Advances in the production of chemicals by organelle compartmentalization in Saccharomyces cerevisiae / 生物工程学报

As a generally-recognized-as-safe microorganism, Saccharomyces cerevisiae is a widely studied chassis cell for the production of high-value or bulk chemicals in the field of synthetic biology. In recent years, a large number of synthesis pathways of chemicals have been established and optimized in S. cerevisiae by various metabolic engineering strategies, and the production of some chemicals have shown the potential of commercialization. As a eukaryote, S. cerevisiae has a complete inner membrane system and complex organelle compartments, and these compartments generally have higher concentrations of the precursor substrates (such as acetyl-CoA in mitochondria), or have sufficient enzymes, cofactors and energy which are required for the synthesis of some chemicals. These features may provide a more suitable physical and chemical environment for the biosynthesis of the targeted chemicals. However, the structural features of different organelles hinder the synthesis of specific chemicals. In order to ameliorate the efficiency of product biosynthesis, researchers have carried out a number of targeted modifications to the organelles grounded on an in-depth analysis of the characteristics of different organelles and the suitability of the production of target chemicals biosynthesis pathway to the organelles. In this review, the reconstruction and optimization of the biosynthesis pathways for production of chemicals by organelle mitochondria, peroxisome, golgi apparatus, endoplasmic reticulum, lipid droplets and vacuole compartmentalization in S. cerevisiae are reviewed in-depth. Current difficulties, challenges and future perspectives are highlighted.

Intrinsically disordered proteins (IDPs) and the impact on cell stress resistance / 生物工程学报

Intrinsically disordered proteins (IDPs) are proteins or protein regions that fail to get folded into definite three-dimensional structures but participate in various biological processes and perform specific functions. Defying the traditional protein "sequence-structure-function" paradigm, they enrich the protein "structure-function" diversity. Ubiquitous in organisms, they show extreme hydrophilicity, charged amino acids, and highly repetitive amino acid sequences, with simple arrangement. As a result, they feature highly variable binding affinities and high coordination, which facilitate their functions. IDPs play an important role in cell stress response, which can improve the tolerance to a variety of stresses, such as freezing, high salt, heat shock, and desiccation. In this study, we briefed the characteristics, classifications, and identification of IDPs, summarized the molecular mechanism in improving cell stress resistance, and described the potential applications.

Progress in studies on production of chemicals from xylose by Saccharomyces cerevisiae / 生物工程学报

Effective utilization of xylose is a basis for economic production of biofuels or chemicals from lignocellulose biomass. Over the past 30 years, through metabolic engineering, evolutionary engineering and other strategies, the metabolic capacity of xylose of the traditional ethanol-producing microorganism Saccharomyces cerevisiae has been significantly improved. In recent years, the reported results showed that the transcriptome and metabolome profiles between xylose and glucose metabolism existed significant difference in recombinant yeast strains. Compared with glucose, the overall process of xylose metabolism exhibits Crabtree-negative characteristics, including the limited glycolytic pathway activity, which reduces the metabolic flux of pyruvate to ethanol, and the enhanced cytosolic acetyl-CoA synthesis and respiratory energy metabolism. These traits are helpful to achieve efficient synthesis of downstream products using pyruvate or acetyl-CoA as precursors. This review provides a detailed overview on the modification and optimization of xylose metabolic pathways in S. cerevisiae, the characteristics of xylose metabolism, and the construction of cell factories for production of chemicals using xylose as a carbon source. Meanwhile, the existed difficulties and challenges, and future studies on biosynthesis of bulk chemicals using xylose as an important carbon source are proposed.

Progress in research of pentose transporters and C6/C5 co-metabolic strains in Saccharomyces cerevisiae / 生物工程学报

One of the requirements for increasing the economic profitability on the large-scale production of second-generation ethanol and other bio-chemicals using lignocellulose biomass as raw materials is efficient hexose and pentose utilization. Saccharomyces cerevisiae, the traditional ethanol producer, is an attractive chassis cell due to its robustness towards harsh environmental conditions and inherent advantages. But S. cerevisiae cannot utilize pentose. The precision construction of suitable strains for second-generation bio-ethanol production has been taken for more than three decades based on the principle of metabolic engineering and synthetic biology. The resulting strains have improved significantly co-fermentation of glucose and xylose. Recently, much attentions have been focused on sugar transport, which is one of the limiting but formerly ignored step for ethanol production from both glucose and xylose, to get the desired state that different sugars could efficiently delivered by their individual specific transporters. In this paper, the progress on sugar transporters of S. cerevisiae was reviewed, and the research status of xylose and/or L-arabinose metabolic engineering in S. cerevisiae were also presented.

In vitro osteogenic differentiation of bone marrow mesenchymal stem cells from ovariectomied osteoporotic rats / 中国组织工程研究

BACKGROUND:Cytological studies show that bone marrow mesenchymal stem cel s play an important role in postmenopausal osteoporosis mechanism. OBJECTIVE:To study the osteogenic differentiation in vitro of bone marrow mesenchymal stem cel s from ovariectomied osteoporotic rats. METHODS:The osteoporotic animal model was established by performing ovariectomy in the 6-month-old female Sprague-Dawley rats. There were four groups:bone marrow mesenchymal stem cel s control group, bone marrow mesenchymal stem cel s osteoporosis group, bone marrow mesenchymal stem cel s osteogenic induction group and oseogenesis induction group. Bone marrow mesenchymal stem cel s were isolated from the rats of control group and oseogenesis induction group by means of the whole bone marrow adherence method and cultured to the 3rd generation. Then the bone marrow mesenchymal stem cel s were used in al the experiments. Cel morphology was observed under the inverted phase contrast microscope, cel cycle and proliferation index of bone marrow mesenchymal stem cel s were detected by flow cytometry. After osteogenic induction, the expression level of alkaline phosphatase was detected, and the fornation of calcium nodes of bone marrow mesenchymal stem cel s were marked by alizarin red staining. RESULTS AND CONCLUSION:The cel s in the osteogenic induction group and oseogenesis induction group had the morphology of osteobalsts, and the change of morphology of the cel s in the oseogenesis induction group was relatively tardiness. The proliferation index in the control group was higher than that in the osteoporosis group (P<0.05);expression level of alkaline phosphatase in the osteogenic induction group was significantly higher than that in the oseogenesis induction group (P<0. 05), and the control group was significantly higher than the oseogenesis group (P<0.05). The alizarin red staining of the cel s in the osteogenic induction group was positive, while negative in the control group and the oseogenesis group;the staining in the osteogenic induction group was stronger than that in the oseogenesis induction group. These findings indicate that both the proliferative potential and the osteogenic potential of bone marrow mesenchymal stem cel s from the ovariectomized osteoporotic rats are decreased, which may be related with the ostoeporosis pathogensis of ovariectomied rats.

Correlation between bone mineral density and serum vascular endothelial growth factor levels in ovariectomized rats / 中国组织工程研究

BACKGROUND: Vascular endothelial growth factor play an important role in promoting healing of osteoporotic fractures, but whether it can affect the bone mineral density is not clear. OBJECTIVE: To observe the correlation between serum vascular endothelial growth factor, bone mineral density and the number of osteoblasts in the ovariectomized rats. METHODS: Forty female Sprague-Dawley rats were randomly divided into ovariectomized group and control group. After 3 months, the bone mineral density of the whole body, femur and lumbar spine was measured. Rat enzyme-linked immunosorbent assay kit was used to measure the level of serum vascular endothelial growth factor. Then, the rats in two groups received femoral metaphyseal fixation, decalcified, dehydrated, embeding in paraffin, slicing and hematoxylin-eosin staining. Each slice was free to take five fields of view (10×40) in order to count the osteoblasts of femur distal metaphysis under optical microscope. RESULTS AND CONCLUSION: After ovariectomized for 3 months, the rats body mass was increased significantly (P 0.05), and the difference of the osteoblast number between ovariectomized group and control group was not significant (P > 0.05). This indicated that there was no correlation between bone mineral density and the number of osteoblasts and vascular endothelial growth factor level in the ovariectomized group and the control group. These findings suggest that the bone mineral density is reduced and the body mass is increased in the ovariectomized rats, and the reduced bone mineral density of ovariectomized rats may be irrelevant with the change of serum vascular endothelial growth factor.

Screening of high lipid production Trichosporon fermentans mutants by transposon tagging mTn-lacZ/leu2 insertion / 生物工程学报

To improve microbial lipid production, we inserted mTn-lacZ/leu2 into Trichosporon fermentans 2.1368-Leu(-) to obtain high lipid production mutants. By observing the LacZ chromogenic change, the positive reaction between Cerulenin (inhibitor of fatty acid synthase) and phosphate vanillin, a higher lipid-producing mutant 2.1368-Leu(-)-7 grown on corn-stalk hydrolysate was obtained. The lipid content of this mutant reached 38.30% (8.97% higher than that of the control) and the lipid production rate was 8.35% (20.63% higher than that of the control). The rate of sugar utilization was 77%, meaning that 100 g corn-stalk could be converted to 8.32 g lipid. The study provided an effective method for microbial lipid production by using cheap raw materials for biodiesel.

Progress and strategies on bioethanol production from lignocellulose by consolidated bioprocessing (CBP) using Saccharomyces cerevisiae / 生物工程学报

Ethanol production from lignocelluloses of consolidated bioprocessing (CBP) is a system in which cellulase and hemicellulase production, substrate hydrolysis, and fermentation are combined or partially combined by ethanologen microorganisms that express cellulolytic or hemicellulolytic enzymes or engineering cellulolytic microorganisms with ethanol production properties. Due to its potential for significant cost reduction, CBP is receiving more and more attention. In this review article, we discuss the factors that influence the expression level of cellulases in Saccharomyces cerevisiae and updated progress in bioethanol production from lignocellulose by the CBP strategy using the yeast species.

Inhibitors and their effects on Saccharomyces cerevisiae and relevant countermeasures in bioprocess of ethanol production from lignocellulose--a review / 生物工程学报

The pretreatment of raw materials is necessary for ethanol production from lignocellulose, however, a variety of compounds which inhibit the fermenting microorganism such as Saccharomyces cerevisiae are inevitably formed in this bioprocess. Based on their chemical properties, the inhibitors are usually divided into three major groups: weak acids, furaldehydes and phenolic compounds. These compounds negatively affect the growth of S. cerevisiae, ethanol yield and productivity, which is one of the significant hurdles for the development of large-scale ethanol production from lignocellulose. We address here the origins of the three kinds of inhibitors and their mechanisms to S. cerevisiae. We also discuss the strategies of improving the fermentation performance of yeast, including detoxification of the pretreated substrates, enhancement of yeast tolerance and also fermentation control to reduce the effects of the inhibitors. The methods used in enhancing the yeast tolerance are traditional mutagenic breeding integrated with strains evolution under the suitable selective pressure, and metabolic engineering by introducing and/or overexpressing genes encoding enzymes such as furfural reductase, laccase and phenylacrylic acid decarboxylase, that confer the S. cerevisiae strains resistance towards specific inhibitors.

Acinic Cell Carcinoma of salivary Glands -A Clinicopathological Analysis of 5Q cases / 第三军医大学学报

Fifty cases of acinic cell carcinoma(ACC) of salivary glands were observed in a period of 22 years(l960-1982) in this hospital. 25 tumors out of the 50 occurred in the parotid gland, 7 in the submaxillary gland, and 18 in other minor salivary glands. Conventional microscopy revealed that ACC of salivary glands are composed of granulated acinic cells, clear cells, vacuolated cells, and intercalated duct cells. According to the different histological features, the authors suggest that ACC are to be classified into 6 types: cystic papillary, solid ethmoid, tra-beculopapillary, acinic adenoid, acinic nestlike and diffuse types. This classification facilitates the clinicians and pathologists to grasp the pathological cha- racteristies and diagnostic criteria and assessable prognosis and to accumulate the clinical material for research purposes.Thirty-seven patients out of the 50 have been followed up for years, the longest up to 19 years. 14 patients(37.8%)developed local recurrences. The five and ten year survival rates are 62.2% and 37.8% respectively.The differential diagnosis, histochemistry, histogenesis, and prognosis of ACC were discussed with a brief review of the literature concerned. Our data supports the assumption that ACC originates from the intercalated duct cells rather than from fully differentiated serous cells.