Mass production and characterization of an endoglucanase from Coleoptera insect (Monochamus saltuarius) in yeast Kluyveromyces lactis.

To harness the diverse industrial applications of cellulase, including its use in the food, pulp, textile, agriculture, and biofuel sectors, this study focused on the high-yield production of a bioactive insect-derived endoglucanase, Monochamus saltuarius GH Family 5 (MsGHF5). MsGHF5 was introduced into the genome of Kluyveromyces lactis to maintain expression stability, and mass production of the enzyme was induced using fed-batch fermentation. After 40 h of cultivation, recombinant MsGHF5 was successfully produced in the culture broth, with a yield of 29,000 U/L, upon galactose induction. The optimal conditions for the activity of purified MsGHF5 were determined to be a pH of 5 and a temperature of 35 °C, with the presence of ferrous ions enhancing the enzymatic activity by up to 1.5-fold. Notably, the activity of MsGHF5 produced in K. lactis was significantly higher than that produced in Escherichia coli, suggesting that glycosylation is crucial for the functional performance of the enzyme. This study highlights the potential use of K. lactis as a host for the production of bioactive MsGHF5, thus paving the way for its application in various industrial sectors.

Dilute acid-assisted microbubbles-mediated ozonolysis of Eucheuma denticulatum phycocolloid for biobased L-lactic acid production.

Biobased L-lactic acid (L-LA) appeals to industries; however, existing technologies are plagued by limited productivity and high energy consumption. This study established an integrated process for producing macroalgae-based L-LA from Eucheuma denticulatum phycocolloid (EDP). Dilute acid-assisted microbubbles-mediated ozonolysis (DAMMO) was selected for the ozonolysis of EDP to optimize D-galactose recovery. Through single-factor optimization of DAMMO treatment, a maximum D-galactose recovery efficiency (59.10 %) was achieved using 0.15 M H2SO4 at 80 °C for 75 min. Fermentation with 3 % (w/v) mixed microbial cells (Bacillus coagulans ATCC 7050 and Lactobacillus acidophilus-14) and fermented residues achieved a 97.67 % L-LA yield. Additionally, this culture approach was further evaluated in repeated-batch fermentation and showed an average L-LA yield of 93.30 %, providing a feasible concept for macroalgae-based L-LA production.

Exploring the impact of magnetic fields on biomass production efficiency under aerobic and anaerobic batch fermentation of Saccharomyces cerevisiae.

In this work, the effect of moderate electromagnetic fields (2.5, 10, and 15 mT) was studied using an immersed coil inserted directly into a bioreactor on batch cultivation of yeast under both aerobic and anaerobic conditions. Throughout the cultivation, parameters, including CO2 levels, O2 saturation, nitrogen consumption, glucose uptake, ethanol production, and yeast growth (using OD 600 measurements at 1-h intervals), were analysed. The results showed that 10 and 15 mT magnetic fields not only statistically significantly boosted and sped up biomass production (by 38-70%), but also accelerated overall metabolism, accelerating glucose, oxygen, and nitrogen consumption, by 1-2 h. The carbon balance analysis revealed an acceleration in ethanol and glycerol production, albeit with final concentrations by 22-28% lower, with a more pronounced effect in aerobic cultivation. These findings suggest that magnetic fields shift the metabolic balance toward biomass formation rather than ethanol production, showcasing their potential to modulate yeast metabolism. Considering coil heating, opting for the 10 mT magnetic field is preferable due to its lower heat generation. In these terms, we propose that magnetic field can be used as novel tool to increase biomass yield and accelerate yeast metabolism.

Efficient production of polyhydroxybutyrate using lignocellulosic biomass derived from oil palm trunks by the inhibitor-tolerant strain Burkholderia ambifaria E5-3.

Lignocellulosic biomass is a valuable, renewable substrate for the synthesis of polyhydroxybutyrate (PHB), an ecofriendly biopolymer. In this study, bacterial strain E5-3 was isolated from soil in Japan; it was identified as Burkholderia ambifaria strain E5-3 by 16 S rRNA gene sequencing. The strain showed optimal growth at 37 °C with an initial pH of 9. It demonstrated diverse metabolic ability, processing a broad range of carbon substrates, including xylose, glucose, sucrose, glycerol, cellobiose, and, notably, palm oil. Palm oil induced the highest cellular growth, with a PHB content of 65% wt. The strain exhibited inherent tolerance to potential fermentation inhibitors derived from lignocellulosic hydrolysate, withstanding 3 g/L 5-hydroxymethylfurfural and 1.25 g/L acetic acid. Employing a fed-batch fermentation strategy with a combination of glucose, xylose, and cellobiose resulted in PHB production 2.7-times that in traditional batch fermentation. The use of oil palm trunk hydrolysate, without inhibitor pretreatment, in a fed-batch fermentation setup led to significant cell growth with a PHB content of 45% wt, equivalent to 10 g/L. The physicochemical attributes of xylose-derived PHB produced by strain E5-3 included a molecular weight of 722 kDa, a number-average molecular weight of 191 kDa, and a polydispersity index of 3.78. The amorphous structure of this PHB displayed a glass transition temperature of 4.59 °C, while its crystalline counterpart had a melting point of 171.03 °C. This research highlights the potential of lignocellulosic feedstocks, especially oil palm trunk hydrolysate, for PHB production through fed-batch fermentation by B. ambifaria strain E5-3, which has high inhibitor tolerance.

Enhancing Phycocyanobilin Production Efficiency in Engineered Corynebacterium glutamicum: Strategies and Potential Application.

Phycocyanobilin, an algae-originated light-harvesting pigment known for its antioxidant properties, has gained attention as it plays important roles in the food and medication industries and has surged in demand owing to its low-yield extraction from natural resources. In this study, engineered Corynebacterium glutamicum was developed to achieve high PCB production, and three strategies were proposed: reinforcement of the heme biosynthesis pathway with the introduction of two PCB-related enzymes, strengthening of the pentose phosphate pathway to generate an efficient cycle of NADPH, and fed-batch fermentation to maximize PCB production. Each approach increased PCB synthesis, and the final engineered strain successfully produced 78.19 mg/L in a flask and 259.63 mg/L in a 5 L bioreactor, representing the highest bacterial production of PCB reported to date, to our knowledge. The strategies applied in this study will be useful for the synthesis of PCB derivatives and can be applied in the food and pharmaceutical industries.

Optimization of fermentation conditions for the production of γ-aminobutyric acid by Lactobacillus hilgardii GZ2 from traditional Chinese fermented beverage system.

γ-Aminobutyric acid (GABA) is a crucial neurotransmitter with wide application prospects. In this study, we focused on a GABA-producing strain from a traditional Chinese fermented beverage system. Among the six isolates, Lactobacillus hilgardii GZ2 exhibited the greatest ability to produce GABA in the traditional Chinese fermented beverage system. To increase GABA production, we optimized carbon sources, nitrogen sources, temperature, pH, and monosodium glutamate and glucose concentrations and conducted fed-batch fermentation. The best carbon and nitrogen sources for GABA production and cell growth were glucose, yeast extract and tryptone. Gradual increases in GABA were observed as the glucose and monosodium glutamate concentrations increased from 10 g/L to 50 g/L. During fed-batch fermentation, lactic acid was used to maintain the pH at 5.56, and after feeding with 0.03 g/mL glucose and 0.4 g/mL sodium glutamate for 72 h, the GABA yield reached 239 g/L. This novel high-GABA-producing strain holds great potential for the industrial production of GABA, as well as the development of health-promoting functional foods and medical fields.

Eggshell waste bioprocessing for sustainable acid phosphatase production and minimizing environmental hazards.

BACKGROUND: The Environmental Protection Agency has listed eggshell waste as the 15th most significant food industry pollution hazard. Using eggshell waste as a renewable energy source has been a hot topic recently. Therefore, finding a sustainable solution for the recycling and valorization of eggshell waste by investigating its potential to produce acid phosphatase (ACP) and organic acids by the newly-discovered B. sonorensis was the target of the current investigation. RESULTS: Drawing on both molecular and morphological characterizations, the most potent ACP-producing B. sonorensis strain ACP2, was identified as a local bacterial strain obtained from the effluent of the paper and pulp industries. The use of consecutive statistical experimental approaches of Plackett-Burman Design (PBD) and Orthogonal Central Composite Design (OCCD), followed by pH-uncontrolled cultivation conditions in a 7 L bench-top bioreactor, revealed an innovative medium formulation that substantially improved ACP production, reaching 216 U L-1 with an ACP yield coefficient Yp/x of 18.2 and a specific growth rate (µ) of 0.1 h-1. The metals Ag+, Sn+, and Cr+ were the most efficiently released from eggshells during the solubilization process by B. sonorensis. The uncontrolled pH culture condition is the most suitable and favoured setting for improving ACP and organic acids production. Quantitative and qualitative analyses of the produced organic acids were carried out using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Lactic acid, citric acid, and hydroxybenzoic acid isomer were the most common organic acids produced throughout the cultivation process. The findings of TGA, DSC, SEM, EDS, FTIR, and XRD analysis emphasize the significant influence of organic acids and ACP activity on the solubilization of eggshell particles. CONCLUSIONS: This study emphasized robust microbial engineering approaches for the large-scale production of a newly discovered acid phosphatase, accompanied by organic acids production from B. sonorensis. The biovalorization of the eggshell waste and the production of cost-effective ACP and organic acids were integrated into the current study, and this was done through the implementation of a unique and innovative medium formulation design for eggshell waste management, as well as scaling up ACP production on a bench-top scale.

Enhancing astaxanthin biosynthesis and pathway expansion towards glycosylated C40 carotenoids by Corynebacterium glutamicum.

Astaxanthin, a versatile C40 carotenoid prized for its applications in food, cosmetics, and health, is a bright red pigment with powerful antioxidant properties. To enhance astaxanthin production in Corynebacterium glutamicum, we employed rational pathway engineering strategies, focused on improving precursor availability and optimizing terminal oxy-functionalized C40 carotenoid biosynthesis. Our efforts resulted in an increased astaxanthin precursor supply with 1.5-fold higher ß-carotene production with strain BETA6 (18 mg g-1 CDW). Further advancements in astaxanthin production were made by fine-tuning the expression of the ß-carotene hydroxylase gene crtZ and ß-carotene ketolase gene crtW, yielding a nearly fivefold increase in astaxanthin (strain ASTA**), with astaxanthin constituting 72% of total carotenoids. ASTA** was successfully transferred to a 2 L fed-batch fermentation with an enhanced titer of 103 mg L-1 astaxanthin with a volumetric productivity of 1.5 mg L-1 h-1. Based on this strain a pathway expansion was achieved towards glycosylated C40 carotenoids under heterologous expression of the glycosyltransferase gene crtX. To the best of our knowledge, this is the first time astaxanthin-ß-D-diglucoside was produced with C. glutamicum achieving high titers of microbial C40 glucosides of 39 mg L-1. This study showcases the potential of pathway engineering to unlock novel C40 carotenoid variants for diverse industrial applications.

Multivariate modular metabolic engineering and medium optimization for vitamin B12 production by Escherichia coli.

Vitamin B12 is a complex compound synthesized by microorganisms. The industrial production of vitamin B12 relies on specific microbial fermentation processes. E. coli has been utilized as a host for the de novo biosynthesis of vitamin B12, incorporating approximately 30 heterologous genes. However, a metabolic imbalance in the intricate pathway significantly limits vitamin B12 production. In this study, we employed multivariate modular metabolic engineering to enhance vitamin B12 production in E. coli by manipulating two modules comprising a total of 10 genes within the vitamin B12 biosynthetic pathway. These two modules were integrated into the chromosome of a chassis cell, regulated by T7, J23119, and J23106 promoters to achieve combinatorial pathway optimization. The highest vitamin B12 titer was attained by engineering the two modules controlled by J23119 and T7 promoters. The inclusion of yeast powder to the fermentation medium increased the vitamin B12 titer to 1.52 mg/L. This enhancement was attributed to the effect of yeast powder on elevating the oxygen transfer rate and augmenting the strain's isopropyl-ß-d-1-thiogalactopyranoside (IPTG) tolerance. Ultimately, vitamin B12 titer of 2.89 mg/L was achieved through scaled-up fermentation in a 5-liter fermenter. The strategies reported herein will expedite the development of industry-scale vitamin B12 production utilizing E. coli.

Heterotrophic and autotrophic production of L-isoleucine and L-valine by engineered Cupriavidus necator H16.

Advancement in commodity chemical production from carbon dioxide (CO2) offers a promising path towards sustainable development goal. Cupriavidus necator is an ideal host to convert CO2 into high-value chemicals, thereby achieving this target. Here, C. necator was engineered for heterotrophic and autotrophic production of L-isoleucine and L-valine. Citramalate synthase was introduced to simplify isoleucine synthesis pathway. Blocking poly-hydroxybutyrate biosynthesis resulted in significant accumulation of isoleucine and valine. Besides, strategies like key enzymes screening and overexpressing, reducing power balancing and feedback inhibition removing were applied in strain modification. Finally, the maximum isoleucine and valine titers of the best isoleucine-producing and valine-producing strains reached 857 and 972 mg/L, respectively, in fed-batch fermentation using glucose as substrate, and 105 and 319 mg/L, respectively, in autotrophic fermentation using CO2 as substrate. This study provides a feasible solution for developing C. necator as a microbial factory to produce amino acids from CO2.

High Cell Density Cultivation Combined with high Specific Enzyme Activity: Cultivation Protocol for the Production of an Amine Transaminase from Bacillus megaterium in E. coli.

High cell density cultivation is an established method for the production of various industrially important products such as recombinant proteins. However, these protocols are not always suitable for biocatalytic processes as the focus often lies on biomass production rather than high specific activities of the enzyme inside the cells. In contrast, a range of shake flask protocols are well known with high specific activities but rather low cell densities. To overcome this gap, we established a tailor-made fed-batch protocol combining both aspects: high cell density and high specific activities of heterologously produced enzyme. Using the example of an industrially relevant amine transaminase from Bacillus megaterium, we describe a strategy to optimize the cultivation yield based on the feed rate, IPTG concentration, and post-induction temperature. By adjusting these key parameters, we were able to increase the specific activity by 2.6-fold and the wet cell weight by even 17-fold compared to shake flasks. Finally, we were able to verify our established protocol by transferring it to another experimenter. With that, our optimization strategy can serve as a template for the production of high titers of heterologously produced, active enzymes and might enable the availability of these catalysts for upscaling biocatalytic processes.

Fault diagnosis based on counterfactual inference for the batch fermentation process.

Fault diagnosis plays a pivotal role in identifying the root causes of a fault. Current fault diagnosis methods encounter the shortcomings being unable to assess the fault amplitude or having low efficiency for batch fermentation process. In order to solve the above problems, this paper proposes a fault detection model named convolutional neural network based on variational autoencoder (CNN-VAE) and a fault diagnosis based on counterfactual inference (FDCI). To begin with, quality-related process variables are selected using mutual information (MI). Next, a two-dimensional moving window is used to obtain input sequences from the process data. Then, two statistics from the latent and residual domains of the CNN-VAE model are constructed for fault detection. Additionally, once a fault occurs, FDCI is used to locate the root cause of a fault. Finally, a simulation process and a real-world L. plantarum batch fermentation process are provided to demonstrate the effectiveness of the proposed approache.

[Optimization of the fermentative production of L-methionine by engineered Escherichia coli].

As the only essential amino acid containing elemental sulphur, L-methionine has important physiological and biochemical functions in living organisms. However, the fermentative production of L-methionine has not met the requirements of industrial production because of its low production level. In this paper, the fermentation process of an efficient L-methionine producing strain E. coli W3110ΔIJAHFEBC trc-fliY trc-malY/PAM glyA-22 metF constructed previously was systematically optimized. Based on the optimal initial glucose concentration, the effects of different fed-batch fermentation processes, including DO-Stat, pH-Stat, controlling residual sugar control at different level and feeding glucose with constant rate, on L-methionine fermentation were studied. It was found that the control of glucose concentration greatly affected the fermentation process. Subsequently, an optimal fed-batch fermentation process was developed, where the L-methionine titer was increased to 31.71 g/L, the highest yield reported to date, while the fermentation time was shortened to 68 h. Meanwhile, a fermentation kinetics model under the optimal fed-batch fermentation conditions was established, which fitted well with the biosynthesis process of L-methionine. This study may facilitate further development of the fermentative production of L-methionine.

Construction and Regulation of the Abscisic Acid Biosynthesis Pathway in Yarrowia lipolytica.

Abscisic acid (ABA) is an important plant hormone with a variety of physiological functions such as regulating plant growth and helping plants to resist an adverse growth environment. However, at present, the ABA yield of heterologous biosynthesis by metabolic engineering is still low for industrial production. Therefore, five Botrytis cinerea genes (bcaba1, bcaba2, bcaba3, bcaba4, and bccpr1) related to ABA biosynthesis were expressed in Yarrowia lipolytica PO1h; its ABA production was 24.33 mg/L. By increasing the copy number of IDI and ERG12S, ERG20YMT, and bcaba3, bcaba1 genes, the yield of ABA was increased to 54.51 mg/L. By locating HMG-CoA reductase and HMG-CoA synthase in mitochondria, acetyl-CoA in mitochondria was converted into mevalonate; this increased the ABA yield to 102.12 mg/L. Finally, in the fed-batch fermentation process with the addition of dodecane, the ABA yield was up to 1212.57 mg/L, which is the highest yield of heterologous production of ABA by metabolic engineering.

Food additives impair gut microbiota from healthy individuals and IBD patients in a colonic in vitro fermentation model.

Intestinal fibrosis is a long-term complication of inflammatory bowel diseases (IBD). Changes in microbial populations have been linked with the onset of fibrosis and some food additives are known to promote intestinal inflammation facilitating fibrosis induction. In this study, we investigated how polysorbate 80, sucralose, titanium dioxide, sodium nitrite and maltodextrin affect the gut microbiota and the metabolic activity in healthy and IBD donors (patients in remission and with a flare of IBD). The Simulator of the Human Intestinal Microbial Ecosystem (SHIME®) with a static (batch) configuration was used to evaluate the effects of food additives on the human intestinal microbiota. Polysorbate 80 and sucralose decreased butyrate-producing bacteria such as Roseburia and Faecalibacterium prausnitzii. Both compounds, also increased bacterial species positively correlated with intestinal inflammation and fibrosis (i.e.: Enterococcus, Veillonella and Mucispirillum schaedleri), especially in donors in remission of IBD. Additionally, polysorbate 80 induced a lower activity of the aryl hydrocarbon receptor (AhR) in the three groups of donors, which can affect the intestinal homeostasis. Maltodextrin, despite increasing short-chain fatty acids production, promoted the growth of Ruminococcus genus, correlated with higher risk of fibrosis, and decreased Oscillospira which is negatively associated with fibrosis. Our findings unveil crucial insights into the potential deleterious effects of polysorbate 80, sucralose and maltodextrin on human gut microbiota in healthy and, to a greater extent, in IBD patients.

Systematic Engineering of Escherichia coli for Efficient Production of Pseudouridine from Glucose and Uracil.

In this study, we proposed a biological approach to efficiently produce pseudouridine (Ψ) from glucose and uracil in vivo using engineered Escherichia coli. By screening host strains and core enzymes, E. coli MG1655 overexpressing Ψ monophosphate (ΨMP) glycosidase and ΨMP phosphatase was obtained, which displayed the highest Ψ concentration. Then, optimization of the RBS sequences, enhancement of ribose 5-phosphate supply in the cells, and overexpression of the membrane transport protein UraA were investigated. Finally, fed-batch fermentation of Ψ in a 5 L fermentor can reach 27.5 g/L with a yield of 89.2 mol % toward uracil and 25.6 mol % toward glucose within 48 h, both of which are the highest to date. In addition, the Ψ product with a high purity of 99.8% can be purified from the fermentation broth after crystallization. This work provides an efficient and environmentally friendly protocol for allowing for the possibility of Ψ bioproduction on an industrial scale.

Efficient Biosynthesis of Difucosyllactose via De Novo GDP-l-Fucose Pathway in Metabolically Engineered Escherichia coli.

Difucosyllactose (DFL) is an important component of human milk oligosaccharides (HMOs) and has significant benefits for the growth and development of infants. So far, a few microbial cell factories have been constructed for the production of DFL, which still have problems of low production and high cost. Herein, a high-level de novo pathway DFL-producing strain was constructed by multistep optimization strategies in Escherichia coli BL21star(DE3). We first efficiently synthesized the intermediate 2'-fucosyllactose (2'-FL) in E. coli BL21star(DE3) by the advisable stepwise strategy. The truncated α-1,3/4-fucosyltransferase (Hp3/4FT) was then introduced into the engineered strain to achieve de novo biosynthesis of DFL. ATP-dependent protease (Lon) and GDP-mannose hydrolase (NudK) were deleted, and mannose-6-phosphate isomerase (ManA) was overexpressed to improve GDP-l-fucose accumulation. The regulator RcsA was overexpressed to fine-tune the expression level of pathway genes, thereby increasing the synthesis of DFL. The final strain produced 6.19 g/L of DFL in the shake flask and 33.45 g/L of DFL in the 5 L fermenter, which were the highest reported titers so far. This study provides a more economical, sustainable, and effective strategy to produce the fucosylated human milk oligosaccharides (HMOs).

M-Batches to Simulate Luminal and Mucosal Human Gut Microbial Ecosystems: A Case Study of the Effects of Coffee and Green Tea.

Gastrointestinal simulations in vitro have only limited approaches to analyze the microbial communities inhabiting the mucosal compartment. Understanding and differentiating gut microbial ecosystems is crucial for a more comprehensive and accurate representation of the gut microbiome and its interactions with the host. Herein is suggested, in a short-term and static set-up (named "M-batches"), the analysis of mucosal and luminal populations of inhabitants of the human colon. After varying several parameters, such as the fermentation volume and the fecal inoculum (single or pool), only minor differences in microbial composition and metabolic production were identified. However, the pool created with feces from five donors and cultivated in a smaller volume (300 mL) seemed to provide a more stable luminal ecosystem. The study of commercially available coffee and green tea in the M-batches suggested some positive effects of these worldwide known beverages, including the increase in butyrate-producing bacteria and lactobacilli populations. We hope that this novel strategy can contribute to future advances in the study of intestinal ecosystems and host-microbe relationships and help elucidate roles of the microbiome in health and disease.

Metabolic control analysis enabled the improvement of the L-cysteine production process with Escherichia coli.

L-cysteine is an amino acid with relevance to the pharmaceutical, food, feed, and cosmetic industry. The environmental and societal impact of its chemical production has led to the development of more sustainable fermentative L-cysteine production processes with engineered E. coli based on glucose and thiosulfate as sulphur source. Still, most of the published processes show low yields. For the identification of further metabolic engineering targets, engineered E. coli cells were withdrawn from a fed-batch production process, followed by in vivo metabolic control analysis (MCA) based on the data of short-term perturbation experiments, metabolomics (LC-MS), and thermodynamic flux analysis (TFA). In vivo MCA indicated that the activities of the L-cysteine synthases of the cells withdrawn from the production process might be limiting, and we hypothesised that the L-cysteine precursor O-acetylserine (OAS) might be exported from the cells faster than it took to transform OAS into L-cysteine. By increasing the expression of the L-cysteine synthases, either sulfocysteine synthase or L-cysteine synthase, which transform OAS into L-cysteine, an improvement of up to 70% in specific L-cysteine productivity and up to 47% in the final L-cysteine concentration was achieved in standardised fed-batch processes thereby increasing the yield on glucose by more than 85 to 9.2% (w/w). KEY POINTS: • Metabolic control analysis was applied to analyse L-cysteine production with E. coli • OAS export was faster than its transformation to L-cysteine • Overexpression of L-cysteine synthases improved L-cysteine productivity and yield.

Construction of an engineered Escherichia coli for effective synthesis of 2'-fucosyllactose via the salvage pathway.

2'-Fucosyllactose (2'-FL) is one of the important functional oligosaccharides in breast milk. So far, few attempts on biosynthesis of 2'-FL by the salvage pathway have been reported. Herein, the salvage pathway enzyme genes were introduced into the E. coli BL21star(DE3) for synthesis of 2'-FL. The 2'-FL titer increased from 1.56 to 2.13 g/L by deleting several endogenous genes on competitive pathways. The α-1,2-fucosyltransferase (WbgL) was selected, and improved the 2'-FL titer to 2.88 g/L. Additionally, the expression level of pathway enzyme genes was tuned through optimizing the plasmid copy number. Furthermore, the spatial distribution of WbgL was enhanced by fusing with the MinD C-tag. After optimizing the fermentation conditions, the 2'-FL titer reached to 7.13 g/L. The final strain produced 59.22 g/L of 2'-FL with 95% molar conversion rate of lactose and 92% molar conversion rate of fucose in a 5 L fermenter. These findings will contribute to construct a highly efficient microbial cell factory to produce 2'-FL or other HMOs.