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

土壤中的氨氧化微生物具有很大的科学意义，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的氮损失，因为硝酸盐比铵更容易浸出，并且硝酸盐可以转化为气态形式的氮，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，稳定同位素探测与18 O标记的水，已经开发出来，不需要培养氨氧化剂来研究它们在土壤中的生长。在这种新的方法中，只有生长的微生物的DNA被标记为18 O-水添加到土壤中的18 O。18 O-标记的DNA可以与未标记的DNA分离，使得氨氧化剂特有的DNA序列的丰度可以在标记的DNA级分中定量。这种丰度代表了土壤中氨氧化剂的增长。氮源，温度，植物凋落物，水，pH值和土壤容重的影响，对氨氧化微生物的生长将在亚利桑那州北方，平均年降水量范围从141至558毫米的半干旱土壤进行调查。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，以帮助他们制定有关再生水对弗朗西斯科峰的影响的课程，旧金山峰是亚利桑那州北方许多部落的圣地。此外，与北方亚利桑那大学科学教学中心建立的合作将通过科学教学硕士课程的新课程的开发得到加强。该课程将重点介绍如何微生物学可以用来教亚利桑那州的内容标准在高中。最后，北方亚利桑那大学每年将有一名本科生和一名研究生接受环境微生物学教育，并将资助他们进行研究。

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.