Ren Minglei, Zhang Guiying, Ye Zi, Qiao Zhixian, Xie Meili, Lin Yan, Li Tao, Zhao Jindong
State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China.
Simon F. S. Li Marine Science Laboratory, School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China.
AMB Express. 2017 Nov 2;7(1):193. doi: 10.1186/s13568-017-0490-2.
Disentangling the interactions between cyanobacteria and associated bacterial community is important for understanding the mechanisms that mediate the formation of cyanobacterial blooms in freshwater ecosystems. Despite the fact that a metagenomic approach enables researchers to profile the structure of microbial communities associated with cyanobacteria, reconstructing genome sequences for all members remains inefficient, due to the inherent enormous microbial diversity. Here, we have established a stable coculture system under high salinity, originally from a mixture of an axenic cyanobacterium Synechococcus sp. PCC 7002 and a non-axenic bloom-forming cyanobacterium Microcystis colony. Metagenomic analysis showed that the coculture consists of S. sp. PCC 7002 and two heterotrophic bacteria, designated as Pseudomonas stutzeri TAIHU and Mesorhizobium sp. TAIHU, respectively. And near-complete genome sequences of both bacteria were reconstructed from the metagenomic dataset with an average completeness of 99.8%. Genome-wide pathway analysis revealed that M. sp. TAIHU carried all the genes involved in the de novo biosynthesis of cobalamin, which is required by S. sp. PCC 7002 for growth. To cope with the high salinity in the coculture, experimental evidence demonstrated that S. sp. PCC 7002 would synthesize the compatible solutes including sucrose and glucosylglycerol, which are supposed to be exploited by both heterotrophic bacteria as potential carbon and/or nitrogen sources. Furthermore, the genes encoding for the biosynthesis of the ectoine, another common osmolyte are found exclusively in P. stutzeri TAIHU, while the genes responsible for the catabolism of ectoine and its derives are present only in M. sp. TAIHU. These genomic evidence indicates beneficial interaction between three members in the coculture. Establishment of the coculture system with relative simplicity provides a useful model system for investigating the interspecies interactions, and genome sequences of both bacteria associated with Microcystis bloom described here will facilitate the researcher to elucidate the role of these heterotrophic bacteria in the formation and maintenance of cyanobacterial bloom in freshwater ecosystem.
理清蓝藻与相关细菌群落之间的相互作用，对于理解淡水生态系统中蓝藻水华形成的介导机制至关重要。尽管宏基因组学方法使研究人员能够描绘与蓝藻相关的微生物群落结构，但由于固有的巨大微生物多样性，重建所有成员的基因组序列仍然效率低下。在此，我们在高盐度条件下建立了一个稳定的共培养系统，最初源自无菌蓝藻聚球藻属PCC 7002和非无菌的形成水华的蓝藻微囊藻菌落的混合物。宏基因组分析表明，该共培养物由聚球藻属PCC 7002和两种异养细菌组成，分别命名为施氏假单胞菌TAIHU和中生根瘤菌属TAIHU。从宏基因组数据集中重建了这两种细菌的近乎完整的基因组序列，平均完整性为99.8%。全基因组途径分析表明，中生根瘤菌属TAIHU携带了聚球藻属PCC 7002生长所需的钴胺素从头生物合成所涉及的所有基因。为了应对共培养中的高盐度，实验证据表明聚球藻属PCC 7002会合成包括蔗糖和葡糖基甘油在内的相容性溶质，这些溶质应该会被两种异养细菌作为潜在的碳和/或氮源利用。此外，编码另一种常见渗透溶质四氢嘧啶生物合成的基因仅在施氏假单胞菌TAIHU中发现，而负责四氢嘧啶及其衍生物分解代谢的基因仅存在于中生根瘤菌属TAIHU中。这些基因组证据表明共培养中三个成员之间存在有益的相互作用。相对简单的共培养系统的建立为研究种间相互作用提供了一个有用的模型系统，此处描述的与微囊藻水华相关的两种细菌的基因组序列将有助于研究人员阐明这些异养细菌在淡水生态系统中蓝藻水华形成和维持中的作用。
