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BackgroundRetinoids are lipophilic isoprenoids composed of a cyclic group and a linear chain with a hydrophilic end group. These compounds include retinol, retinal, retinoic acid, retinyl esters, and various derivatives of these structures. Retinoids are used as cosmetic agents and effective pharmaceuticals for skin diseases. Retinal, an immediate precursor of retinoids, is derived by β-carotene 15,15'-mono(di)oxygenase (BCM(D)O) from β-carotene, which is synthesized from the isoprenoid building blocks isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). Retinoids are chemically unstable and biologically degraded via retinoic acid. Although extensive studies have been performed on the microbial production of carotenoids, retinoid production using microbial metabolic engineering has not been reported. Here, we report retinoid production using engineered Escherichia coli that express exogenous BCM(D)O and the mevalonate (MVA) pathway for the building blocks synthesis in combination with a two-phase culture system using a dodecane overlay.ResultsAmong the BCM(D)O tested in E. coli, the synthetic retinoid synthesis protein (SR), based on bacteriorhodopsin-related protein-like homolog (Blh) of the uncultured marine bacteria 66A03, showed the highest β-carotene cleavage activity with no residual intracellular β-carotene. By introducing the exogenous MVA pathway, 8.7 mg/L of retinal was produced, which is 4-fold higher production than that of augmenting the MEP pathway (dxs overexpression). There was a large gap between retinal production and β-carotene consumption using the exogenous MVA pathway; therefore, the retinal derivatives were analyzed. The derivatives, except for retinoic acid, that formed were identified, and the levels of retinal, retinol, and retinyl acetate were measured. Amounts as high as 95 mg/L retinoids were obtained from engineered E. coli DH5α harboring the synthetic SR gene and the exogenous MVA pathway in addition to dxs overexpression, which were cultured at 29°C for 72 hours with 2YT medium containing 2.0% (w/v) glycerol as the main carbon source. However, a significant level of intracellular degradation of the retinoids was also observed in the culture. To prevent degradation of the intracellular retinoids through in situ extraction from the cells, a two-phase culture system with dodecane was used. The highest level of retinoid production (136 mg/L) was obtained after 72 hours with 5 mL of dodecane overlaid on a 5 mL culture.ConclusionsIn this study, we successfully produced 136 mg/L retinoids, which were composed of 67 mg/L retinal, 54 mg/L retinol, and 15 mg/L retinyl acetate, using a two-phase culture system with dodecane, which produced 68-fold more retinoids than the initial level of production (2.2 mg/L). Our results demonstrate the potential use of E. coli as a promising microbial cell factory for retinoid production.

Background: The association of metabolic syndrome and its components with the risk of thyroid cancer is unclear. Thus, we conducted a large-scale, nationwide, population-based, cohort study to investigate this relationship. Methods: We studied 9,890,917 adults without thyroid cancer from the Korean National Health Insurance health checkup database from January 1 to December 31, 2009. Individuals with at least three of the following five components were diagnosed with metabolic syndrome: abdominal obesity, hypertriglyceridemia, low highdensity lipoprotein-cholesterol levels, elevated blood pressure, and hyperglycemia. Multivariate Cox proportional hazards models were used to estimate thyroid cancer risk. Results: During the average 7.2 years of follow-up, 77,133 thyroid cancer cases were newly identified. The thyroid cancer risk was higher in the metabolic syndrome group than in the nonmetabolic syndrome group (hazard ratio [HR] 1.15 [95% confidence interval, CI 1.13-1.17]). The association between metabolic syndrome and thyroid cancer risk was significant in the obese group (HR 1.10 [CI 1.07-1.13]) and not in the nonobese group (HR 1.002 [CI 0.98-1.03]). The effect of metabolic syndrome on the risk of thyroid cancer differs according to obesity ( p for interaction = 0.017). People with all five components of metabolic syndrome had a 39% higher risk than those without any components (HR 1.39 ). The higher risk of thyroid cancer in people with all five components was significant in the obese group ), but not in the nonobese group (HR 1.06 [CI 0.98-1.14]). There was a significant interaction between the number of metabolic syndrome components and obesity ( p for interaction <0.0001). For the combined effect of obesity and metabolic syndrome on the risk of thyroid cancer, obese men with metabolic syndrome had the highest risk of thyroid cancer compared with those without ), but obese women with metabolic syndrome did not. Conclusions: Metabolic syndrome was associated with an increased risk of thyroid cancer in the Korean general population. Metabolic syndrome had a more significant risk of thyroid cancer in the obese group. Metabolic syndrome and obesity were associated with a higher risk of thyroid cancer in men but not in women.

BackgroundIsoprene, a volatile C5 hydrocarbon, is an important platform chemical used in the manufacturing of synthetic rubber for tires and various other applications, such as elastomers and adhesives.ResultsIn this study, Escherichia coli MG1655 harboring Populus trichocarpa isoprene synthase (PtispS) and the exogenous mevalonate (MVA) pathway produced 80 mg/L isoprene. Codon optimization and optimal expression of the ispS gene via adjustment of the RBS strength and inducer concentration increased isoprene production to 199 and 337 mg/L, respectively. To augment expression of MVA pathway genes, the MVA pathway was cloned on a high-copy plasmid (pBR322 origin) with a strong promoter (Ptrc), which resulted in an additional increase in isoprene production up to 956 mg/L. To reduce the formation of byproducts derived from acetyl-CoA (an initial substrate of the MVA pathway), nine relevant genes were deleted to generate the E. coli AceCo strain (E. coli MG1655 ΔackA-pta, poxB, ldhA, dld, adhE, pps, and atoDA). The AceCo strain harboring the ispS gene and MVA pathway showed enhanced isoprene production of 1832 mg/L in flask culture with reduced accumulation of byproducts.ConclusionsWe achieved a 23-fold increase in isoprene production by codon optimization of PtispS, augmentation of the MVA pathway, and deletion of genes involved in byproduct formation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0612-6) contains supplementary material, which is available to authorized users.

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limits the further downscaling of Si-based electronic devices. 2D layered materials have attracted significant attention as post-Si nanoelectronic materials owing to their intriguing properties such as atomic thickness, having no dangling bond in a surface, high surface-to-volume ratio, and immunity to the short-channel effect. [1] Among the various 2D materials, 2H transition metal dichalcogenides (TMDCs), represented by MoS 2 and WSe 2 , are promising candidates for next-generation semiconductor materials in a post-Si era. They have suitable energy bandgaps and excellent electrical and optoelectronic properties that can overcome the fundamental limitations of graphene, which has zero energy bandgap. [2] TMDCs have the chemical structure of MX 2 , where M is a transition metal and X is a chalcogen atom, and they present a versatile platform with unique characteristics that depend on the combination of atoms. [3] In particular, WSe 2 exhibits ambipolar characteristics with high carrier mobilities (≈250 cm 2 V −1 •s for electron and 270 cm 2 V −1 •s for hole) and a bandgap that can be tuned according to the thickness (1.2 eV for monolayer and 1.7 eV for bulk). [4] It has been utilized in various electronic and optoelectronic applications, such as volatile and non-volatile memory, transistors, and photodetectors. [5][6][7][8][9] Despite the desirable characteristics of 2D TMDCs, the performance of intrinsic 2D TMDC-based electronic devices is still limited by low carrier concentrations and high contact resistance. [10][11][12] Impurity doping is a useful strategy to address these limitations. In conventional Si-based complementary metal-oxide-semiconductor (CMOS) technology, substitutional doping methods using ion implantation have been used to obtain electron-dominant and hole-dominant transport. [13,14] However, the ion implantation technique is inadequate for atomically thin semiconductor materials because it is extremely challenging to control the stopping ranges within a few nanometers. Ambipolar semiconductors which can exploit electrons and holes simultaneously in one channel are expected to simplify the complex ion implantation and subsequent rapid thermal processes. [15] Moreover, the use of ambipolar 2D semiconductor materials facilitates a reduction in footprint, providing opportunities for further miniaturization. If the majority carrier of an ambipolar 2D semiconductor can be effectively controlled, a high-performance multi-mode homojunction nanodevice Doping of van der Waals layered semiconductor materials is an essential technique to realize their full potential for implementation in nanoelectronics.Herein, defect-engineered and area-selective n-doping of ambipolar multi-layer WSe 2 are demonstrated via Ar plasma treatment. The contact regions of the WSe 2 are exposed to a mild Ar plasma treatment to induce Se vacancy, while the channel region is protected by a hexagonal boron nitride. The results are systematically analyzed using structural and optical characterization methods, and the origin of the...