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由于气候变化影响自然环境和人类文明,温室气体的研究受到广泛关注[1-2]。CH4排放后20年尺度内增温效应是CO2的84倍[3]。因此,CH4比CO2具有更强的温室效应。2023年4月,美国国家海洋和大气管理局(NOAA)监测数据显示CH4浓度已经达到1.37 mg·m3且未来将持续增长,而湿地CH4排放量占全球总量的20%~39%[4],湿地中植物根系代谢物或植物残体会转变成产甲烷微生物的底物,为CH4的产生创造有利条件[5]。因此,控制湿地CH4排放对减缓全球气候变暖至关重要。
生物氧化是抵消CH4产生的一个关键过程,其中甲烷氧化菌对氧化CH4有主导作用[6]。为进一步了解甲烷氧化菌对湿地CH4减排的贡献,各地学者对甲烷氧化菌进行了系列研究,在微生物群落多样性、丰度及分布特征方面取得阶段性进步。YANG等[7]发现滇池淡水湖中甲烷氧化菌群主要由甲基球菌(Methylococcus)、甲基杆菌(Methylobacter)和甲基弯曲菌(Methylosinus)组成,而Type Ⅰ型甲烷氧化菌的数量通常多于Type II型。邓永翠团队自2013年开始研究青藏高原地区土壤微生物群落组成[8],表明优势甲烷氧化菌群是甲基杆菌和甲基孢囊菌(Methylocystis),但它们的分布会受到环境因素差异的影响[9]。而铁是地球上含量第四丰富的元素,并且普遍存在于湖泊沉积物中,但针对于富铁环境中甲烷氧化菌的群落结构及关键驱动因素的研究还鲜见报道。此外,研究表明在缺少氧分子的情况下甲烷氧化菌可以利用铁、锰等作为电子受体[10],ETTWIG等[11]通过使用13C标记甲烷进行批量培养,证明了可溶性铁Fe(Ⅲ)可作为电子受体支撑CH4氧化活性,并且将之前发现的依赖铁的甲烷厌氧氧化过程与在许多湿地检测到的微生物联系起来,很好地解释了铁和甲烷生物循环之间的相互作用。但细胞不能直接利用氧化铁将通过胞外电子传递途径生物还原氧化铁,如导电毛(e-pili)、多血红素细胞色素(MHCs)和电子穿梭[12]。ELUL等[13]研究表明微生物群落可能通过多血红素c型细胞色素或微生物纳米导线(Microbial nanowires)将电子直接转移到细胞外矿物质。LI等[14]认为甲烷氧化菌将甲烷转化为乙酸等低分子量有机物时会分泌电子穿梭体,可以将胞内的电子传递到胞外被胞外的Fe(III)接受。然而,利用铁离子作为甲烷氧化菌的替代电子受体的微生物机制及其生态贡献尚不明确。但已有研究证明甲烷氧化菌能够将CH4转化成CO2或者同化为细胞生物量[15],氧化沉积物中产生的90%甲烷[16]。因此,利用甲烷氧化菌治理散排甲烷无非是一种潜在的绿色方案。
本研究以牟尼沟草海湿地为研究对象,基于高通量测序技术对湿地中甲烷氧化菌的群落特征进行研究,结合关键环境驱动因素分析和功能预测分析,进一步讨论了草海湿地中甲烷氧化菌群落结构及其功能代谢特性。并从中筛选出一株代表性甲烷氧化菌,探究了该菌株在富铁溶液中铁离子变化趋势、胞外产物分析及对甲烷的氧化效率,为湿地甲烷减排提供参考。
富铁环境中甲烷氧化菌群落结构与甲烷氧化特性
Community structure and methane oxidation characteristics of methanotrophs in iron-rich environment
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摘要: 近年来湿地潜在甲烷排放备受关注,牟尼沟草海富铁湿地具有十分重要的生态地位,而目前有关该区域甲烷氧化菌群落结构与氧化特性的研究相对较少。通过第二代高通量测序技术探究了草海富铁湿地中甲烷氧化菌的群落结构及功能并从中筛选出一株优势甲烷氧化菌在富铁溶液中进行实验探究。测序结果表明,优势甲烷氧化菌为Type Ⅰ型的甲基杆菌(Methylobacter)和甲基单胞菌(Methylomonas),RDA分析结果表明,pH和ORP是影响甲烷氧化菌群落的关键环境驱动因素。结果表明,反应过程中菌株会分泌腐殖质等产物将胞内电子转移到胞外,使溶液中的Fe(Ⅲ)作为电子受体。并且在富铁溶液中甲烷氧化效率提高了10.8%左右,7 d内菌株能够完全氧化瓶内的甲烷气体。以上结果以期为湿地甲烷减排提供理论参考依据。Abstract: In recent years, the potential methane emission from wetlands has attracted much attention. The iron-rich wetland in Caohai of Munigou has a very important ecological status. However, there are relatively few studies on the community structure and oxidation properties of methanotrophs in this area. The next generation sequencing technology was used to study the community structure and function of methanotrophs in the iron-rich wetland of Caohai, and a type of dominant methanotrophs was screened out to conduct experiment tests in the iron-rich solution. Sequencing results showed that the dominant methanotrophs were Type I Methylobacter and Methylomonas, and RDA analysis indicated that pH and ORP were the key environmental drivers affecting the methanotrophs community. The experimental results showed that during the reaction, the strain could secrete products like humus to transfer intracellular electrons to extracellular ones. Therefore, Fe (Ⅲ) in the solution could act as an electron acceptor. The oxidation efficiency of methane in the iron-rich solution increased by about 10.8%, and the strain could completely oxidize the methane gas in the flask within 7 days. These results are expected to provide a theoretical reference for methane emission reduction in wetlands.
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Key words:
- iron-rich wetland /
- methanotrophs /
- community structure /
- methane oxidation
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表 1 草海湿地上覆水及沉积物的理化性质
Table 1. Physical and chemical properties of overlying water and sediments in Caohai wetland
名称 上覆水 沉积物 pH ORP/
mVNO3−/
(mg·L−1)SO42−/
(mg·L−1)TN/
(mg·L−1)TP/
(mg·L−1)TOC/
(mg·g−1)Fe/
(mg·g−1)Mn/
(mg·g−1)CH1-1 7.86 165.4 1.394 4.422 1.851 0.505 177.9 166.947 1.332 CH1-2 7.86 170.7 1.385 4.157 1.839 0.505 182.6 169.350 1.358 CH1-3 7.89 164.7 1.351 4.319 1.891 0.649 198.7 163.379 1.626 CH2-1 7.57 176.3 1.377 6.883 1.927 1.083 155.8 157.106 0.977 CH2-2 7.58 178.3 1.336 6.557 1.950 0.794 148.6 155.136 0.913 CH2-3 7.85 170.7 1.348 6.799 1.887 1.083 153.6 155.473 0.881 CH3-1 7.82 167.9 1.425 7.043 1.945 0.733 166.6 186.450 0.891 CH3-2 7.85 169.0 1.411 6.886 1.915 0.777 183.7 180.468 0.899 CH3-3 7.85 171.7 1.409 7.079 1.952 0.794 173.9 170.401 0.810 -
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