Anaerobic quaternary amine degradation: from single bacterium to salt marsh ecosystem.

季胺（QAs）如甘氨酸甜菜碱（GBT）在海洋生物中普遍存在。由于GBT不会干扰细胞代谢，因此GBT被海洋生物用作适应环境条件变化（如盐度增加）的相容溶质。由于环境变化，例如病毒攻击和放牧，QA化合物经常被释放到海洋生态系统中。这些化合物的降解，特别是在潮间带沿海地区，对气候活性微量气体的产生作出了重大贡献。其中包括强效温室气体甲烷和挥发性甲基化胺，它们被认为与海洋环境中云的形成有关。据估计，沿海沉积物贡献了全球海洋甲烷排放量的约75%（每年8-13 Tg），其中大部分可能来自于QAs的降解。虽然我们知道微生物主要负责将GBT降解为甲烷和挥发性甲胺，但我们对降解途径中涉及的基因和酶知之甚少。此外，那些负责转化的微生物的身份尚未确定。我们目前对这两个方面的知识仍然是推测性的，至少部分原因是缺乏明确的研究。这一及时的建议旨在填补我们对海洋碳循环知识的这一重大空白。利用培养的模式微生物，我们旨在确定GBT厌氧降解的关键基因和编码酶。利用分子生态学技术和模型微生物研究的结果数据，我们的目标是进一步确定海洋环境中GBT厌氧生产甲烷和甲胺的关键微生物参与者。这项工作将产生关于我们对微生物GBT转化的理解的新知识，因此将填补我们对海洋碳循环知识的严重空白。

Quaternary amines (QAs) such as glycine betaine (GBT) are ubiquitous in marine organisms. GBT is used by marine organisms as a compatible solute in response to changes in environmental conditions, such as increasing salinity, because GBT does not interfere with cell metabolism. QA compounds are frequently released into the ocean ecosystems due to environmental changes, such as viral attack and grazing. The degradation of these compounds, especially in intertidal coastal areas, contributes significantly to the production of climate-active trace gases. These include the potent greenhouse gas methane and volatile methylated amines, which are thought to be involved in cloud formation in the marine environment. Coastal sediments are estimated to contribute approximately 75% of the global oceanic methane emissions (8-13 Tg per year) and much of this is likely to be derived from the degradation of QAs. Although we know that microorganisms are mainly responsible for the degradation of GBT to methane and volatile methylamines, we know little about the genes and enzymes involved in the degradation pathway. Furthermore, the identity of those microorganisms responsible for the transformation has not yet been determined. Our current knowledge of these two aspects remains speculative, at least partially due to the lack of definitive research.This timely proposal aims to fill in this major gap in our knowledge of marine carbon cycle. Using cultivated model microorganisms, we aim to define the key genes and the encoding enzymes in the anaerobic degradation of GBT. Using molecular ecology techniques and the resultant data from the study of the model microorganisms, we aim to further determine the key microbial players involved in the anaerobic production of methane and methylamines from GBT in the marine environment. The work will generate novel knowledge about our understanding of microbial GBT transformations and will therefore fill in a serious gap in our knowledge of the marine carbon cycle.