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

土壤中氨氧化微生物的活动直接影响农业产量、水质和全球气候变化，因此具有重要的科学意义。这些生物控制着硝化作用的速率，在这个过程中，氨被转化为硝酸盐。这通常会导致生态系统的氮素流失，因为硝酸盐比铵更容易淋溶，硝酸盐可能会转化为气态氮，包括一种强有力的温室气体--一氧化二氮。氨氧化微生物很难从环境样本中分离出来，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，不需要培养氨氧化菌来研究它们在土壤中的生长。在这种新的方法中，只生长微生物的DNA被标记为18O-加入土壤中的18O-水。18O标记的DNA可以从非标记的DNA中分离出来，从而可以在标记的DNA组分中定量测定氨氧化菌特有的DNA序列的丰度。这种丰度代表了土壤中氨氧化剂的生长。在亚利桑那州北部年平均降雨量为141至558毫米的半干旱土壤中，将研究氮源、温度、植物凋落物、水、pH和土壤容重对氨氧化微生物生长的影响。该项目还将包括几个重要的教育举措。美国原住民高中教师将有机会获得微生物学方面的研究经验，以帮助他们制定关于再生水对旧金山峰影响的课程，旧金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和学习中心已建立的合作将通过开发科学硕士教学计划中的一门新课程来加强。这门课程的重点将是如何利用微生物学在高中教授亚利桑那州的内容标准。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方面的教育，并将获得资金进行研究。

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.