CAREER: Growth of Ammonia Oxidizing Archaea and Bacteria in Semi-Arid Soils

土壤中氨氧化微生物具有重要的科学意义，因为它们的活动直接影响农业产量、水质和全球气候变化。这些微生物控制着氨转化为硝酸盐的硝化速率。这通常会导致生态系统中氮的流失，因为硝酸盐比铵更容易浸出，硝酸盐可能转化为气态的氮，包括一氧化二氮，一种强效的温室气体。氨氧化微生物很难从环境样品中分离出来，因此控制其生长的环境参数尚未确定。一种新的技术——用18o标记的水进行稳定同位素探测——已经被开发出来，它不需要培养氨氧化剂来研究它们在土壤中的生长。在这种新方法中，只有生长中的微生物的DNA被添加到土壤中的18O水标记为18O。180o标记的DNA可以从未标记的DNA中分离出来，从而可以定量标记的DNA片段中氨氧化剂特有的DNA序列的丰度。这种丰度表示氨氧化剂在土壤中的生长。氮源、温度、植物凋落物、水、pH值和土壤体积密度对氨氧化微生物生长的影响将在亚利桑那州北部的半干旱土壤中进行调查，那里的年平均降雨量在141到558毫米之间。美国原住民高中教师将获得获得微生物学研究经验的机会，以帮助他们开发有关再生水对旧金山山峰影响的课程，旧金山山峰是亚利桑那州北部许多部落的圣地。此外，与北亚利桑那大学科学教学与学习中心建立的合作关系将通过开发科学教学硕士项目的新课程得到加强。本课程将着重于如何将微生物学应用于亚利桑那州高中教学内容标准。最后，每年北亚利桑那大学的一名本科生和一名研究生将接受环境微生物学的教育，并将获得资助进行研究。

Ammonia-oxidizing microorganisms in soil are of great scientific interest because their activity directly impacts agricultural yields, water quality, and global climate change. These organisms control the rate of nitrification during which ammonia is converted to nitrate. This often results in nitrogen loss from an ecosystem, because nitrate is leached much more readily than ammonium and nitrate may be converted to gaseous forms of nitrogen, including nitrous oxide, a potent greenhouse gas. Ammonia-oxidizing microorganisms are very difficult to isolate from environmental samples and consequently the environmental parameters that control their growth have not been identified. A new technique, stable isotope probing with 18O-labeled water, has been developed that does not require cultivation of ammonia oxidizers to study their growth in soil. In this new approach the DNA of only growing microorganisms is labeled with 18O from 18O-water added to soil. The 18O-labeled DNA can be separated from non-labeled DNA so that the abundance of DNA sequences unique to ammonia-oxidizers may be quantified in the labeled DNA fraction. This abundance represents the growth of ammonia oxidizers in soil. The impact of nitrogen source, temperature, plant litter, water, pH and soil bulk density, on growth of ammonia oxidizing microorganisms will be investigated in semi-arid soils in northern Arizona, where mean annual precipitation ranges from 141 to 558 mm.This project will also encompass several important educational initiatives. Native American high school teachers will be offered opportunities to gain research experience in microbiology in order to help them develop curriculum regarding the impact of reclaimed water on the San Francisco Peaks, a sacred site to many tribes in northern Arizona. In addition, an established collaboration with the Center for Science Teaching and Learning at Northern Arizona University will be enhanced by the development of a new course in the Master of Arts in Science Teaching program. The course will focus on how microbiology can be used to teach Arizona content standards in high schools. Finally, each year an undergraduate and a graduate student at Northern Arizona University will be educated in environmental microbiology and will be funded to conduct research.