Bacterial composition of sponges, sediment and seawater in enclosed and open marine lakes in Ha Long Bay Vietnam

Marine lakes are landlocked bodies of seawater, isolated to varying degrees from the surrounding marine habitat. Isolated lakes generally have lower pH values, salinities and higher temperatures than more open lakes. We used a 16S rRNA gene barcoded pyrosequencing approach to study the bacterial communities of two sponge species, sediment and seawater in one enclosed and two open marine lakes. Bacterial communities of the sponge Spheciospongia solida mainly consisted of Proteobacteria, Cyanobacteria and Bacteroidetes. In contrast, Proteobacteria, Chloroflexi and Acidobacteria dominated the bacterial communities of the sponge Spongia ceylonensis. Although only a limited amount of samples were collected, both water and S. ceylonensis sponge had higher relative abundances of Cyanobacteria in the enclosed lake, which mainly consisted of OTUs assigned to the genus Synechococcus. This is in line with a number of previous studies, which have shown that environmental conditions found within low pH environments such as marine lakes benefit the growth of Synechococcus spp. Future studies should address the mechanism by which Synechococcus spp. may help host sponges and their bacterial communities adapt to low pH conditions in isolated marine lakes and other low-pH environments.

海洋湖泊是被陆地环绕的海水水体，与周边海洋生境存在不同程度的隔离。相较于开放型海洋湖泊，封闭型海洋湖泊的pH值、盐度通常更低，而温度更高。本研究采用16S核糖体RNA基因条形码焦磷酸测序法，对1个封闭型及2个开放型海洋湖泊中的2种海绵、沉积物及海水的细菌群落展开了研究。

海绵物种Spheciospongia solida的细菌群落主要由变形菌门（Proteobacteria）、蓝细菌门（Cyanobacteria）和拟杆菌门（Bacteroidetes）构成。与之相对，锡兰海绵（Spongia ceylonensis）的细菌群落则以变形菌门、绿弯菌门（Chloroflexi）和酸杆菌门（Acidobacteria）为优势类群。

尽管本次研究采集的样本量有限，但封闭型湖泊中的水体及锡兰海绵的蓝细菌相对丰度均更高，这些蓝细菌主要归类为聚球藻属（Synechococcus）的操作分类单元（Operational Taxonomic Units，OTUs）。

该结果与此前多项研究结论相符，即海洋湖泊等低pH环境中的环境条件有利于聚球藻属（Synechococcus spp.）的生长。

未来的研究应进一步阐明聚球藻属物种如何帮助宿主海绵及其细菌群落适应封闭型海洋湖泊及其他低pH环境中的低pH条件。