The tree phyllosphere microbiome - an overlooked and important sink for carbon monoxide?

在这个项目中，我们将调查与树木地上部分相关的微生物是否是重要的一氧化碳气体降解剂。一氧化碳（CO）是不完全燃烧过程的产物，并且被大多数人认为是潜在的致命气体和空气污染的成分。然而，它也是一种天然存在的痕量气体，由自然环境过程产生，其背景大气浓度仅为十亿分之50-150。即使在大气中的这些痕量水平，CO是无毒的，这种气体也起着重要的作用，因为它影响其他大气气体的寿命。它被认为是一种短暂的气候强迫因素和间接的温室气体。这是由于它与羟基（OH）自由基反应，这对各种大气痕量气体的反应很重要，其中一些有助于温室效应，如甲烷和对流层臭氧。因此，大气中CO水平的升高会对气候产生间接影响，因为它会消除OH自由基，否则OH自由基可能会与甲烷和臭氧发生反应，从而增加这些重要温室气体的寿命和影响。此外，CO在较高浓度时会影响空气质量和人类健康。特定微生物降解CO的能力早已为人所知，先前的研究已经确定，土壤和海洋中存在CO降解微生物。通过降解CO，这些微生物有助于CO的自然循环，并将其从大气中去除或防止其从土壤和海水中排放到大气中，从而有助于调节其天然低浓度。我们最近发现，树木的地上部分被CO降解微生物定殖。在全球范围内，树木的叶圈是微生物的广阔栖息地，因此叶圈中的微生物活动也具有全球重要性。栖息在叶际（主要是叶和茎）的微生物与大气直接接触，因此能够吸收活植物组织中光化学反应产生的CO或从周围空气中吸收CO。它们的CO降解活性以前没有被证明。只有在我们以前的工作中与树叶相关的CO降解微生物的CO降解的潜力已被证明;这些发现值得进一步调查，因为这意味着一个潜在的主要全球CO去除机制尚未被确认以前。了解这一过程是非常重要的，因为它将允许解开如何在叶际的CO降解微生物影响CO从植被通量。确定叶际CO降解微生物的多样性，了解它们中哪些是活性的，以及它们的活性如何受到环境因素的影响，对于更好地理解来自植被的CO通量如何受到调节以及它们如何在时间和空间尺度上变化至关重要。在培养实验中，我们将能够确定环境浓度下的CO降解，然后利用基于叶际微生物DNA和RNA测序的现代宏基因组学和元转录组学方法分别鉴定和鉴定这些CO降解微生物。因此，我们工作的见解将为全球CO循环提供基本的新见解，并有助于更好地了解微生物活动如何影响大气的组成。它还将使我们能够研究CO降解微生物如何从根本上影响大气化学和植被的CO排放，这是一个影响全球气候的过程。

In this project, we will investigate whether microorganisms associated with the above ground parts of trees are important as degraders of the gas carbon monoxide. Carbon monoxide, CO, is a product of incomplete combustion processes and is known to most people as a potentially lethal gas and component of air pollution. However, it is also a naturally occurring trace gas that is produced by natural environmental processes which contribute to its background atmospheric concentration of just 50-150 parts per billion. Even at these trace levels in the atmosphere, at which CO is not toxic, this gas plays an important role because it affects the lifetime of other atmospheric gases. It is referred to as a short-lived climate forcer and an indirect greenhouse gas. This is due to it reacting with hydroxyl (OH) radicals which are important for reactions of a wide range of atmospheric trace gases, some of which contribute to the greenhouse effect such as methane and tropospheric ozone. Elevated levels of CO in the atmosphere therefore have an indirect impact on climate, by removing OH radicals which could otherwise react with methane and ozone, thereby increasing the lifetime and effect that these important greenhouse gases have. In addition, CO affects air quality and human health at higher concentrations.The ability of specific microorganisms to degrade CO has long been known, and previous studies have established that CO degrading microorganisms are present in soils and in the oceans. By degrading CO, these microorganisms contribute to the natural cycling of CO and either remove it from the atmosphere or prevent it from being emitted to the atmosphere from soils and seawater, thus contributing to regulating its natural low concentrations. We have recently shown that the above ground parts of trees are colonised by CO degrading microorganisms. At the global scale, the phyllosphere of trees is a vast habitat for microorganisms, microbial activities in the phyllosphere are therefore also of global importance. Microorganisms inhabiting the phyllosphere (primarily the leaves and stems) are in direct contact with the atmosphere and are therefore able to take up CO produced by photochemical reactions in live plant tissue or take it up from the surrounding air. Their CO degradation activity has not been shown previously. Only in our previous work on CO-degrading microorganisms associated with tree leaves has the potential of CO degradation been shown; these findings warrant further investigation because it means that a potentially major global removal mechanism for CO has not been recognised previously. Understanding this process is fundamentally important because it will allow to disentangle how CO-degrading microorganisms in the phyllosphere affect CO fluxes from vegetation. Identifying the diversity of phyllosphere CO-degrading microorganisms, understanding which of them are active, and how their activity is affected by environmental factors is vital to provide a better comprehension of how the CO-fluxes from vegetation are regulated and how they vary across temporal and spatial scales.In incubation experiments, we will be able to determine degradation of CO at environmental concentrations, and then identify and characterise these CO-degrading microorganisms using modern metagenomic and metatranscriptomics approaches which are based on the sequencing of the DNA and RNA of the phyllosphere microorganisms, respectively. The insights from our work will thus provide fundamental new insights into the global cycle of CO and contribute to a better understanding of how the composition of the atmosphere is affected by microbial activities. It will also allow us to examine how CO degrading microorganisms fundamentally affect atmospheric chemistry and CO emission from vegetation, a process that affects global climate.