Metabolic engineering of Escherichia coli for efficient production of L-alanyl-L-glutamine.

BACKGROUND: L-Alanyl-L-glutamine (AQ) is a functional dipeptide with high water solubility, good thermal stability and high bioavailability. It is widely used in clinical treatment, post-operative rehabilitation, sports health care and other fields. AQ is mainly produced via chemical synthesis which is complicated, time-consuming, labor-intensive, and have a low yield accompanied with the generation of by-products. It is therefore highly desirable to develop an efficient biotechnological process for the industrial production of AQ. RESULTS: A metabolically engineered E. coli strain for AQ production was developed by over-expressing L-amino acid α-ligase (BacD) from Bacillus subtilis, and inactivating the peptidases PepA, PepB, PepD, and PepN, as well as the dipeptide transport system Dpp. In order to use the more readily available substrate glutamic acid, a module for glutamine synthesis from glutamic acid was constructed by introducing glutamine synthetase (GlnA). Additionally, we knocked out glsA-glsB to block the first step in glutamine metabolism, and glnE-glnB involved in the ATP-dependent addition of AMP/UMP to a subunit of glutamine synthetase, which resulted in increased glutamine supply. Then the glutamine synthesis module was combined with the AQ synthesis module to develop the engineered strain that uses glutamic acid and alanine for AQ production. The expression of BacD and GlnA was further balanced to improve AQ production. Using the final engineered strain p15/AQ10 as a whole-cell biocatalyst, 71.7 mM AQ was produced with a productivity of 3.98 mM/h and conversion rate of 71.7%. CONCLUSION: A metabolically engineered strain for AQ production was successfully developed via inactivation of peptidases, screening of BacD, introduction of glutamine synthesis module, and balancing the glutamine and AQ synthesis modules to improve the yield of AQ. This work provides a microbial cell factory for efficient production of AQ with industrial potential.

Plantactinospora solaniradicis sp. nov., a novel actinomycete isolated from the root of a tomato plant (Solanum lycopersicum L.).

A Gram-positive, non-motile actinomycete, designated strain NEAU-FJL1T, was isolated from tomato root (Solanum lycopersicum L.) collected from Harbin, Heilongjiang province, north China. The strain formed single spores with smooth surfaces from substrate mycelia. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain NEAU-FJL1T should be affiliated with the genus Plantactinospora and forms a distinct branch with its close neighbour Plantactinospora soyae NEAU-gxj3T (99.2% sequence similarity). The cell wall was found to contain meso-diaminopimelic acid and the whole cell sugars were identified as xylose, glucose, arabinose and galactose. The predominant menaquinones were identified as MK-10(H6) and MK-10(H4). The phospholipid profile was found to consist of diphosphatidylglycerol, phosphatidylethanolamine and phosphatidylinositol. The major fatty acids were identified as C15:0, iso-C16:0, anteiso-C17:0, C17:0 and iso-C15:0. With reference to phenotypic characteristics, phylogenetic data and DNA-DNA hybridization results, strain NEAU-FJL1T can be distinguished from its most closely related strain and classified as a new species, for which the name Plantactinospora solaniradicis sp. nov. is proposed. The type strain is NEAU-FJL1T (= DSM 100596T = CGMCC 4.7284T).

Combining total synthesis and genetic engineering to probe dihydropyran formation in ambruticin biosynthesis.

The ambruticins are a family of potent antifungal polyketide derived natural products isolated from the myxobacterium Sorangium cellulosum. Their unusual structures include a trisubstituted cyclopropyl group and two oxygen heterocycles, a tetrahydropyran (THP) and dihydropyran (DHP). Herein we report a flexible modular approach for the total synthesis of ambruticins which is used to prepare ambruticins F and S as well as in the first total synthesis of 20,21-dihydroambruticin F. The flexible strategy unites 3 fragments via Julia-Kocienski olefinations and provides important standards for investigation of dihydropyran formation in ambruticin biosynthesis. Cultures of wild-type S. cellulosum So ce10 produce mainly ambruticin S and the VS series of metabolites. An efficient electroporation method enabled gene knockout experiments which revealed that the ΔambP-S mutant of S. cellulosum accumulated the bisTHP polyketide 20,21-dihydroambruticin F. In contrast, the ΔambN-S mutant gave ambruticin F with the 20,21-alkene as the major metabolite confirming that AmbP and AmbO (a Rieske enzyme and flavin-dependent monooxygenase respectively) are implicated in 20,21-alkene formation. The results of feeding studies to a Sorangium strain containing only ambP and ambO are in accord with formation of the 20,21-alkene occurring prior to generation of the C3 to C7 dihydroxylated tetrahydropyran in ambruticin biosynthesis.

Liberal surgical laparoscopy reduction for acute intussusception: experience from a tertiary pediatric institute.

The optimal treatment for acute intussusception has not yet been defined. In this study, we explored whether employing a liberal laparoscopic intervention for intussusception could lead to favorable outcomes. We performed a historical control analysis to evaluate the outcomes associated with this liberal surgical management protocol. This liberal surgical management protocol were revised to incorporate a new protocol centered around the laparoscopic approach. In some cases of acute intussusception, liberal laparoscopic exploration and intervention were undertaken without initial hydrostatic or pneumatic reduction. During the study interval, a retrospective review was conducted on a total of 3086 patients. These were categorized into two groups: 1338 cases before May 2019 (pre-protocol group) and 1748 cases after May 2019 (post-protocol group). Surgical intervention rates in the pre-protoco and post-protocol period were 10.2% and 27.4% respectively (odds ratio [OR] = 0.30 [95% CI 0.25-0.37]; p < 0.001). No significant differences were observed in baseline clinical characteristics or demographic features between the two groups. The duration from admission to operation was longer for the pre-protocol group (p = 0.008) than for the post-protocol group. The post-protocol group demonstrated decreases in both intestinal resection (OR = 1.50 [95% CI 0.96-2.35]; p = 0.048) and total recurrent events (OR = 1.27 [95% CI 1.04-1.55]; p = 0.012) compared to the pre-protocol group. Liberal laparoscopic intervention for intussusception may effectively reduce the risk of intestinal resection and total recurrent events, thereby exhibiting promising outcomes for patients with intussusception.

Highly Efficient Production of Menaquinone-7 from Glucose by Metabolically Engineered Escherichia coli.

Menaquinone-7 (MK-7) possesses wide health and medical value, and the market demand for MK-7 has increased. Metabolic engineering for MK-7 production in Escherichia coli still remains challenging due to the characteristics of the competing quinone synthesis, and cells mainly synthesized menaquinones under anaerobic conditions. To increase the production of MK-7 in engineered E. coli strains under aerobic conditions, we divided the whole MK-7 biosynthetic pathway into three modules (MVA pathway, DHNA pathway, and MK-7 pathway) and systematically optimized each of them. First, by screening and enhancing Idi expression, the amounts of MK-7/DMK-7 increased significantly. Then, in the MK-7 pathway, by combinatorial overexpression of endogenous MenA and exogenous UbiE, and fine-tuning the expression of HepPPS, MenA, and UbiE, 70 µM MK-7 was achieved. Third, the DHNA synthetic pathway was enhanced, and 157 µM MK-7 was achieved. By the combinational metabolic engineering strategies and membrane engineering, an efficient metabolic engineered E. coli strain for MK-7 synthesis was developed, and 200 µM (129 mg/L) MK-7 was obtained in shake flask experiment, representing a 306-fold increase compared to the starting strain. In the scale-up fermentation, 2074 µM (1350 mg/L) MK-7 was achieved after 52 h fermentation with a productivity of 26 mg/L/h. This is the highest titer of MK-7 ever reported. This study offers an alternative method for MK-7 production from biorenewable feedstock (glucose) by engineered E. coli. The high titer of our process should make it a promising cost-effective resource for MK-7.