青藏高原三个盐碱湖的产甲烷菌群和产甲烷代谢途径分析

Methanogen communities and predominant methanogenic pathways in three saline-alkaline lakes on the Tibetan Plateau

摘要:

[目的] 分析青藏高原不同类型盐碱湖中的优势产甲烷菌群和优势产甲烷代谢途径。[方法] 以不同盐度和植被类型的公珠错、昆仲错和无植被的兹格塘错的沉积物为研究对象，通过高通量测序和qPCR定量古菌16S rRNA多样性分析优势古菌类群；模拟原位盐浓度及pH，比较不同产甲烷底物（甲醇、三甲胺、乙酸和H₂/CO₂）富集沉积物的产甲烷速率，分析其优势产甲烷菌代谢类型。通过添加产甲烷抑制剂（2-溴乙烷磺酸盐），检测沉积物中产甲烷底物积累，确定不同盐碱湖中主要的产甲烷途径。[结果] 昆仲错的优势菌群包括甲基/乙酸型的甲烷八叠球菌科（Methanosarcinaceae，11%），乙酸型的甲烷鬃菌科（Methanosaetaceae，7.9%）和氢型甲烷菌甲烷杆菌目（Methanomicrobiales，7.4%）；公珠错和兹格塘错的优势菌群为甲烷鬃菌科（Methanosaetaceae）分别占15%和15.3%，及甲烷杆菌属（Methanobacterium）和甲基型的甲烷叶菌属（Methanolobus）。公珠错和昆仲错分别以乙酸和甲醇产甲烷速率最高，而兹格塘错从不同底物产甲烷速率无差异。抑制甲烷产生后，公珠错主要积累乙酸，昆仲错主要积累甲醇；兹格塘错不仅甲烷排放低，也无产甲烷物质显著积累。[结论] 昆仲错沉积物中的甲烷主要来自甲醇，公珠错中的甲烷主要来自乙酸，而兹格塘错产甲烷和底物积累不活跃。因而推测高原盐碱湖主要的产甲烷途径和菌群可能与周围植被类型的相关性更高，而与盐度的直接相关性较低。

Abstract:

[Objective] To analyze the dominant methanogenic communities and methanogenic pathways in the different saline-alkaline lakes at the Qinghai-Tibet Plateau. [Methods] Using the sediments from three saline-alkaline lakes, Gongzhu Co, Kunzhong Co and Zigetang Co, that have different salinities and plantation types, as objects, we analyzed archaeal 16S rRNA diversity via high-throughput sequencing, and quantified the dominant methanogenic groups using quantitative PCR. The dominant methanogenic groups were then confirmed by comparing methane producing rates of the sediments from all known methanogenic substrates (methanol, trimethylamine, acetate and H₂/CO₂). Upon inhibition of methane production by a methanogenesis-specific inhibitor (2-bromoethanesulfonate), accumulated methanogenic precursors were determined so as to infer methanogenic pathways in the lake sediments. [Results] Methanosarcinaceae (11%), Methanosaetaceae (7.9%) and Methanomicrobiales (7.4%) were determined to be dominant in Kunzhong Co; Methanosaetaceae was accounted for 15% and 15.3% in Gongzhu Co and Zigetang Co, respectively, including the genera of Methanobacterium and Methanolobus. The highest methane production rates were determined from acetate and methanol in Gongzhu Co and Kunzhong Co respectively, but there was no difference in methane production rate from different methanogenic substrates in Zigetang Co. Methanol and acetate were respectively accumulated in methanogensis inhibited Kunzhong Co and Gongzhu Co, but no substance was obviously accumulated in Zigetang Co. [Conclusion] Methylotrophic methanogens and their implemented methanogenic pathway could be dominant in Kunzhong Co; and acetoclastic methanogens were prevalent in Gongzhu Co. However, not much methane production and substrate accumulation were determined in Zigetang Co. Based on the analysis, the dominant methanogenic pathways and methanogenic communities were predicted to be associated more with vegetation type but less with salinities of the saline-alkaline lakes on the Tibetan Plateau.