Direct and indirect formation of organohalogens by microorganisms

有机卤素影响大气化学，从而影响地球气候。因此，有必要确定有机卤素的来源，并详细了解导致其形成的不同机制。从最近的研究中，很明显，生物（酶催化），但也涉及腐殖物质和铁矿物的非生物氧化还原反应可以导致有机卤素的形成。然而，这些过程的机制，活性有机和铁物种的身份，全球分布和地球化学参数影响酶和非生物反应，以及非生物与生物过程对全球有机卤素预算的相对贡献目前尚不清楚。该研究项目的主要目标是：i）确定铁矿物和腐殖物质的微生物氧化还原反应是否可以产生活性铁物种和腐殖化合物，从而导致挥发性有机卤素（VOX）的非生物形成; ii）量化环境中卤化酶的多样性，丰度和活性。为此，将从释放有机卤素的实地收集土壤样本。实验室微观将设置这些样品，以确定腐殖物质，铁矿物和铁/腐殖酸代谢细菌的VOX形成的作用，并评估变化的地球化学条件的影响，包括氧化还原状态，水合（水）状态和温度对VOX形成。此外，我们建议分析和量化的遗传多样性和原位基因表达的卤化酶和地球化学参数控制酶活性的缩影，在南部非洲和俄罗斯的现场。对微生物直接和间接形成有机卤素的全面了解不仅将进一步加深我们对自然生物卤化过程的理解，而且还将促进量化有机卤素化合物的来源、汇和全球负担的科学努力。

Organohalogens influence atmospheric chemistry and thereby earth climate. Thus, it is necessary to identify the sources of organohalogens and to obtain a detailed understanding of the different mechanisms that lead to their formation. From recent studies it became evident that both biotic (enzymatically catalysed), but also abiotic redox reactions involving humic substances and iron minerals can lead to the formation of organohalogens. However, the mechanisms of these processes, the identity of the reactive organic and iron species, the global distribution and geochemical parameters influencing the enzymatic and abiotic reactions, and the relative contribution of abiotic vs. biotic processes to the global organohalogen budget are currently unclear. The main goals of this research project are: i) to determine whether microbial redox reactions of iron minerals and humic substances can produce reactive iron species and humic compounds that lead to abiotic formation of volatile organohalogens (VOX) and ii) to quantify the diversity, abundance, and activity of halogenating enzymes in the environment. For this purpose soil samples from organohalogenreleasing field sites will be collected. Laboratory microcosms will be setup with these samples to determine the role of humic substances, iron minerals, and iron-/humics-metabolizing bacteria for VOX formation and to evaluate the effect of changing geochemical conditions, including redox status, hydration (water) status, and temperature on VOX formation. Further we propose to analyze and quantify the genetic diversity and in situ gene expression of halogenating enzyme and the geochemical parameters controlling enyzme activity in the microcosms and at the Southern African and Russian field sites. Comprehensive knowledge on the direct and indirect formation of organohalogens by microorganisms will not only further our understanding of natural biological halogenations processes, but also facilitate scientific efforts to quantify the sources, sinks, and global burdens of organic halogen compounds.