Impact of microorganisms as sinks of atmospheric chloromethane

一个由两个法国合作伙伴和两个德国合作伙伴组成的跨学科联盟将结合他们的专业知识，解决微生物对全球氯甲烷(CH3Cl)预算的影响。自1989年《蒙特利尔议定书》生效以来，人类活动造成的臭氧消耗化合物(CFCs)排放量大幅减少。因此，从自然来源释放的化合物，如CH3Cl，在平流层臭氧消耗中变得越来越重要。这种氯化气体是大气中含量最丰富的卤化化合物，其主要来源是陆地生态系统。从活的和死的植物中释放的物质和生物质燃烧是主要的来源。对温度的正线性响应表明，未来气候变暖可能会导致CH3Cl排放增加。然而，目前对CH3Cl全球预算的估计是不确定的，表明微生物在降解大气CH3Cl方面发挥的作用比之前认为的更重要。甲基营养微生物存在于土壤中，许多植物的叶圈中都有这种微生物，其中一些具有降解CH3Cl的代谢能力，最近有报道称它们在云层的水滴中活动。申请者设想，拟议项目的主要目标是揭示过程一级的定量信息，并提供对这些微生物的深入遗传洞察。该联盟将研究与土壤、植物和云相关的甲基营养菌降解CH3Cl过程中的动力学和同位素效应。将进行特定CH3Cl降解亚甲基营养菌的实验室实验，以测量它们对同位素组成的影响，并确定温度对动力学参数的影响。在不同的环境样品中，微生物群落将通过使用分类学(16S RNA基因)和CH3Cl降解功能基因标记物(CmuA)的扩增靶向下一代测序来表征。选定的土壤、植物和云水样品将受到CH3Cl的13C-等位拓扑学的影响，以标记CH3Cl转化微生物的生物量。然后将使用DNA稳定同位素探测、全基因组扩增和MiSeq(Illumina)高通量测序的组合来检索元基因组。这些实验将评估微生物降解CH3Cl途径的多样性，并将有助于发现新的甲基转移酶和进一步参与CH3Cl代谢转化的基因。元基因组学方法将为温带陆地生态系统和云中降解CH3Cl的微生物群落提供新的见解。动力学和同位素数据将确定微生物汇与全球CH3Cl预算的数量相关性。改进对大气中CH3Cl源和汇的定量了解，对于提高我们对平流层氯化学和臭氧层稳定性的预测能力将是非常宝贵的。

An interdisciplinary consortium of two French and two German partners will combine their expertise and knowledge to address the impact of microorganisms on the global budget of chloromethane (CH3Cl). Anthropogenic emissions of ozone depleting compounds (CFcs) have been strongly reduced since the Montreal protocol came into force in 1989. As a consequence, compounds released from natural sources, such as CH3Cl, have become increasingly relevant in stratospheric ozone depletion. This chlorinated gas is the most abundant halogenated compound in the atmosphere whose primarily source is the terrestrial ecosystems. Release from living and dead vegetation and biomass burning are major sources. The positive linear response with temperature suggests that future warmer climates will likely lead to increased CH3Cl emissions. However, current estimates of the CH3Cl global budget are uncertain and suggest that microorganisms play a more important role in degrading atmospheric CH3Cl than previously thought. Methylotrophic microbes, some with the metabolic capability to degrade CH3Cl, occur in soils, the phyllosphere of many plants, and have recently been reported to be active in water droplets of clouds. The applicants conceive that the main objectives of the proposed project are to reveal quantitative information on process-level and to provide in depth genetic insights into these microbes. The consortium will investigate kinetic and isotope effects during CH3Cl degradation by methylotrophs associated with soils, plants, and clouds. Laboratory experiments with specific CH3Cl degrading methylotrophs will be conducted to measure their effects on isotope composition and to determine temperature effects on kinetic parameters. In various environmental samples the microbial community will be characterized using amplicon-targeted next generation sequencing employing a taxonomical (16S RNA genes) and a functional gene marker for CH3Cl degradation (cmuA). Selected samples of soil, plants, and cloud water will be subjected to 13C-isoptopologue of CH3Cl in order to label the biomass of CH3Cl converting microbes. Metagenomes will then be retrieved using a combination of DNA stable isotope probing, whole genome amplification, and MiSeq (Illumina) high throughput sequencing. These experiments will assess the diversity of the microbial CH3Cl-degrading pathways, and will enable the discovery of novel methyltransferases and further genes involved in CH3Cl metabolic transformation. The metagenomic approach will provide new insights into CH3Cl-degrading microbial communities of temperate terrestrial ecosystems and clouds. Kinetic and isotopic data will resolve the quantitative relevance of microbial sinks for the global CH3Cl budget. A improved quantitative understanding of the sources and sinks of atmospheric CH3Cl will be invaluable for enhancing our predictive capability for stratospheric chlorine chemistry and ozone layer stability.