Distribution characteristics and controlling factors of nitrifying microorganisms in freshwater and sediment of eutrophic zones in Lake Taihu in autumn

Abstract

微生物参与下的氮循环是富营养化湖泊十分重要的生物地球化学循环过程.采用基于amoA功能基因和16S rRNA基因的荧光定量PCR、PCR-DGGE与高通量测序等分子生物学技术，调查秋季太湖不同水体和表层沉积物中氨氧化古菌（AOA）、氨氧化细菌（AOB）和亚硝酸盐氧化菌（NOB）群落丰度和组成，探讨影响硝化微生物分布的关键环境因子.结果表明，中度富营养化的梅梁湾湖区水体表层、中层和底层水样和表层底泥中AOA amoA基因的丰度分别低于轻度富营养化的湖心区，而不同层水样中AOB amoA基因的丰度分别高于湖心区.梅梁湾湖区和湖心区水样中AOA群落组成基本相似，2个湖区表层沉积物样品中AOA群落组成亦基本相似，水体中AOA群落组成与表层沉积物中AOA群落组成有差异，AOA群落丰度显著受硝态氮、pH和DO影响；表层沉积物中AOB群落丰度有明显差异且显著受总氮含量影响，表层沉积物中NOB群落丰度也有明显差异且显著受亚硝态氮含量影响.太湖梅梁湾湖区和湖心区水体与表层沉积物AOA群落包括Nitrosopumilium和Nitrosotalea两大属；表层沉积物AOB群落主要包括亚硝化单胞菌（Nitrosomonas）和亚硝化螺菌（Nitrosospira）两大属，NOB群落主要包括硝化刺菌（Nitrospina）和硝化螺菌（Nitrospira）两大属，其中硝化螺菌属是淡水湖泊中比较少见的亚硝酸盐氧化菌.影响太湖水体和沉积物中AOA和AOB丰度的最主要环境因子为总氮、总磷与铵态氮.研究表明典型富营养指标（总氮、总磷、铵态氮、硝态氮和硝态氮等）是影响太湖梅梁湾和湖心区水体和沉积物中AOA或AOB丰度以及硝化微生物群落丰度的重要因素.;Nitrogen cycling associated with microorganisms is the most important biogeochemical process in eutrophic lakes. In this study, molecular biological techniques including quantitative PCR, PCR-DGGE, and high-throughput sequencing based on amoA and 16S rRNA genes were used to assess the composition and community abundance of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB) in freshwater and sediment samples of Lake Taihu collected during autumn. The key environmental factors affecting the distribution of nitrifying microorganisms were further analyzed. Results showed that the amoA gene abundance of AOA from the upper, middle, and bottom freshwater and surface sediment samples from the mesotrophic Meiliang Bay was lower than those from the less eutrophic central lake and that the amoA gene abundance of AOB from the mesotrophic Meiliang Bay was greater than those from the central lake. The AOA community composition in freshwater was similar in both Meiliang Bay and the central lake, it was the same for AOA in the surface sediment, and the key factors affecting AOA community abundance were nitrate, pH and dissolved oxygen contents, while the community abundance of AOB mainly affected by total nitrogen content in sediments were proven to differ considerably between the two sites. The case was the same for NOB with the key factor nitrite content. AOA of freshwater and surface sediments in Meiliang Bay and central lake included two genera, Nitrosopumilis and Nitrosotalea. AOB of the surface sediment included Nitrosomonas and Nitrosospira. NOB of the surface sediment included Nitrospina and Nitrospira, and Nitrospina was scarce in freshwater. The main environmental factors affecting the abundance of AOA and AOB in Lake Taihu were TN, total phosphorus (TP), and ammonium content. This study proved that the eutrophication indexes (such as total nitrogen, total phosphorus, ammonium, nitrate and nitrite) have significant influences on the abundance of AOA or AOB and community abundance of nitrifying microorganisms in both freshwater and sediments in Lake Taihu, which may help the understanding of the nitrogen cycling in the Lake Taihu ecosystem.