Engineered Streptomyces lividans Strains for Optimal Identification and Expression of Cryptic Biosynthetic Gene Clusters

Streptomyces lividans is a suitable host for the heterologous expression of biosynthetic gene clusters (BGCs) from actinomycetes to discover “cryptic” secondary metabolites. To improve the heterologous expression of BGCs, herein we optimized S. lividans strain SBT5 via the stepwise integration of three global regulatory genes and two codon-optimized multi-drug efflux pump genes and deletion of a negative regulatory gene, yielding four engineered strains. All optimization steps were observed to promote the heterologous production of polyketides, non-ribosomal peptides, and hybrid antibiotics. The production increments of these optimization steps were additional, so that the antibiotic yields were several times or even dozens of times higher than the parent strain SBT5 when the final optimized strain, S. lividans LJ1018, was used as the heterologous expression host. The heterologous production of these antibiotics in S. lividans LJ1018 and GX28 was also much higher than in the strains from which the BGCs were isolated. S. lividans LJ1018 and GX28 markedly promoted the heterologous production of secondary metabolites, without requiring manipulation of gene expression components such as promoters on individual gene clusters. Therefore, these strains are well-suited as heterologous expression hosts for secondary metabolic BGCs. In addition, we successfully conducted high-throughput library expression and functional screening (LEXAS) of one bacterial artificial chromosome library and two cosmid libraries of three Streptomyces genomes using S. lividans GX28 as the library-expression host. The LEXAS experiments identified clones carrying intact BGCs sufficient for the heterologous production of piericidin A1, murayaquinone, actinomycin D, and dehydrorabelomycin. Notably, due to lower antibiotic production, the piericidin A1 BGC had been overlooked in a previous LEXAS screening using S. lividans SBT5 as the expression host. These results demonstrate the feasibility and superiority of S. lividans GX28 as a host for high-throughput screening of genomic libraries to mine cryptic BGCs and bioactive compounds

Preparation and Properties of Viscose Rayon/O-carboxymethyl Chitosan Antibacterial Fibers

ABSTRACT Antimicrobial viscose rayon/O-carboxymethyl chitosan fibers (VCMFs) were manufactured by spinning the mixture of O-carboxymethyl chitosan (O-CMCS) xanthate and cellulose xanthate via the viscose process. The structure, morphology and mechanical properties were investigated by infrared, scanning electron microscopy, transmission electron microscope and tensile test. The results show that the blend fibers of cellulose and O-CMCS were satisfactorily prepared and the two polymers were mixed homogeneously. VCMFs display striation along the fiber similar to those of viscose rayon fibers, and their mechanical properties are close to that of viscose rayon. With O-CMCS blended, VCMFs showed good moisture absorption and antibacterial activity against E.coli

Simultaneous improvement of strength and ductility in ZK60 magnesium alloy by constructing the bimodal grain structure

In this study, the microstructure and mechanical properties of the commercial magnesium (Mg) ZK60 alloy were conducted to promote the application of Mg alloys. Scanning electron microscopy, tensile and compression tests, electron back scattering diffraction, transmission electron microscope and visco-plasticity self-consistent methods were employed to analyze the microstructure evolution and the strengthening and toughening mechanisms. By direct extrusion in the as-cast state, a bimodal microstructure was obtained, and the mechanical properties were enhanced. The ZK60 alloy, with a bimodal grain structure, exhibited a good combination of strength and ductility. The tensile yield strength (TYS), ultimate tensile strength (UTS), compressive yield strength (CYS) and fracture elongation (FE) reached 272 MPa, 347 MPa, 289 MPa, and 36.2%, respectively. Compared with the traditional extrusion ZK60 alloy, the increment in TYS, UTS, CYS, and FE was 15 MPa, 31 MPa, 25 MPa and 8.6%, respectively. The formation of the bimodal structure in the ZK60-CE sample is attributed to the combination of the PSN and Zener pinning effects. The improvement in strength is mainly attributed to the residual dislocations in the un-DRXed grains and the good ductility is ascribed to the activation of the non-basal slip. This study provides a low-cost and efficient strategy for the preparation of the bimodal structure by regulating the pre-extrusion microstructure to improve mechanical properties

Ultrafine-grained Mg alloy: Preparation, properties, design strategy

As the lightest metal structural materials, Mg alloys have great application potential in transportation, aerospace, and biomedicine. However, the further application is hindered by their low strength, plasticity, and poor corrosion resistance. The preparation of Mg alloys with ultra-fine grain (UFG) structure is regarded as a good solution to improve their performance, and has been reported by a large number of literatures. The purpose of this paper is to summarize the development of fabrication processes of UFG Mg alloys and the effects of UFG structure on the mechanical properties and corrosion resistance. In essence, this review aims to elucidate the evolution and current state of UFG structure in Mg alloys. Additionally, it seeks to expound upon the strategies for designing and preparing these structures and shed light on the future development trends. The ultimate goal is to advance the utilization of UFG Mg alloys in both structural and functional materials

Insulin secretory capacity and sensitivity of women in the GDM and control cohorts at fasting and a 1-h OGTT.

<p>Data are means ± SD.</p><p>GDM, gestational diabetes mellitus; OGTT, oral glucose tolerance test; HOMA-IR, HOMA insulin resistance index; HOMA-B, HOMA pancreatic β-cell function; HOMA-ISI, HOMA insulin sensitivity index; CIR, corrected insulin response</p><p>Insulin secretory capacity and sensitivity of women in the GDM and control cohorts at fasting and a 1-h OGTT.</p

Multivariable conditional logistic regression analysis of explanatory variables at fasting and a 1-h OGTT against outcome of GDM.

<p>GDM, gestational diabetes mellitus; OGTT, oral glucose tolerance test; hs-CRP, high-sensitivity C reactive protein; HFR, high fluorescence reticulocytes; MCV, mean cell volume; MONO, monocyte; NEUT, neutrophil; RBC, red blood cell; RET, reticulocyte</p><p>Multivariable conditional logistic regression analysis of explanatory variables at fasting and a 1-h OGTT against outcome of GDM.</p

Sociodemographic characteristics of women in the GDM and control cohorts.

<p>* Maternal age, gravidity, parity, BMI and gestational weeks were determined at the time of recruitment. Control subjects were matched against subjects with GDM.</p><p>GDM, gestational diabetes mellitus; BMI, body mass index</p><p>Sociodemographic characteristics of women in the GDM and control cohorts.</p