A designed whole-cell biosensor for live diagnosis of gut inflammation through nitrate sensing

Microbes reprogrammed using advanced genetic circuits are envisaged as emerging living diagnostics for a wide range of diseases and play key roles in regulating gut microbiota to treat disease-associated symptoms in a non-invasive manner. Here, we developed a designer probiotic Escherichia coli that senses and responds to nitrate, a biomarker of gut inflammation. To this end, we first employed the NarX-NarL two-component regulatory system in E. coli to construct a nitrate-responsive genetic circuit. Next, we optimized the nitrate biosensor for the best performance using measures of sensitivity and specificity. We then introduced this genetic circuit into a probiotic E. coli Nissle 1917. We demonstrated that the designed biosensor can sense elevated nitrate levels during gut inflammation in mice with native gut microbiota. Moreover, using Boolean AND gate, we generated a genetically encoded biosensor for simultaneous sensing of the thiosulfate and nitrate biomarkers, thus increasing the tool's specificity for diagnosing gut inflammation. The nitrate-responsive genetic circuit will enable new approaches for non-invasive diagnostics of inflammation-associated diseases.

Tetrameric architecture of an active phenol-bound form of the AAA+ transcriptional regulator DmpR

The Pseudomonas putida phenol-responsive regulator DmpR is a bacterial enhancer binding protein (bEBP) from the AAA⁺ ATPase family. Even though it was discovered more than two decades ago and has been widely used for aromatic hydrocarbon sensing, the activation mechanism of DmpR has remained elusive. Here, we show that phenol-bound DmpR forms a tetramer composed of two head-to-head dimers in a head-to-tail arrangement. The DmpR-phenol complex exhibits altered conformations within the C-termini of the sensory domains and shows an asymmetric orientation and angle in its coiled-coil linkers. The structural changes within the phenol binding sites and the downstream ATPase domains suggest that the effector binding signal is propagated through the coiled-coil helixes. The tetrameric DmpR-phenol complex interacts with the σ⁵⁴ subunit of RNA polymerase in presence of an ATP analogue, indicating that DmpR-like bEBPs tetramers utilize a mechanistic mode distinct from that of hexameric AAA⁺ ATPases to activate σ⁵⁴-dependent transcription.

Sensitive and Rapid Phenotyping of Microbes With Soluble Methane Monooxygenase Using a Droplet-Based Assay

Methanotrophs with soluble methane monooxygenase (sMMO) show high potential for various ecological and biotechnological applications. Here, we developed a high throughput method to identify sMMO-producing microbes by integrating droplet microfluidics and a genetic circuit-based biosensor system. sMMO-producers and sensor cells were encapsulated in monodispersed droplets with benzene as the substrate and incubated for 5 h. The sensor cells were analyzed as the reporter for phenol-sensitive transcription activation of fluorescence. Various combinations of methanotrophs and biosensor cells were investigated to optimize the performance of our droplet-integrated transcriptional factor biosensor system. As a result, the conditions to ensure sMMO activity to convert the starting material, benzene, into phenol, were determined. The biosensor signals were sensitive and quantitative under optimal conditions, showing that phenol is metabolically stable within both cell species and accumulates in picoliter-sized droplets, and the biosensor cells are healthy enough to respond quantitatively to the phenol produced. These results show that our system would be useful for rapid evaluation of phenotypes of methanotrophs showing sMMO activity, while minimizing the necessity of time-consuming cultivation and enzyme preparation, which are required for conventional analysis of sMMO activity.

Hydrogel-Based Colorimetric Assay for Multiplexed MicroRNA Detection in a Microfluidic Device

Although microRNA (miRNA) expression levels provide important information regarding disease states owing to their unique dysregulation patterns in tissues, translation of miRNA diagnostics into point-of-care (POC) settings has been limited by practical challenges. Here, we developed a hydrogel-based microfluidic platform for colorimetric profiling of miRNAs, without the use of complex external equipment for fluidics and imaging. For sensitive and reliable measurement without the risk of sequence bias, we employed a gold deposition-based signal amplification scheme and dark-field imaging, and seamlessly integrated a previously developed miRNA assay scheme into this platform. The assay demonstrated a limit of detection of 260 fM, along with multiplexing of small panels of miRNAs in healthy and cancer samples. We anticipate this versatile platform to facilitate a broad range of POC profiling of miRNAs in cancer-associated dysregulation with high-confidence by exploiting the unique features of hydrogel substrate in an on-chip format and colorimetric analysis.

Discovery and Biochemical Characterization of a Methanol Dehydrogenase From Lysinibacillus xylanilyticus

Bioconversion of C1 chemicals such as methane and methanol into higher carbon-chain chemicals has been widely studied. Methanol oxidation catalyzed by methanol dehydrogenase (Mdh) is one of the key steps in methanol utilization in bacterial methylotrophy. In bacteria, few NAD⁺-dependent Mdhs have been reported that convert methanol to formaldehyde. In this study, an uncharacterized Mdh gene from Lysinibacillus xylanilyticus (Lxmdh) was cloned and expressed in Escherichia coli. The maximum alcohol oxidation activity of the recombinant enzyme was observed at pH 9.5 and 55°C in the presence of 10 mM Mg²⁺. To improve oxidation activity, rational approach-based, site-directed mutagenesis of 16 residues in the putative active site and NAD⁺-binding region was performed. The mutations S101V, T141S, and A164F improved the enzyme’s specific activity toward methanol compared to that of the wild-type enzyme. These mutants show a slightly higher turnover rate than that of wild-type, although their K_M values were increased compared to that of wild-type. Consequently, according the kinetic results, S101, T141, and A164 positions may related to the catalytic activity in the active site for methanol dehydrogenation. It should be further studied other mutant variants with high activity for methanol. In conclusion, we characterized a new Lxmdh and its variants that may be potentially useful for the development of synthetic methylotrophy in the future.

Effects of Alzheimer's disease and Lewy body disease on subcortical atrophy

BACKGROUND AND PURPOSE

Subcortical structures are affected by neurodegeneration in Alzheimer's disease (AD) and Lewy body disease (LBD). Although the co-occurrence of AD and LBD pathologies and their possible interaction have been reported, the effect of AD and LBD on subcortical structures remains unknown. The effects of AD and LBD on subcortical atrophy and their relationship with cognitive dysfunction were investigated.

METHODS

The cross-sectional study recruited 42 patients with pure AD related cognitive impairment (ADCI), 30 patients with pure LBD related cognitive impairment (LBCI), 58 patients with mixed ADCI and LBCI, and 29 normal subjects. A general linear model was used to compare subcortical volume and shape amongst the groups, to investigate the independent and interaction effects of ADCI and LBCI on subcortical shape and volume, and to analyze the relationship between subcortical volume and cognitive dysfunction in each group.

RESULTS

Alzheimer's disease related cognitive impairment and LBCI were independently associated with subcortical atrophies in the hippocampus and amygdala and in the hippocampus and putamen respectively, but their interaction effect was not significant. Compared to the control group, the pure LBCI group exhibited additional local atrophies in the amygdala, caudate and thalamus. Subcortical atrophies correlated differently with cognitive dysfunction according to the underlying causes of cognitive dysfunction.

CONCLUSIONS

The patterns of subcortical atrophies and their correlation with cognitive dysfunction differ according to the underlying AD, LBD or concomitant AD and LBD.

Moderate hearing loss is related with social frailty in a community-dwelling older adults: The Korean Frailty and Aging Cohort Study (KFACS)

OBJECTIVES

To determine whether hearing loss is associated with social frailty in older adults.

METHODS

Cross-sectional analysis of cohort study data. Hearing was measured using of Pure-tone audiometry. Hearing loss was determined based on the average of hearing thresholds at 0.5, 1, and 2 kHz in the ear that had better hearing. Social frailty was defined based on the summation of the following 5 social components (1. Neighborhood meeting attendance 2. Talking to friend(s) sometimes 3.Someone gives you love and affection 4. Living alone 5. Meeting someone every day). Participants who had no correspondence to the components were considered non-social frailty; those with 1-2 components were considered social prefrailty; and those having 3 or more components were considered social frailty.

RESULTS

The prevalence of non-social frailty, social prefrailty, social frailty was 27.6%, 60.7% and 11.7% respectively. Of the five questions, two components (Neighborhood meeting attendance and Presence of someone who shows love and affection to the participants) were associated with hearing loss (p < 0.001). Compared to non-social frailty, the odds ratio of social frailty for hearing loss was 2.24 (95% CI 1.48-3.38) after adjusting for age, residential area, economic status, smoking, depressive disorder and MMSE, and 2.17 (95% CI 1.43-3.30) after further adjustments with physical frailty.

CONCLUSION

Hearing loss was associated with social frailty even after controlling confounding factors even including physical frailty.

CRISPR interference-mediated gene regulation in Pseudomonas putida KT2440

Targeted gene regulation is indispensable for reprogramming a cellular network to modulate a microbial phenotype. Here, we adopted the type II CRISPR interference (CRISPRi) system for simple and efficient regulation of target genes in Pseudomonas putida KT2440. A single CRISPRi plasmid was generated to express a nuclease-deficient Cas9 gene and a designed single guide RNA, under control of l-rhamnose-inducible P_{rha BAD} and the constitutive Biobrick J23119 promoter respectively. Two target genes were selected to probe the CRISPRi-mediated gene regulation: exogenous green fluorescent protein on the multicopy plasmid and endogenous glpR on the P. putida KT2440 chromosome, encoding GlpR, a transcriptional regulator that represses expression of the glpFKRD gene cluster for glycerol utilization. The CRISPRi system successfully repressed the two target genes, as evidenced by a reduction in the fluorescence intensity and the lag phase of P. putida KT2440 cell growth on glycerol. Furthermore, CRISPRi-mediated repression of glpR improved both the cell growth and glycerol utilization, resulting in the enhanced production of mevalonate in an engineered P. putida KT2440 harbouring heterologous genes for the mevalonate pathway. CRISPRi is expected to become a robust tool to reprogram P. putida KT2440 for the development of microbial cell factories producing industrially valuable products.

A synthetic microbial biosensor for high-throughput screening of lactam biocatalysts

Biocatalytic cyclization is highly desirable for efficient synthesis of biologically derived chemical substances, such as the commodity chemicals ε-caprolactam and δ-valerolactam. To identify biocatalysts in lactam biosynthesis, we develop a caprolactam-detecting genetic enzyme screening system (CL-GESS). The Alcaligenes faecalis regulatory protein NitR is adopted for the highly specific detection of lactam compounds against lactam biosynthetic intermediates. We further systematically optimize the genetic components of the CL-GESS to enhance sensitivity, achieving 10-fold improvement. Using this highly sensitive GESS, we screen marine metagenomes and find an enzyme that cyclizes ω-amino fatty acids to lactam. Moreover, we determine the X-ray crystal structure and catalytic residues based on mutational analysis of the cyclase. The cyclase is also used as a helper enzyme to sense intracellular ω-amino fatty acids. We expect this simple and accurate biosensor to have wide-ranging applications in rapid screening of new lactam-synthesizing enzymes and metabolic engineering for lactam bio-production.

A Genetically Encoded Biosensor for Monitoring Isoprene Production in Engineered Escherichia coli

Isoprene is a valuable precursor for synthetic rubber and a signature product of terpenoid pathways. Here, we developed an isoprene biosensor by employing a TbuT transcriptional regulator of Ralstonia pickettii to express a fluorescent reporter gene in response to intracellular isoprene in engineered Escherichia coli. The TbuT regulator recognizes isoprene as its less-preferred effector molecule; thus, we amplified the reporter gene expression using a T7 RNA polymerase-mediated transcriptional cascade and iteratively tuned the promoter transcribing tbuT to improve the sensitivity for detecting isoprene. When the engineered E. coli cells expressed heterologous genes for isoprene biosynthesis, the intracellular isoprene was expelled and the tbuT transcription factor was subsequently activated, leading to gfp expression. The chromosomal isoprene biosensor showed a linear correlation between GFP fluorescence and intracellular isoprene concentration. Using this chromosomal isoprene biosensor, we successfully identified the highest isoprene producer among four different E. coli strains producing different amounts of isoprene. The isoprene biosensor presented here can enable high-throughput screening of isoprene synthases and metabolic pathways for efficient and sustainable production of bioisoprene in engineered microbes.

Calibration methods of X-ray imaging crystal spectrometer on KSTAR

The detailed calibration methods and procedure for the X-ray imaging crystal spectrometer (XICS) in the Korea Superconducting Tokamak Advanced Research device are investigated. A cross comparison from two different diagnostics including the XICS and charge exchange spectrometer is the best option, in particular, when both systems can be operated simultaneously.

Development of wavelength calibration techniques for high-resolution x-ray imaging crystal spectrometers on the EAST tokamak

Newly developed large-area pixelated two-dimensional detector and two-crystal assemblies were deployed for the first time on tokamaks to enable time-resolved Bragg-diffracted x-ray imaging with good framing rate and water-cooling capabilities for in-vacuum long-pulse operations. High-quality helium-like (He-like) and hydrogen-like (H-like) argon spectra have been observed simultaneously for the first time on a single detector for a wide range of plasma parameters to infer both ion temperature and rotation profiles and support studies on spontaneous rotation, impurity transport, and RF physics. Since tokamak plasmas rotate in both the poloidal (θ) and toroidal (ϕ) directions, a reliable wavelength calibration is needed to account for the correct Doppler shift as well as to compute the spectrometer's instrumental function. Ly_α lines emitted from Cd x-ray tubes are proposed to be used as "markers" to provide an in situ calibration of the EAST's X-ray imaging crystal spectrometer systems measuring He- and H-like argon spectra. The first lab test indicated that the X-ray tube can excite strong Ly_α lines at 15 kV voltage and 1 mA current when the crystal is shined for 10 min. Other indirect calibration methods using locked-mode discharge scenarios were also studied as complementary methods.

Imputation of faulty magnetic sensors with coupled Bayesian and Gaussian processes to reconstruct the magnetic equilibrium in real time

A Bayesian with Gaussian process-based numerical method to impute a few missing magnetic signals caused by impaired magnetic probes during tokamak operations is developed such that the real-time reconstruction of magnetic equilibria, whose performance strongly depends on the measured magnetic signals and their intactness, is affected minimally. Likelihood of the Bayesian model constructed with Maxwell's equations, specifically Gauss's law for magnetism and Ampère's law, results in an infinite number of solutions if two or more magnetic signals are missing. This undesirable characteristic of the Bayesian model is remediated by coupling the model with the Gaussian process. Our proposed numerical method infers nine non-consecutive missing magnetic signals correctly in less than 1 ms suitable for the real-time reconstruction of magnetic equilibria during tokamak operations.

Upgrade of X-ray crystal spectrometer for high temperature measurement using neon-like xenon lines on EAST

A two-crystal X-ray spectrometer system has been implemented in the EAST tokamak to simultaneously diagnose high- and low-temperature plasmas using He- and H-like argon spectra. But for future fusion devices like ITER and Chinese Fusion Engineering Test Reactor (CFETR), argon ions become fully stripped in the core and the intensity of the H-like lines will be significantly at high temperatures (T_e > 5 keV). With increasing auxiliary heating power on EAST, the core plasma temperature could also reach 5 keV and higher. In such conditions, the use of a xenon puff becomes an appropriate choice for both ion-temperature and flow-velocity measurements. A new two-crystal system using a quartz 110 crystal (2d = 4.913 Å) to view He-like argon lines and a quartz 011 crystal (2d = 6.686 Å) to view Ne-like xenon spectra has been deployed on a poloidal X-ray crystal spectrometer. While the He-like argon spectra will be used to measure the plasma temperature in the edge plasma region, the Ne-like xenon spectra will be used for measurement in the hot core. The new crystal arrangement allows a wide temperature measurement ranging from 0.5 to 10 keV or even higher, being the first tests for burning plasmas like ITER and CFETR. The preliminary result of lab-tests, Ne-like xenon lines measurement will be presented.

Development of Bacillus methanolicus methanol dehydrogenase with improved formaldehyde reduction activity

Methanol dehydrogenase (MDH), an NAD⁺-dependent oxidoreductase, reversibly converts formaldehyde to methanol. This activity is a key step for both toxic formaldehyde elimination and methanol production in bacterial methylotrophy. We mutated decameric Bacillus methanolicus MDH by directed evolution and screened mutants for increased formaldehyde reduction activity in Escherichia coli. The mutant with the highest formaldehyde reduction activity had three amino acid substitutions: F213V, F289L, and F356S. To identify the individual contributions of these residues to the increased reduction activity, the activities of mutant variants were evaluated. F213V/F289L and F213V/F289L/F356S showed 25.3- and 52.8-fold higher catalytic efficiency (k_cat/K_m) than wild type MDH, respectively. In addition, they converted 5.9- and 6.4-fold more formaldehyde to methanol in vitro than the wild type enzyme. Computational modelling revealed that the three substituted residues were located at MDH oligomerization interfaces, and may influence oligomerization stability: F213V aids in dimer formation, and F289L and F356S in decamer formation. The substitutions may stabilise oligomerization, thereby increasing the formaldehyde reduction activity of MDH.

Structural and functional analyses of the cellulase transcription regulator CelR

CelR is a transcriptional regulator that controls the expression of cellulases catalyzing cellulose hydrolysis. However, the structural mechanism of its regulation has remained unclear. Here, we report the first structure of CelR, in this case with cellobiose bound. CelR consists of a DNA-binding domain (DBD) and a regulatory domain (RD), and homodimerizes with each monomer bound to cellobiose. A hinge region (HR) in CelR connects the DBD with the RD, and Leu59 in the HR acts as a 'leucine lever' that transduces a transcriptional activation signal. Furthermore, an α4 helix mediates the ligand-binding signal for transcriptional activation. Tyr84 and Gln301 can potentially alter the ligand specificity of CelR. This study provides a pivotal step toward understanding transcription of the cellulases.

Molecular and biochemical characterization of a novel isoprene synthase from Metrosideros polymorpha

BACKGROUND

Isoprene is a five-carbon chemical that is an important starting material for the synthesis of rubber, elastomers, and medicines. Although many plants produce huge amounts of isoprene, it is very difficult to obtain isoprene directly from plants because of its high volatility and increasing environmental regulations. Over the last decade, microorganisms have emerged as a promising alternative host for efficient and sustainable bioisoprene production. Isoprene synthase (IspS) has received much attention for the conversion of isoprene from dimethylallyl diphosphate (DMAPP). Herein, we isolated a highly expressible novel IspS gene from Metrosideros polymorpha (MpIspS), which was cloned and expressed in Escherichia coli, using a plant cDNA library and characterized its molecular and biochemical properties.

RESULTS

The signal sequence deleted MpIspS was cloned and expressed in E. coli as a 65-kDa monomer. The maximal activity of the purified MpIspS was observed at pH 6.0 and 55 °C in the presence of 5 mM Mn²⁺. The K_m, k_cat, and k_cat/K_m for DMAPP as a substrate were 8.11 mM, 21 min^- 1, and 2.59 mM^- 1 min^- 1, respectively. MpIspS was expressed along with the exogenous mevalonate pathway to produce isoprene in E. coli. The engineered cells produced isoprene concentrations of up to 23.3 mg/L using glycerol as the main carbon source.

CONCLUSION

MpIspS was expressed in large amounts in E. coli, which led to increased enzymatic activity and resulted in isoprene production in vivo. These results demonstrate a new IspS enzyme that is useful as a key biocatalyst for bioisoprene production in engineered microbes.

Dual-graft adult living donor liver transplantation with ABO-incompatible graft: short-term and long-term outcomes

ABO-incompatible (ABOi) dual-graft (DG) adult living donor liver transplantation (ALDLT) is not commonly performed due to its inherently intricate surgical technique and immunological complexity. Therefore, data are lacking on the short- and long-term clinical outcomes of ABOi DG ALDLT. We performed a retrospective study by reviewing the medical records of patients who underwent ABOi DG ALDLT between 2008 and 2014. Additionally, computed tomography volumetric analysis was conducted to assess the graft regeneration rate. The mean age of a total of 28 recipients was 50.2 ± 8.5 years, and the mean model for end-stage liver disease score was 12.2 ± 4.6. The 1-, 3-, and 5-year patient survival rate was 96.4% during the mean follow-up period of 57.0 ± 22.4 months. The 1-, 3-, and 5-year graft survival rate was 96.4%, 94.2%, and 92.0%, respectively, and no significant differences were observed between ABO-compatible (ABOc) and ABOi grafts (P = .145). The biliary complication rate showed no significant difference (P = .195) between ABOc and ABOi grafts. Regeneration rates of ABOi grafts were not significantly different from those of ABOc grafts. DG ALDLT with ABOi and ABOc graft combination seems to be a feasible option for expanding the donor pool without additional donor risks.

EuroQol Visual Analogue Scale (EQ-VAS) as a Predicting Tool for Frailty in Older Korean Adults: The Korean Frailty an Aging Cohort Study (KFACS)

OBJECTIVES

This study was conducted to determine the cutoff value and efficacy of the EuroQol Visual Analogue Scale (EQ-VAS) for predicting frailty.

DESIGN

The EQ-VAS medians (Interquartile Range) were compared and analyzed against the FFI.

PARTICIPANTS

The subjects were 1471 older adults aged 70 to 84 years who had completed both EQ-VAS and Fried Frailty index (FFI) in the first baseline year (2016) of the Korean Frailty and Aging Cohort Study.

RESULTS

Of the 1471 subjects,600 were classified as robust, 716 as pre-frail, and 155 as frail. The median EQ-VAS scores were 80.00 (20.00) for robust, 75.00 (25.00) for pre-frail, and 60.00 (25.00) for frail subjects.The medians of all five components of the FFI, weight loss (70.00 vs. 80.00), grip strength (70.00 vs. 80.00), exhaustion (70.00 vs. 80.00), walking velocity (70.00 vs. 80.00), and physical activity (70.00 vs. 80.00), were lower in the abnormal groups. We tested the efficacy of EQ-VAS as a diagnostic tool to predict frailty, and the area under the curve of EQ-VAS was 0.71 withthe optimal cut-off value of 72.

CONCLUSION

EQ-VAS presented negative correlation with FFI, and the optimal cut off value for frailty was 72. These results suggest that EQ-VAS is a valuable tool for assessing frailty andmay be a good predictor of frailty in Korean elderly population.

Development of a novel cellulase biosensor that detects crystalline cellulose hydrolysis using a transcriptional regulator

Successful utilization of cellulose as renewable biomass depends on the development of economically feasible technologies, which can aid in enzymatic hydrolysis. In this study, we developed a whole-cell biosensor for detecting cellulolytic activity that relies on the recognition of cellobiose using the transcriptional factor CelR from Thermobifida fusca and transcriptional activation of its downstream gfp reporter gene. The fluorescence intensity of whole-cell biosensor, which was named as cellobiose-detectible genetic enzyme screening system (CBGESS), was directly proportional to the concentration of cellobiose. The strong fluorescence intensity of CBGESS demonstrated the ability to detect cellulolytic activity with two cellulosic substrates, carboxymethyl cellulose and p-nitrophenyl β-D-cellobioside in cellulase-expressing Escherichia coli. In addition, CBGESS easily sensed crystalline cellulolytic activity when commercial Celluclast 1.5L was dropped on an Avicel plate. Therefore, CBGESS is a powerful tool for detecting cellulolytic activity with high sensitivity in the presence of soluble or insoluble cellulosic substrates. CBGESS may be further applied to excavate novel cellulases or microbes from both genetic libraries and various environments.

CRISPR interference-guided multiplex repression of endogenous competing pathway genes for redirecting metabolic flux in Escherichia coli

BACKGROUND

Multiplex control of metabolic pathway genes is essential for maximizing product titers and conversion yields of fuels, chemicals, and pharmaceuticals in metabolic engineering. To achieve this goal, artificial transcriptional regulators, such as clustered regularly interspaced short palindromic repeats (CRISPR) interference (CRISPRi), have been developed to specifically repress genes of interest.

RESULTS

In this study, we deployed a tunable CRISPRi system for multiplex repression of competing pathway genes and, thus, directed carbon flux toward production of molecules of interest in Escherichia coli. The tunable CRISPRi system with an array of sgRNAs successfully repressed four endogenous genes (pta, frdA, ldhA, and adhE) individually and in double, triple, or quadruple combination that are involved in the formation of byproducts (acetate, succinate, lactate, and ethanol) and the consumption of NADH in E. coli. Single-target CRISPRi effectively reduced the amount of each byproduct and, interestingly, pta repression also decreased ethanol production (41%), whereas ldhA repression increased ethanol production (197%). CRISPRi-mediated multiplex repression of competing pathway genes also resulted in simultaneous reductions of acetate, succinate, lactate, and ethanol production in E. coli. Among 15 conditions repressing byproduct-formation genes, we chose the quadruple-target CRISPRi condition to produce n-butanol in E. coli as a case study. When heterologous n-butanol-pathway enzymes were introduced into E. coli simultaneously repressing the expression of the pta, frdA, ldhA, and adhE genes via CRISPRi, n-butanol yield and productivity increased up to 5.4- and 3.2-fold, respectively.

CONCLUSIONS

We demonstrated the tunable CRISPRi system to be a robust platform for multiplex modulation of endogenous gene expression that can be used to enhance biosynthetic pathway productivity, with n-butanol as the test case. CRISPRi applications potentially enable the development of microbial "smart cell" factories capable of producing other industrially valuable products.

Living Donor Liver Transplantation for Patients Older Than Age 70 Years: A Single-Center Experience

Over the past two decades, the age of liver transplantation (LT) recipients has been increasing. We reviewed our experience with LT for patients aged ≥70 years (range: 70-78 years) and investigated the feasibility of performing LT, especially living donor LT (LDLT), for older patients. We retrospectively reviewed the medical records of 25 patients (15 LDLT recipients, 10 deceased donor LT recipients) aged ≥70 years who underwent LT from January 2000 to April 2016. Their perioperative morbidity rate was 28.0%, and the in-hospital mortality rate was 16.0%; these results were comparable to those of matched patients in their 60s (n = 73; morbidity, p = 0.726; mortality, p = 0.816). For patients in their 70s, the 1- and 5-year patient survival rates were 84.0% and 69.8%, and the 1- and 5-year graft survival rates were 83.5% and 75.1%, respectively. Comparisons of patient and graft survival rates between matched patients in their 60s and 70s showed no statistically significant differences (patient survival, p = 0.372; graft survival, p = 0.183). Our experience suggests that patients aged ≥70 years should not be excluded from LT, or even LDLT, based solely on age and implies that careful selection of recipients and donors as well as meticulous surgical technique are necessary for successful results.

Efficient Transcriptional Gene Repression by Type V-A CRISPR-Cpf1 from Eubacterium eligens

Clustered regularly interspaced short palindromic repeats interference (CRISPRi) is an emerging technology for artificial gene regulation. Type II CRISPR-Cas endonuclease Cas9 is the most widely used protein for gene regulation with CRISPRi. Here, we present type V-A CRISPR-Cas endonuclease Cpf1-based CRISPRi. We constructed an l-rhamnose-inducible CRISPRi system with DNase-deactivated Cpf1 from Eubacterium eligens (EedCpf1) and compared its performance with catalytically deactivated Cas9 from Streptococcus pyogenes (SpdCas9). In contrast to SpdCas9, EedCpf1 showed stronger gene repression when it was targeted to the template strand than when it was targeted to the nontemplate strand of the 5' untranslated region or coding DNA sequences. EedCpf1 exhibited no strand bias when targeted to the promoter, and preferentially used the 5'-TTTV-3' (V = A, G, or C) protospacer adjacent motif. Multiplex repression of the EedCpf1-based CRISPRi system was demonstrated using episomal and chromosomal gene targets. Our findings will guide an efficient EedCpf1-mediated CRISPRi genetic control.