桂林会仙岩溶湿地产甲烷菌的数量、群落组成和活性

Methanogenic community structure, abundance, and activity in Huixian karst wetland, Guilin, China

甲烷产生过程是湿地生态系统中最活跃的生物地球化学进程之一,岩溶湿地是一类具有典型岩溶地区水文特征和重要环境影响的特殊内陆淡水湿地.为了解岩溶湿地产甲烷菌的类型及其在碳循环中的贡献,综合运用分子生物学、微生物学和地球化学的方法对桂林会仙岩溶湿地沉积物中产甲烷菌的数量、群落组成、活性以及相关的环境因子进行研究.分析15-35 cm沉积物中甲基辅酶M还原酶基因mcr A的数量、种类以及与环境因子之间的关系,发现mcr A基因的拷贝数为106^(-1)07,主要来自5类产甲烷古菌目,分别是甲烷微菌目(Methanomicrobiales)、甲烷八叠球菌目(Methanosarcinales)、甲烷胞菌目(Methanocellales)、甲烷杆菌目(Methanobacteriales)以及一类尚未鉴定的产甲烷古菌,这些序列中有一半的序列与已知Mcr A蛋白序列相似度在95%以下,并且mcr A基因的多样性和数量分布主要受到有机碳和硫酸盐含量的影响.在产甲烷活性方面,沉积物的乙酸型产甲烷速率为1 024(±447)pmol g~(^(-1)) d^(-1),氢型产甲烷量约为650(±155)pmol g~(^(-1)) d^(-1).上述结果表明,会仙岩溶湿地具有同普通淡水湿地类似的产甲烷菌群落组成和较高的产甲烷潜力,并且该环境中可能蕴藏着许多尚未被研究的微生物资源.

Microbial methanogenesis is one of the active biogeochemical processes that occur in wetland environments. Karst wetlands are a type of freshwater wetland with environmental relevance and special hydrographic features. However, microbial methanogenesis in karst wetlands has been underappreciated. In order to understand the composition and environmental roles of methanogens in Huixian karst wetland, Guilin, southern China, the activity and vertical distribution of methanogenic communities were studied, as well as their correlations with selected environmental factors. Analysis of the 15-35 cm depth sediment layers indicated that methyl coenzyme reductase A （mcrA） gene copies ranged from 106 to 107 per gram. The dominant methanogens were Methanomicrobiales, Methanosarcinales, Methanocellales, and a group of uncharacterized methanogens. Fifty-one percent of the sequences in this study shared less than 95% identity with known mcrA sequences. The diversity and abundance of the mcrA gene correlated closely with organic carbon and sulfate concentrations in the sediment. The potential CH4 production from acetate and hydrogen was 1 024 （± 447） pmol g-1 d-1 and 650 （± 155） pmol g-1 d-1, respectively. The results show that Huixian karst wetland contained similar methanogens to other freshwater wetlands, and these had considerable potential to produce methane. The wetland could be a rich source of unstudied microbes.