFrD on the phenotype and intestinal microbial communities of L2-IL1B mice. Results showed a moderate acceleration in histologic disease progression, a mild effect on the systemic inflammatory response, metabolic changes in the host, and a shift in the composition, metabolism, and functionality of intestinal microbial communities. We conclude that HFrD alters the overall balance of the gut microbiota and induces an acceleration in EAC progression in a less pronounced manner than HFD.

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.