珠江口好氧不产氧光合细菌的分布、多样性及其调控机制研究

Aerobic anoxygenic phototrophic bacteria (AAPB) obligate aerobic microorganisms utilizing light energy via photosynthetic reaction centres composed of bacteriochlorophyll a. In contrast to oxygenic or anaerobic anoxygenic phototrophs, they are incapable of autotrophic CO2 fixation and require supply of organic carbon substrates. They are thought to be important players in carbon cycling in the ocean and enough to alter a marine region from a sink to a source of atmospheric CO2. In spite of an increasing body of information regarding AAPB in the marine environment,only little is known about the diversity and biogeography of AAPB in particle-rich, turbid estuaries. With light energy as a supplement to organic carbon respiration, it was suggested that AAPB would be most abundant in the oligotrophic water, where organic matter is low. However,observations by different investigators and from different locations do not agree with each other to date regarding the general distribution patterns of AAPB. So we assumed that trophic levels only explained a part of abundance and diversity of AAPB. This conflict among observations suggests that the controlling mechanisms are more complex than previously thought. We suggest that salinity and sediment resuspension may played a key role in diversity and community composition of AAPB in Pearl River Estuary. To explore questions regarding the controls of these photoheterotrophic bacteria, we examined their abundance by epifluorescence microscopy, concentrations of the light-harvesting pigment, bacteriochlorophyll a (BChl a) and the diversity of pufM and 16S ribosomal RNA (rRNA) genes in Pearl River Estuary. The reaserch is not only enrich the biogeography of microorganism, but also provide the framework for estimating the carbon flux and it is very important to announce the carbon sink or source in estuarine and coastal areas.

好氧不产氧光合细菌(AAPB)能利用光能从而减少了对有机碳的呼吸消耗，在海洋碳循环中有重要作用，对海洋碳的"汇""源"格局有重要影响。我们前期研究发现珠江 河口地区好氧不产氧光合细菌分布广泛，并且有明显的时空变化差异。但是对于河口水环境 中好氧不产氧光合细菌的多样性及其调控机制等认识还十分有限。我们提出假设在珠江河口 地区营养水平可能仅仅解释了一部分 AAPB 多样性和丰度变化规律，盐度和沉积物再悬浮对 珠江河口 AAPB 的分布、多样性、丰度、时空变化规律有重要影响。我们拟采用分子生态学 研究方法对 AAPB 生物地理学问题进行研究，通过野外调查和围隔实验证明营养盐水平、盐 度和沉积物再悬浮对 AAPB 多样性和群落结构的影响，阐明 AAPB 在珠江河口的分布格局及其生态学机制。研究成果不仅丰富了微生物的生物地理学理论，对揭示边缘海河口地区碳的"汇""源"格局也有重要启示意义。

好氧不产氧光合细菌(Aerobic anoxygenic phototrophic bacteria, AAPB)是一类具有光合作用能力的异养细菌，在水体碳循环中起重要作用，目前国内外关于河口地区AAPB的多样性及群落结构研究较少。本项目以pufM基因为分子标记物构建克隆文库，研究珠江河口不同营养盐、盐度等环境梯度下AAPB多样性及群落结构的研究，揭示影响其主要环境因子。结果显示好氧不产氧光合细菌在珠江口富营养水体中广泛分布，丰富了我们对富营养化河口水体中好氧不产氧光合细菌的认识。在0.09-33.80ppt盐度梯度范围内，分析AAPB系统多样性（phylogenetic diversity）、Shannon-Weaver指数、Simpson指数、Chao指数和操作分类单元数量的多样性估算所获得的AAPB多样性均表现出明显的盐度梯度变化。从低盐度到高盐度梯度AAPB多样性表现出现升高，到盐度为20ppt左右再降低的一个规律。从营养水平来看，在我们调查的珠江口区域AAPB多样性随着DIN、Chla的升高而升高；和DIP没有表现出明细的梯度变化趋势。AAPB多样性和DOC是负相关的关系。珠江河口优势AAPB主要为Rhodobacter-like、Erythrobacter-like、Rubrivivax-like、Loktanella-like、Rosebacter-like、Sphingomonas-like、Rubritepida-like、Erythrobacter-like等类群。对AAPB相对组成与其他环境因子的关系分析，统计结果发现水体的DIN、DOC等营养物质浓度具有显著关系，珠江河口水体中DIN、DOC等物质的浓度增加，Rhodobacter-like、Rhodobacter-like、Erythrobacter-like、Sphingomonas-like、Rubrivivax-like、Loktanella-like等类群AAPB相对数量总体上呈现增加的趋势。总体上在调查的珠江口区域，AAPB的阿尔法多样性随着营养盐（特别是DIN）梯度有明显影响，随着营养盐的增加AAPB多样性增加。AAPB多样性对DIP和DOC响应不明显。