抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

世界経済・社会統計 = World development indicators

Increasing population and consumption are placing unprecedented demands on agriculture and natural resources. Today, approximately a billion people are chronically malnourished while our agricultural systems are concurrently degrading land, water, biodiversity and climate on a global scale. To meet the world's future food security and sustainability needs, food production must grow substantially while, at the same time, agriculture's environmental footprint must shrink dramatically. Here we analyse solutions to this dilemma, showing that tremendous progress could be made by halting agricultural expansion, closing 'yield gaps' on underperforming lands, increasing cropping efficiency, shifting diets and reducing waste. Together, these strategies could double food production while greatly reducing the environmental impacts of agriculture.

https://escholarship.org/content/qt6xw5g085/qt6xw5g085.pdf?t=ovfwpc

Solutions for a cultivated planet

Most prior studies have found that substituting biofuels for gasoline will reduce greenhouse gases because biofuels sequester carbon through the growth of the feedstock. These analyses have failed to count the carbon emissions that occur as farmers worldwide respond to higher prices and convert forest and grassland to new cropland to replace the grain (or cropland) diverted to biofuels. By using a worldwide agricultural model to estimate emissions from land-use change, we found that corn-based ethanol, instead of producing a 20% savings, nearly doubles greenhouse emissions over 30 years and increases greenhouse gases for 167 years. Biofuels from switchgrass, if grown on U.S. corn lands, increase emissions by 50%. This result raises concerns about large biofuel mandates and highlights the value of using waste products.

/pdf/use-of-u-s-croplands-for-biofuels-increases-greenhouse-gases-48xnl16nx3.pdf

Use of U.S. Croplands for Biofuels Increases Greenhouse Gases Through Emissions from Land-Use Change

Sustainability is a key principle in natural resource management, and it involves operational efficiency, minimisation of environmental impact and socio-economic considerations; all of which are interdependent. It has become increasingly obvious that continued reliance on fossil fuel energy resources is unsustainable, owing to both depleting world reserves and the green house gas emissions associated with their use. Therefore, there are vigorous research initiatives aimed at developing alternative renewable and potentially carbon neutral solid, liquid and gaseous biofuels as alternative energy resources. However, alternate energy resources akin to first generation biofuels derived from terrestrial crops such as sugarcane, sugar beet, maize and rapeseed place an enormous strain on world food markets, contribute to water shortages and precipitate the destruction of the world's forests. Second generation biofuels derived from lignocellulosic agriculture and forest residues and from non-food crop feedstocks address some of the above problems; however there is concern over competing land use or required land use changes. Therefore, based on current knowledge and technology projections, third generation biofuels specifically derived from microalgae are considered to be a technically viable alternative energy resource that is devoid of the major drawbacks associated with first and second generation biofuels. Microalgae are photosynthetic microorganisms with simple growing requirements (light, sugars, CO 2 , N, P, and K) that can produce lipids, proteins and carbohydrates in large amounts over short periods of time. These products can be processed into both biofuels and valuable co-products. This study reviewed the technologies underpinning microalgae-to-biofuels systems, focusing on the biomass production, harvesting, conversion technologies, and the extraction of useful co-products. It also reviewed the synergistic coupling of microalgae propagation with carbon sequestration and wastewater treatment potential for mitigation of environmental impacts associated with energy conversion and utilisation. It was found that, whereas there are outstanding issues related to photosynthetic efficiencies and biomass output, microalgae-derived biofuels could progressively substitute a significant proportion of the fossil fuels required to meet the growing energy demand.

/pdf/biofuels-from-microalgae-a-review-of-technologies-for-1t1wwr5e69.pdf

Biofuels from microalgae—A review of technologies for production, processing, and extractions of biofuels and co-products

Food security, farming, and climate change to 2050: challenges to 2050 and beyond

As the global population grows and incomes in poor countries rise, so too, will the demand for food, placing additional pressure on sustainable food production. Climate change adds a further challenge, as changes in temperature and precipitation threaten agricultural productivity and the capacity to feed the world's population. This study assesses how serious the danger to food security might be and suggests some steps policymakers can take to remedy the situation.

Food security, farming, and climate change to 2050: Scenarios, results, policy options

Most prior studies have found that substituting biofuels for gasoline will reduce greenhouse gases because biofuels sequester carbon through the growth of the feedstock These analyses have failed to count the carbon emissions that occur as farmers worldwide respond to higher prices and convert forest and grassland to new cropland to replace the grain (or cropland) diverted to biofuels By using a worldwide agricultural model to estimate emissions from land-use change, we found that corn-based ethanol, instead of producing a 20% savings, nearly doubles greenhouse emissions over 30 years and increases greenhouse gases for 167 years Biofuels from switchgrass, if grown on US corn lands, increase emissions by 50% This result raises concerns about large biofuel mandates and highlights the value of using waste products

We analyze the impact of trade liberalization and removal of the federal tax credit in the United States on U.S. and Brazilian ethanol markets using a multi-market international ethanol model calibrated on 2005 market data and policies. The removal of trade distortions induces a 23.9 percent increase in the price of world ethanol on average between 2006 and 2015 relative to the baseline. The U.S. domestic ethanol price decreases by 13.6 percent, which results in a 7.2 percent decline in production and a 3.8 percent increase in consumption. The lower domestic price leads to a 3.7 percent rise in the share of fuel ethanol in gasoline consumption. U.S. net ethanol imports increase by 199 percent. Brazil responds to the higher world ethanol price by increasing its production by 9.1 percent on average. Total ethanol consumption in Brazil decreases by 3.3 percent and net exports increase by 64 percent relative to the baseline. The higher ethanol price leads to a 4.9 percent increase in the share of sugarcane used in ethanol production. The removal of trade distortions and 51¢ per gallon tax credit to refiners blending ethanol induces a 16.5 percent increase in the world ethanol price.

Simla Tokgoz

Papers

Use of U.S. Croplands for Biofuels Increases Greenhouse Gases Through Emissions from Land-Use Change

Food security, farming, and climate change to 2050: challenges to 2050 and beyond

Food security, farming, and climate change to 2050: Scenarios, results, policy options

Use of U.S. Croplands for Biofuels Increases Greenhouse Gases Through Emissions from Land-Use Change

Removing Distortions in the U.S. Ethanol Market: What Does It Imply for the United States and Brazil?