Peerakietkhajorn Saranya, Tsukada Koji, Kato Yasuhiko, Matsuura Tomoaki, Watanabe Hajime
Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan.
Environ Microbiol Rep. 2015 Apr;7(2):364-72. doi: 10.1111/1758-2229.12260. Epub 2015 Feb 12.
The filter-feeding crustacean Daphnia is a key organism in freshwater ecosystems. Here, we report the effect of symbiotic bacteria on ecologically important life history traits, such as population dynamics and longevity, in Daphnia magna. By disinfection of the daphniid embryos with glutaraldehyde, aposymbiotic daphniids were prepared and cultured under bacteria-free conditions. Removal of bacteria from the daphniids was monitored by quantitative polymerase chain reaction for bacterial 16S rRNA gene. The population of aposymbiotic daphniids was reduced 10-folds compared with that of the control daphniids. Importantly, re-infection with symbiotic bacteria caused daphniids to regain bacteria and increase their fecundity to the level of the control daphniids, suggesting that symbiotic bacteria regulate Daphnia fecundity. To identify the species of symbiotic bacteria, 16S rRNA genes of bacteria in daphniids were sequenced. This revealed that 50% of sequences belonged to the Limnohabitans sp. of the Betaproteobacteria class and that the diversity of bacterial taxa was relatively low. These results suggested that symbiotic bacteria have a beneficial effect on D. magna, and that aposymbiotic Daphnia are useful tools in understanding the role of symbiotic bacteria in the environmental responses and evolution of their hosts.
滤食性甲壳动物水蚤是淡水生态系统中的关键生物。在此，我们报告共生细菌对大型溞生态上重要的生活史特征（如种群动态和寿命）的影响。通过用戊二醛对水蚤胚胎进行消毒，制备了无共生菌的水蚤，并在无菌条件下培养。通过对细菌16S rRNA基因进行定量聚合酶链反应监测水蚤体内细菌的去除情况。与对照水蚤相比，无共生菌水蚤的种群数量减少了10倍。重要的是，用共生细菌重新感染使水蚤重新获得细菌，并使其繁殖力提高到对照水蚤的水平，这表明共生细菌调节水蚤的繁殖力。为了鉴定共生细菌的种类，对水蚤体内细菌的16S rRNA基因进行了测序。结果显示，50%的序列属于β-变形菌纲的栖湖菌属，且细菌类群的多样性相对较低。这些结果表明共生细菌对大型溞有有益影响，并且无共生菌水蚤是理解共生细菌在其宿主的环境反应和进化中作用的有用工具。
