象山港网箱养殖区与非养殖区的细菌群落分布

近海集约化养殖是导致我国近海污染的主要来源之一。浮游细菌在近海生态系统的物质循环过程中发挥重要作用,研究海洋浮游细菌群落对养殖活动的响应,对于指示和评价海水养殖生态系统健康具有重要意义。采集了象山港网箱养殖区与非养殖区3个深度,包括表层(0.5 m)、中层(2.5 m)、底层(8.0 m)的水样,利用焦磷酸测序技术测定16S rRNA基因,研究浮游细菌的群落结构和多样性。结果表明:网箱养殖活动不仅使得附近区域水体理化性质发生改变,如化学需氧量浓度显著高于非养殖区域,而且显著地(P0.05)改变了浮游细菌的群落结构,但不同深度间群落结构和多样性的差异不显著。网箱养殖区和非养殖区中主要浮游细菌类群为α-变形菌(Alphaproteobacteria)、γ-变形菌(Gammaproteobacteria)、拟杆菌(Bacteroidetes)、放线菌(Actinobacteria)、β-变形菌(Betaproteobacteria)、ε-变形菌(Epsilonproteobacteria)和其它变形菌(Unclassified Proteobacteria),占细菌总序列数的98.64%。有些细菌类群的平均相对丰度从网箱区到非养殖区差异显著,如拟杆菌(P0.01)和放线菌(P0.05)显著降低,而γ-变形菌(P0.05)显著增加。相似度分析表明γ-变形菌、α-变形菌和拟杆菌是造成网箱区和非养殖区群落差异的主要类群,对群落差异总贡献率达到45.02%。偏冗余分析表明,影响细菌群落分布的主要环境因子有化学需氧量、磷酸盐、铵盐和总有机碳,共解释38.18%的群落变异,空间距离单独解释10.66%的群落变异。实验结果表明,养殖活动导致浮游细菌群落的改变,其中拟杆菌、放线菌和γ-变形菌的丰度显著变化,可能用于评价养殖水体的水质状况。

Distribution of bacterioplankton communities in cage culture and non-cultured areas of Xiangshan Bay, Ningbo, China

Intensive aquaculture has been a major source of coastal pollution. Microorganisms play a critical role in primary production and biogeochemical processes such as substance cycling and energy transformation in coastal ecosystems. Bacterioplankton are considered to be a dominant group because of their many contributions to ecosystem functional processes. Studying the influences of aquaculture activities on bacterial diversity in water is significant for assessing the structure and function of mariculture ecosystems. Xiangshan Bay, an important mariculture base located in Ningbo, China, is subject to a large influx of organic matter from the rapid development of aquaculture. Thus, understanding the responsive pattern of the bacterioplankton community to aquaculture sheds light on indicating and evaluating the health status of the mariculture ecosystem. In this study, water samples were collected separately from three depths: the surface, middle, and bottom levels of the water column (corresponding to 0.5, 2.5, and 8.0 m below the water surface, respectively), from a cage culture area and a non-cultured area in Xiangshan Bay, on April 10, 2012. Using the 16S rRNA gene amplicon pyrosequencing technique, we evaluated the effects of aquaculture activities on variations within bacterioplankton communities. The results showed that cage aquaculture dramatically changed the geochemical variables of water. For example, there was a substantial increase of chemical oxygen demand in the culture area. In addition, cage aquaculture significantly (P < 0.05) altered the bacterioplankton community structure, although the alpha diversity was not affected. The bacterioplankton communities were very similar across the three water depths, dominated by Alphaproteobacteria, Gammaproteobacteria, Bacteroidetes, Actinobacteria, Betaproteobacteria, Epsilonproteobacteria, and Unclassified Proteobacteria, accounting for 98.64% of the total bacteria. The relative abundances of some dominant phyla were considerably different between the two investigated areas. For example, the relative abundances of Bacteroidetes and Actinobacteria were significantly lower in the non-cultured area than in the cage culture area, while that of Gammaproteobacteria was significantly higher in the non-cultured area. Similarity percentage (SIMPER) analysis further indicated that the presence of Gammaproteobacteria, Alphaproteobacteria, and Bacteroidetes taxa controlled the differences in bacterial communities between the two areas, which contributed to 45.02% of the overall dissimilarity. Redundancy analysis (RDA) showed that the bacterioplankton community variation significantly correlated with chemical oxygen demand, phosphate, ammonium, and total organic carbon. Partial redundancy analysis (pRDA) was conducted in order to quantify the effect of the geographic distance between the two investigated areas on the differences between the bacteria communities. The results showed that the above-mentioned environmental factors in total contributed 38.18% of the bacteria community variation, while the geographic distance contributed only 10.66%, indicating that the influence of environmental factors on bacterial communities was much greater than that of the geographic distance. Overall, this study demonstrated that coastal aquaculture could cause eutrophication of rearing water, which, in turn, drove the variation of the bacterioplankton community, and remarkably altered the relative abundances of Bacteroidetes, Actinobacteria, and Gammaproteobacteria. The sensitivity of these bacteria to the concentration changes of pollutants, represented by nitrogen and phosphorus, indicates their potential usage in assessing the quality of aquaculture water and the health and stability of an aquaculture ecosystem.