全球大約10-25%的甲烷來自于水稻田,。甲烷這種溫室氣體由多種微生物群（產(chǎn)烷生物）產(chǎn)生,，而位于水稻作物根部的主要產(chǎn)烷者是“水稻簇I（RC-I）Archaea”。對這些微生物而言,，氧是一種有毒物,。
這些Archaea保持其競爭優(yōu)勢的機(jī)制尚不清楚,，因?yàn)椴荒艿玫剿鼈兊募兣囵B(yǎng)物,。如今,，來自德國馬爾堡的馬克斯·普朗克學(xué)會(huì)的陸地微生物研究所和分子遺傳研究所的科學(xué)家們已經(jīng)完成了對產(chǎn)烷微生物混合培養(yǎng)體中的RC-I Archaea的基因測序。從基因序列來看,，研究人員能夠推斷出其中存在大量的酶結(jié)構(gòu),，而這些Archaea中酶之前是不為人所知的。這些酶幫助RC-I Archaea在有氧條件下生存,。它們使RC-I Archaea適應(yīng)了水稻根部周圍特殊的富氧環(huán)境,。該研究結(jié)果解釋了為何RC-I Archaea保持了其生存優(yōu)勢（結(jié)果發(fā)表在2006年7月21日出版的《科學(xué)》雜志上）。
最近的研究中,，馬普學(xué)會(huì)的研究人員研究了一種RC-I Archaeon的全部基因序列,，這種微生物經(jīng)常出現(xiàn)在MRE50混合培養(yǎng)物中。通常,，徹底分析一種微生物的基因需要純培養(yǎng)物,，這些純培養(yǎng)物具有相類似的遺傳信息。但對RC-I Archaea這種情況來說,，無法得到純培養(yǎng)物,，因此，MRE50混合培養(yǎng)體的所有遺傳信息被當(dāng)作是給整個(gè)RC-I 基因排序的基礎(chǔ),。這種來自混合培養(yǎng)物中多種不同微生物體的不同種類的遺傳信息被稱著Meta基因（Metagenome）,。分析中最主要的困難是要從Meta基因中篩選出RC-I Archaeon完整的同類基因。研究人員使用了一種特殊的生物信息學(xué)分析技術(shù)來實(shí)現(xiàn)這個(gè)目標(biāo),。
RC-I Archaeon的染色體由320萬個(gè)堿基對組成,，3103個(gè)蛋白質(zhì)編碼。其中的蛋白質(zhì)能夠根據(jù)產(chǎn)烷微生物新陳代謝的需要進(jìn)行合成,，這是為何它們只需簡單地減少二氧化碳與氫的結(jié)合就能夠生成甲烷的原因,。作為產(chǎn)烷微生物營養(yǎng)物質(zhì)的酶并非由RC-I基因編碼。因此,，RC-I Archaeon可以分為氫產(chǎn)烷微生物Archaea,，只能產(chǎn)生甲烷，當(dāng)在完全缺氧的條件下,，能量就從這里產(chǎn)生,。
通常氧的存在對它們是非常不利的。然而,，對RC-I Archaea來說并非如此，產(chǎn)烷微生物Archaea的RC-I的酶的基因代碼是獨(dú)特的,，這使其能夠在富氧環(huán)境下生存,。整組酶都屬于這種機(jī)制,。這些酶迅速分解氧活性粒子的毒性，如過氧化物陰離子,，過氧化氫物等,。這些氧活性粒子對活細(xì)胞來說毒性很重。當(dāng)存在氧的時(shí)候,，RC-I Archaea迅速切換到zymoma發(fā)酵模式,。
RC-I基因系列為研發(fā)利用分子生物學(xué)來監(jiān)測自然環(huán)境中RC-I Archaea的活動(dòng)的方法打下了基礎(chǔ)。然而,，離我們最終降低RC-I Archaea及水稻田產(chǎn)生甲烷的能力還需要多少時(shí)間還有待確定,。這個(gè)項(xiàng)目受到了馬普學(xué)會(huì)和德國聯(lián)邦教育研究部的聯(lián)合資助。
英文原文：
Sequencing The Genome Of A New Kind Of Methane Producer
About 10 to 25 percent of the world's methane emissions come from flooded rice paddies. Methane is a greenhouse gas produced by various groups of microorganisms (methanogenic Archaea). Oxygen is usually highly toxic for these microorganisms. The major producer of methane in the roots of rice plants is what is known as "Rice Cluster I" (RC-I) Archaea.
The mechanisms that give these Archaea a competitive advantage remained unexplained, because it was impossible to get a pure culture of them. Now, scientists from the Max Planck Institute for Terrestrial Microbiology in Marburg, Germany and the Max Planck Institute for Molecular Genetics in Berlin have fully sequenced the genome of an RC-I archaeon from a methane-producing microbial mixed culture. From the genome sequence, the researchers were able to deduce the existence of a number of enzymatic mechanisms, unknown in methanogenic Archaea until now. The mechanisms help the RC-I Archaea to survive when oxygen is present. They allow the RC-I Archaea to adapt specifically to the oxygen-rich area around the roots of the rice plant. The results explain why RC-I Archaea have a selective survival advantage (Science, July 21, 2006).
In the current study, Max Planck researchers from Marburg and Berlin investigated the complete genome sequence of an RC-I archaeon that appears frequently in the mixed culture MRE50. As a rule, the starting point for analysis of a complete microbial genome is a pure culture - and its corresponding homogeneous component of genetic information. But in the case of RC-I Archaea, no pure culture was available. So all the genetic information of the mixed culture MRE 50 served as the starting point for sequencing the complete RC-I genome. Such heterogeneous genetic information, stemming from various microorganisms in the mixed culture, is called a metagenome. One particular analytical challenge was filtering out the complete, homogeneous genome of a defined RC-I archaeon from the metagenome. The researchers were able to do this using a specific bio-informatics analytical methodology.
The genome of the RC-I archaeon is made from 3.2 million base pairs, and codes for 3,103 proteins. The proteins can, among other things, be organized according to their methanogenic metabolism - that is, how they create methane simply by reducing carbon dioxide with hydrogen. Enzymes for the analysis of alternative methanogenic nutrients are not encoded by the RC-I genome. The RC-I archaeon can thus be categorised as hydrogenotroph Methanogenic Archaea can only produce methane, and the energy that comes from it, when oxygen is completely absent. The presence of oxygen is normally very hostile to them. However, this is not the case for RC-I Archaea - the RC-I genome codes for enzymatic mechanisms which are unique for methanogenic Archaea and make it possible for them to survive in an oxygenated environment. A whole group of enzymes belongs to this mechanism. These enzymes quickly detoxify highly reactive oxygen species, such as superoxide anion or hydrogen peroxide. These oxygen species are extremely toxic for living cells. When oxygen is present, RC-I Archaea quickly switch to a zymoma fermentative.
Sequencing the RC-I genome offers the groundwork for developing a means of monitoring the activity of RC-I Archaea in their natural environments, using molecular biological methods. It is uncertain, however, how long it will take before we can actually reduce the methane production of RC-I Archaea - and methane emissions from places like rice paddies.
