Collaborative Research: What Limits Denitrification and Bacterial Growth in Lake Bonney, Taylor Valley, Antarctica?

反硝化作用是生态系统中固定氮流失的主要过程，对这一过程的调控可能在短期和长期尺度上直接影响初级生产和碳循环。此前关于生物活性金属在调节南极洲东部泰勒河谷永久冰盖的邦尼湖细菌反硝化作用的研究表明，反硝化细菌可受到铜、铁、镉、铅、铬、镍、银和锌等金属的负面影响；并且该湖东西叶的反硝化活性存在明显差异。研究发现，低铁浓度会加剧其他金属的潜在毒性，而银具有特异性抑制反硝化作用的潜力，因为它能够干扰亚硝酸盐还原酶和一氧化二氮还原酶等氧化还原蛋白中的铜结合。高银浓度可能会阻止一氧化二氮还原酶的功能，就像简单的铜限制一样，从而导致一氧化二氮的积聚，并导致一个不起作用的氮循环。其他因素，如氧气浓度，也可能影响邦尼湖的细菌活动。本项目将调查银毒性、一般金属毒性和氧气浓度，以确定它们对湖泊反硝化的影响，方法是使用一套在邦尼湖水中培养并经过各种处理的反硝化细菌(从湖泊中分离出来)。这些菌株对金属和氧气浓度变化的生理反应将通过单细胞分子探针的流式细胞仪检测来量化，该探针的灵敏度和解释已经针对前哨菌株进行了优化。了解金属和反硝化作用之间的关系有望增强我们不仅对邦尼湖异常的氮循环，而且更广泛地了解金属在调节微生物氮转化中的潜在作用。这项工作的更广泛影响不仅包括更好地了解区域生物地球化学和对这些过程的全球视角；而且还包括对研究生的培训和对学童的实质性宣传努力。

Denitrification is the main process by which fixed nitrogen is lost from ecosystems and the regulation of this process may directly affect primary production and carbon cycling over short and long time scales. Previous investigations of the role of bioactive metals in regulating denitrification in bacteria from permanently ice-covered Lake Bonney in the Taylor Valley of East Antarctica indicated that denitrifying bacteria can be negatively affected by metals such as copper, iron, cadmium, lead, chromium, nickel, silver and zinc; and that there is a distinct difference in denitrifying activity between the east and west lobes of the lake. Low iron concentrations were found to exacerbate the potential toxicity of the other metals, while silver has the potential to specifically inhibit denitrification because of its ability to interfere with copper binding in redox proteins, such as nitrite reductase and nitrous oxide reductase. High silver concentrations might prevent the functioning of nitrous oxide reductase in the same way that simple copper limitation does, thereby causing the buildup of nitrous oxide and resulting in a nonfunctional nitrogen cycle. Other factors, such as oxygen concentration, are likely also to affect bacterial activity in Lake Bonney. This project will investigate silver toxicity, general metal toxicity and oxygen concentration to determine their effect on denitrification in the lake by using a suite of "sentinel" strains of denitrifying bacteria (isolated from the lake) incubated in Lake Bonney water and subjected to various treatments. The physiological responses of these strains to changes in metal and oxygen concentration will be quantified by flow cytometric detection of single cell molecular probes whose sensitivity and interpretation have been optimized for the sentinel strains. Understanding the relationships between metals and denitrification is expected to enhance our understanding of not only Lake Bonney's unusual nitrogen cycle, but more generally, of the potential role of metals in the regulation of microbial nitrogen transformations.The broader impacts of this work include not only a better understanding of regional biogeochemistry and global perspectives on these processes; but also the training of graduate students and a substantial outreach effort for school children.