2,476 research outputs found
Poly(3-hydroxybutyrate) production from whey by high density cultivation of recombinant Escherichia coli
No full textRecombinant Escherichia coli strain GCSC 6576, harboring a high-copy-number plasmid containing the Ralstonia eutropha genes for polyhydroxyalkanoate (PHA) synthesis and the E. coli ftsZ gene, was employed to produce poly-(3-hydroxybutyrate) (PHB) from whey, pH-stat fed-batch fermentation, using whey powder as the nutrient feed, produced cellular dry weight and PHB concentrations of 109 g l(-1) and 50 g l(-1) respectively in 47 h. When concentrated whey solution containing 210 g l(-1) lactose was used as the nutrient feed, cellular dry weight and PHB concentrations of 87 g l(-1) and 69 g l(-1) respectively could be obtained in 49 h by pH-stat fed-batch culture. The PHB content was as high as 80% of the cellular dry weight. These results suggest that cost-effective production of PHB is possible by fed-batch culture of recombinant E. coli using concentrated whey solution as a substrate.The PHA biosynthesis genes used in the con-
struction of pSYL107 were kindly provided by A. SteinbuÈ chel. We
thank Mary Berlyn for kindly providing the strain GCSC 6576. We
also thank Anton Middelberg for his valuable suggestions during
his visit to the KAIST. This work was supported by The Korea
Science and Engineering Foundation
Recent advances in polyhydroxyalkanoate production by bacterial fermentation: mini-review
No full textPoly(3-hydroxybutyrate) [P(3HB)] and other polyhydroxyalkanoates (PHAs) have been drawing much attention as biodegradable substitutes for conventional nondegradable plastics. For the economical production of P(3HB), various bacterial strains, either wild-type or recombinant, and new fermentation strategies were developed for the production of P(3HB) with high concentration and productivity. To reduce the cost of carbon substrate, several processes for P(3HB) production from cheap carbon sources were also developed. P(3HB) can now be produced to a content of 80% of cell dry weight with the productivity greater than 4 g/l per h. Fermentation strategy was also developed for the efficient production of medium chain length PHA by high cell density culture. With all these advances, P(3HB) and PHAs can be produced by bacterial fermentation at a cost (ca. $2/kg) similar to that of other biodegradable polymers under development. (C) 1999 Elsevier Science B.V. All rights reserved.This work was supported by the Ministry of Science
and Technology and by LG Chemicals Ltd
Sectoral allocation by gender of Latin American workers over the liberalization period of the 1990s
No full textThe recent restructuring of Latin American economies has renewed interest in the effects of trade liberalization, on labor markets, and on the gender division of labor. The author does not attempt to establish casuality between economic reforms, and the types of jobs that men and women hold. Instead, she provides a detailed description of the trends in male, and female formal, and informal sector participation during the economic reform period in Argentina, Brazil, and Costa Rica. The author first compares the gender composition of the formal, informal wage, and self-employment sectors in a year before reforms (1988 for Argentina, 1989 for Brazil, and Costa Rica), and a year after reforms implementation (1997 for Argentina, 1995 for Brazil and Costa Rica). Although women continued to be more likely than men to work in the informal wage sector, there is no trend of"masculinization"or"feminization"of the informal sector, or any other. Instead, in Argentina men have overtaken women as the most prevalent workers in the informal wage sector, while in Brazil, the opposite has occurred (as men move into self-employment). In Costa Rica there have been no statistical, observable changes. The author then considers the distribution across sectors within each gender group, to identify whether men, and women are more likely to select different sectors in the post-reform period relative to the pre-reform period. Among both men, and women in all three countries (except Brazilian men), workers have become more likely to hold informal wage jobs, and less likely to hold formal sector jobs. Trends in human capital accumulation explain these changes for both men, and women, while changes in gender roles, primarily in homecare and marriage, do not seem to have an effect.Health Monitoring&Evaluation,Labor Policies,Population&Development,Public Health Promotion,Environmental Economics&Policies,Health Monitoring&Evaluation,Environmental Economics&Policies,Population&Development,Banks&Banking Reform,Work&Working Conditions
Effect of post-induction nutrient feeding strategies on the production of bioadhesive protein in Escherichia coli
No full textThe effect of post-induction nutrient feeding strategies on the production of bioadhesive protein using an IPTG inducible expression system in Escherichia coil was investigated. Cells were cultured in an exponential fed-batch mode to the OD600 of ca. 100 (48 gDCW/L) prior to induction. Six different post-induction nutrient feeding strategies (pH-stat, exponential, constant and linear change in feeding rate with three different slopes) were then applied, and bioadhesive protein production was examined. It was found that post-induction cell growth was independent of nutrient feeding rate. However, bioadhesive protein production was significantly affected by post-induction feeding strategies. Linearly changing post-induction feeding rate with a suitable slope allowed production of bioadhesive protein up to 5.3 g/L, which was higher than that obtained by the other post-induction feeding strategies. (C) 1998 John Wiley & Sons, Inc.We thank Dr. Ina Goldberg for providing the E. coli strain
Production of medium-chain-length polyhydroxyalkanoates by high-cell-density cultivation of Pseudomonas putida under phosphorus limitation
No full textHigh-cell-density fed-batch cultures of Pseudomonas putida were carried out for the production of medium-chain-length polyhydroxyalkanoates (PHAs) using oleic acid as a carbon source. By employing an optimal feeding strategy without the limitation of any nutrient, a high cell concentration of 173 g/L was achieved, but the PHA concentration and PHA content were only 32.3 g/L and 18.7 wt%, respectively. To increase the PHA concentration and content, phosphorus limitation was applied during fed-bath culture by reducing the initial KH,PO, concentration. When the initial KH,PO, concentration was reduced to 4 g/L, cell concentration, PHA concentration, and PHA content obtained in 38 h were 141 g/L, 72.6 g/L, and 51.4 wt%, respectively, resulting in a high productivity of 1.91 g PHA/L per hour. (C) 2000 John Wiley & Sons, Inc. Biotechnol Bioeng 68: 466-470, 2000.The authors thank Dr. Frank Bartels for providing us with the P.
putida strain
The interactional patterns of hearing, deaf/hard of hearing (D/HH) students participating in Hong Kong sign bilingual and co-enrollment classroom
No full textCo-enrollment offers D/HH student social integration opportunities with hearing peers. When co-enrollment partners with sign bilingualism, all students, deaf and hearing, are immersed in a classroom environment where they can interact and learn from other's language and culture. The aims of this study were to investigate the frequency and pattern of classroom interaction in terms of language use and Initiation-Response-Follow-up (IRF) patterns among the students with different hearing status in the Hong Kong sign bilingual and co-enrollment (SLCO) classroom over a period of six years.
The interaction patterns and language use of 6 D/HH students and their 25 hearing peers were followed for 6 years from Primary One to Six in a SLCO classroom. A mixed-method approach was adopted using qualitative (naturalistic observation and semi-structured interviews) and quantitative (systematic observations based on video data) research methods.
Results showed that students' classroom participation and frequency of interactions increased significantly over time. Hearing status affects neither the quantity of classroom participation nor their interlocutors in classroom interaction. Student-student and teacher-student interaction increased significantly after the initial observation period. D/HH-D/HH, hearing-hearing and D/HH-hearing interactions all increased in quantity over time. There was an increase in the use of Hong Kong Sign Language (HKSL) with students of different hearing status over time. The number of D/HH students' initiation moves out-numbered their hearing peers during the initial observation period. In the later observation periods, both D/HH and hearing students' initiation, response and follow-up moves increased over time.
Findings of this study filled the gap of the previous literatures by exploring the language use of D/HH students and their hearing peers in the natural SLCO classroom. Favorable classroom ecologies which could facilitate D/HH and hearing peer or teacher interactions were identified. This longitudinal study is the first in the field which used systematic observation to explore D/HH and hearing students' IRF patterns at different stages of their school life.
This study indicates that D/HH and hearing students in a SLCO setting can develop skills for interacting with each other. Moreover, the classroom shifted from teacher-centered to a more student-centered one. Co-enrollment seemed to facilitate D/HH-hearing and D/HH-D/HH interactions, in other words, benefiting both D/HH and hearing students.published_or_final_versionEducationDoctoralDoctor of Philosoph
Metabolic analysis of poly(3-hydroxybutyrate) production by recombinant Escherichia coli
No full textPoly(3-hydroxybutyrate) (PHB) production by fermentation was examined under both restricted- and ample-oxygen supply conditions in a single fed-batch fermentation. Recombinant Escherichia coli transformed with the PHB production plasmid pSYL107 was grown to reach high cell density (227 g/l dry cell weight) with a high PHB content (78% of dry cell weight), using a glucose-based minimal medium. A simple flux model containing 12 fluxes was developed and applied to the fermentation data. A superior closure (95%) of the carbon mass balance was achieved. When the data were put into use, the results demonstrated a surprisingly large excretion of formate and lactate. Even though periods of severe oxygen limitation coincided with rapid acetate and lactate excretion, PHB productivity and carbon utilization efficiency were not significantly impaired. These results are very positive in reducing oxygen demand in an industrial PHA fermentation without sacrificing its PHA productivity, thereby reducing overall production costs
Prevalence of GERD in Southeast Asian countries
No full textThe reported population prevalence of GERD in eastern Asia ranged from 2.5% to 6.7% for at least weekly symptoms of heartburn and/or acid regurgitation. Typical GERD symptoms are consistently less common among the general populations of Asia than those in the West which have a prevalence of around 20% for weekly refl ux symptoms. No reliable data are available on the prevalence of esophagitis in the general population. In case studies the prevalence of refl ux esophagitis ranged from 3.4% to 16.3%. A large study in Hong Kong in patients undergoing routine or emergency upper endoscopy (n=16,606) showed that 3.8% of the patients had esophagitis demonstrated by endosocpy and the majority (94%) had Los Angeles Classifi cation Grade A or B esophagitis and only 14 patients (0.08%) had esophageal stricture. Rosaida et al. have shown that in a prospective study, 65.5% of their patients had NERD. In another study from Hong Kong, it was found that 46.7% (215 of 460 subjects) of patients with typical refl ux symptoms had no endoscopic evidence of esophagitis. In a study from Singapore, patients with NERD were signifi cantly younger, more likely to have minor psychiatric morbidity and were less likely to respond to proton pump inhibitors (PPI) when compared with patients with erosive esophagitis. In summary, the prevalence of refl ux esophagitis appears to be lower in Asian population and the disease spectrum is milder in Asians. Prevalence of Barrett's varies between different countries. In a study of multi-ethnic Malaysian population, Barrett's esophagus was reported in 1.6% of those undergoing elective endoscopy for upper abdominal or refl ux complaints. A much lower prevalence was found in southern Chinese patients undergoing upper endoscopy, of whom only 0.06% were found (n=22,628). More data are required to determine the true prevalence of Barrett's esophagus in Asians. The prevalence of GERD in Asia may be increasing. In a 1999 re-survey of a cohort of community residents in Singapore who were interviewed in an earlier study in 1994, Lim et al. reported a more than 6 fold increase in the reporting of refl ux symptoms, from a prevalence of 1.6% to a prevalence of 9.9%. In a 1-year follow up study in Hong Kong, Wong et al. reported an increase in the annual, monthly and weekly prevalence of GERD from 29.8%, 8.9% and 2.5% to 34.1%, 10.1% and 2.7%, respectively. REFERENCES: 1. Wong WM, Lai KC, Lam KF, Hui WM, Hu WH, Lam CL, Xia HH, Huang JQ, Chan CK, Lam SK, Wong BC. Prevalence, clinical spectrum and health care utilization of gastro-oesophageal refl ux disease in a Chinese population: a population-based study. Aliment Pharmacol Ther 2003;18:595-604. 2. Wong WM, Lai KC, Lam KF, Hui WM, Huang JQ, Xia HH, Hu WH, Lam CL, Chan CK, Lam SK, Wong BC. Onset and disappearance of refl ux symptoms in a Chinese population: a 1-year follow-up study. Aliment Pharmacol Ther 2004;20:803-12. 3. Wong BC, Kinoshita Y. Systematic review on epidemiology of gastroesophageal refl ux disease in Asia. Clin Gastroenterol Hepatol 2006;4:398-407. 4. Wong WM, Lam SK, Hui WM, Lai KC, Chan CK, Hu WH, Xia HH, Hui CK, Yuen MF, Chan AO, Wong BC. Long-term prospective follow-up of endoscopic oesophagitis in southern Chinese--prevalence and spectrum of the disease. Aliment Pharmacol Ther 2002;16:2037-42.link_to_subscribed_fulltex
MOESM1 of Hand hygiene – social network analysis of peer-identified and management-selected change agents
No full textAdditional file 1. Lee YF, McLaws ML, Ong LM, Husin SA, Chua HH, Wong SY, Pittet D, Zingg W. Hand Hygiene promotion delivered by change agents – two attitudes, similar outcome. InfectionControl & Hospital Epidemiology. 2019 (in press)
Why liberalization alone has not improved agricultural productivity in Zambia : the role of asset ownership and working capital constraints
No full textThe authors use a large panel data set from Zambia to examine factors that could explain the relatively lackluster performance of the country's agricultural sector after liberalization. Zambia's liberalization significantly opened the economy but failed to alter the structure of productionor help realize efficiency gains. They reach two main conclusions. First, not owning productive assets (in Zambia, draft animals and implements) limits improvements in agricultural productivity and household welfare. Owning oxen increases income directly, allows farmers to till their fields efficiently when rain is delayed, increases the area cultivated, and improves access to credit and fertilizer markets. Second, the authors reject the hypothesis that the application of fertilizer is unprofitable because of high input prices. Rather, fertilizer use appears to have declined because of constraints on supplies, which government intervention exacerbated instead of alleviating. (Extending the use of fertilizer to the many producers not currently using it would be profitable, but increasing the amount applied by the few producers who now have access to it would not be.) Policies to foster accumulation of the assets needed for agricultural production (including draft animals and implements) and to provide complementary public goods (education, credit, and good agricultural extension services) could greatly help reduce poverty and improve productivity.Economic Theory&Research,Environmental Economics&Policies,Labor Policies,Banks&Banking Reform,Agricultural Knowledge&Information Systems,Environmental Economics&Policies,Economic Theory&Research,Banks&Banking Reform,Agricultural Knowledge&Information Systems,Agricultural Research
- …
