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丙酮丁醇梭菌半胱氨酸合成途径中铁氧还蛋白和胱硫醚-γ-裂解酶基因功能 被引量:1
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作者 徐荆 刘自勇 +3 位作者 朱海峰 高亮亮 张培玉 李福利 《微生物学报》 CAS CSCD 北大核心 2020年第3期570-581,共12页
【目的】探究丙酮丁醇梭菌半胱氨酸合成代谢途径上铁氧还蛋白和胱硫醚-γ-裂解酶基因的功能。【方法】使用ClosTron系统对半胱氨酸合成途径上的铁氧还蛋白基因(fer)和胱硫醚-γ-裂解酶基因(mccB)进行失活,得到突变株;在不同硫源的培养... 【目的】探究丙酮丁醇梭菌半胱氨酸合成代谢途径上铁氧还蛋白和胱硫醚-γ-裂解酶基因的功能。【方法】使用ClosTron系统对半胱氨酸合成途径上的铁氧还蛋白基因(fer)和胱硫醚-γ-裂解酶基因(mccB)进行失活,得到突变株;在不同硫源的培养基中进行分批发酵,分析突变株的生长特点;通过pH控制,使用限磷的连续发酵方法将丙酮丁醇梭菌维持在产酸期和产溶剂期,分析野生型菌株和突变株在连续发酵中的生长情况。【结果】成功构建Δfer和ΔmccB突变株。在分批发酵中,敲除fer基因的突变株无法利用硫酸盐作为硫源,但添加亚硫酸盐或半胱氨酸可以使其恢复生长;在以半胱氨酸为唯一硫源进行分批发酵时,其终浓度1 mmol/L时不会影响野生型与Δfer突变株的生长,但高于1 mmol/L时生长均会受到抑制。在连续发酵中,Δfer突变株不能在产溶剂阶段生长,添加过量的半胱氨酸也不能恢复生长;敲除mccB基因的突变株仍能在添加甲硫氨酸的培养基中生长,但最大OD仅为野生型的57%;相较于野生型,ΔmccB突变株在产酸期和产溶剂期的生长均受到抑制。【结论】fer基因为半胱氨酸合成途径中硫酸盐还原为亚硫酸盐的关键基因,其控制合成的半胱氨酸不能完全由外源的半胱氨酸替代,敲除后对生长的抑制主要表现在连续发酵中的产溶剂阶段。mccB基因参与调控甲硫氨酸转化为半胱氨酸的过程,其敲除会影响甲硫氨酸到半胱氨酸的转化,但不会阻断该生物反应过程。 展开更多
关键词 硫元素代谢 丙酮丁醇梭菌 磷酸限制连续发酵 ClosTron 系统
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The Impact of Farmland Transfers on Agricultural Investment in China:A Perspective of Transaction Cost Economics 被引量:6
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作者 liangliang gao Dingqiang Sun Cuiping Ma 《China & World Economy》 SCIE 2019年第1期93-109,共17页
There is growing concern that farmland transfers lead to less agricultural investment, which may adversely affect agricultural productivity growth in China.Prior research has primarily focused on the differences betwe... There is growing concern that farmland transfers lead to less agricultural investment, which may adversely affect agricultural productivity growth in China.Prior research has primarily focused on the differences between owned cultivated land and rented plots,but little is known about how farmland transfers between relatives,which are popular in rural China,specifically affect agricultural investment.In this paper,we present a conceptual framework of transaction cost economics to compare different contracting strategies in China's farmland rental markets.As farmland rental markets in China are immature,land transfer between relatives establishes bilateral governance,which has the advantage of addressing the opportunistic activities of both parties and can ultimately increase investment by tenants.Based on data from two waves of household surveys,we empirically examine the impact of bilateral governance on the application of organic fertilizer,an indicator for agricultural investment.Our findings show that apart from economic factors, kinship is important to the functioning of farmland rental markets in rural areas. 展开更多
关键词 AGRICULTURAL INVESTMENT FARMLAND rental market GOVERNANCE structure TRANSACTION cost ECONOMICS
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Identifying the Turning Point of the Urban-Rural Relationship: Evidence from Macro Data 被引量:7
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作者 liangliang gao Jiao Yan Yue Du 《China & World Economy》 SCIE 2018年第1期106-126,共21页
The urban and rural dual structure is a defining characteristic of the social and economic development process in China. With rapid urbanization, remarkable development of agriculture and rural modernization, the rela... The urban and rural dual structure is a defining characteristic of the social and economic development process in China. With rapid urbanization, remarkable development of agriculture and rural modernization, the relationship between urban and rural areas is undergoing significant changes in China. Using macro data, we find that the relationship between urban and rural areas started to change in 2010. The transition has mainly been reflected in three dimensions: agriculture, rural areas and farmers. First, agricultural versatility has gradually increased, and the number of participants in leisure agriculture and rural tourism has grown rapidly since 2010. Second, the rural employment rate has risen gradually, and the share of rural employees in the tertiary sector has grown markedly. Third, the urban-rural income ratio and consumption ratio have begun to decrease, and the levels of consumption of domestic tourism by urban and rural residents are becoming small. 展开更多
关键词 agricultural diversification urban-rural consumption ratio urban-rural income ratio urban-rural relationship
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A review of hydrological/water-quality models 被引量:3
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作者 liangliang gao Daoliang LI 《Frontiers of Agricultural Science and Engineering》 2014年第4期267-276,共10页
Water quality models are important in predicting the changes in surface water quality for environmental management.A range of water quality models are wildly used,but every model has its advantages and limitations for... Water quality models are important in predicting the changes in surface water quality for environmental management.A range of water quality models are wildly used,but every model has its advantages and limitations for specific situations.The aim of this review is to provide a guide to researcher for selecting a suitable water quality model.Eight well known water quality models were selected for this review:SWAT,WASP,QUALs,MIKE 11,HSPF,CE-QUAL-W2,ELCOM-CAEDYM and EFDC.Each model is described according to its intended use,development,simulation elements,basic principles and applicability(e.g.,for rivers,lakes,and reservoirs and estuaries).Currently,the most important trends for future model development are:(1)combination models—individual models cannot completely solve the complex situations so combined models are needed to obtain the most appropriate results,(2)application of artificial intelligence and mechanistic models combined with nonmechanistic models will provide more accurate results because of the realistic parameters derived from nonmechanistic models,and(3)integration with remote sensing,geographical information and global position systems(3S)-3S can solve problems requiring large amounts of data. 展开更多
关键词 water quality models APPLICATIONS future trends
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