Bourne David, Iida Yuki, Uthicke Sven, Smith-Keune Carolyn
Australian Institute of Marine Science, Townsville, Queensland, Australia.
ISME J. 2008 Apr;2(4):350-63. doi: 10.1038/ismej.2007.112. Epub 2007 Dec 6.
Environmental stressors such as increased sea surface temperatures are well-known for contributing to coral bleaching; however, the effect of increased temperatures and subsequent bleaching on coral-associated microbial communities is poorly understood. Colonies of the hard coral Acropora millepora were tagged on a reef flat off Magnetic Island (Great Barrier Reef) and surveyed over 2.5 years, which included a severe bleaching event in January/February 2002. Daily average water temperatures exceeded the previous 10-year average by more than 1 degrees C for extended periods with field-based visual surveys recording all tagged colonies displaying signs of bleaching. During the bleaching period, direct counts of coral zooxanthellae densities decreased by approximately 64%, before recovery to pre-bleaching levels after the thermal stress event. A subset of three tagged coral colonies were sampled through the bleaching event and changes in the microbial community elucidated. Denaturing gradient gel electrophoresis (DGGE) analysis demonstrated conserved bacterial banding profiles between the three coral colonies, confirming previous studies highlighting specific microbial associations. As coral colonies bleached, the microbial community shifted and redundancy analysis (RDA) of DGGE banding patterns revealed a correlation of increasing temperature with the appearance of Vibrio-affiliated sequences. Interestingly, this shift to a Vibrio-dominated community commenced prior to visual signs of bleaching. Clone libraries hybridized with Vibrio-specific oligonucleotide probes confirmed an increase in the fraction of Vibrio-affiliated clones during the bleaching period. Post bleaching, the coral microbial associations again shifted, returning to a profile similar to the fingerprints prior to bleaching. This provided further evidence for corals selecting and shaping their microbial partners. For non-bleached samples, a close association with Spongiobacter-related sequences were revealed by both clone libraries and DGGE profiling. Despite Vibrio species being previously implicated in bleaching of specific coral species, it is unsure if the relative increase in retrieved Vibrio sequences is due to bacterial infection or an opportunistic response to compromised health and changing environmental parameters of the coral host. This study provides the first molecular-based study demonstrating changes in coral-associated bacterial assemblages during a bleaching event on a natural reef system.
诸如海面温度升高之类的环境压力因素是导致珊瑚白化的众所周知的原因；然而，温度升高及随后的白化对与珊瑚相关的微生物群落的影响却鲜为人知。在磁岛（大堡礁）外的珊瑚礁坪上对硬珊瑚多孔鹿角珊瑚的群体进行了标记，并在2.5年的时间里进行了调查，其中包括2002年1月/2月的一次严重白化事件。日平均水温连续较长时间超过前10年平均水平1摄氏度以上，实地目视调查记录到所有标记的群体都显示出白化迹象。在白化期间，珊瑚共生藻密度的直接计数下降了约64%，在热应激事件后恢复到白化前的水平。在白化事件期间对三个标记的珊瑚群体进行了抽样，并阐明了微生物群落的变化。变性梯度凝胶电泳（DGGE）分析表明，这三个珊瑚群体之间的细菌条带图谱具有保守性，证实了之前强调特定微生物关联的研究。随着珊瑚群体白化，微生物群落发生了变化，对DGGE条带图谱的冗余分析（RDA）显示温度升高与弧菌属相关序列的出现存在相关性。有趣的是，这种向以弧菌为主的群落的转变在白化的目视迹象出现之前就开始了。与弧菌特异性寡核苷酸探针杂交的克隆文库证实，在白化期间弧菌属相关克隆的比例有所增加。白化后，珊瑚的微生物关联再次发生变化，恢复到与白化前指纹相似的图谱。这为珊瑚选择和塑造其微生物伙伴提供了进一步的证据。对于未白化的样本，克隆文库和DGGE分析都显示与海绵杆菌相关序列有密切关联。尽管弧菌属物种之前被认为与特定珊瑚物种的白化有关，但尚不确定检索到的弧菌序列相对增加是由于细菌感染还是对珊瑚宿主健康受损和环境参数变化的机会性反应。这项研究提供了第一项基于分子的研究，证明了在天然珊瑚礁系统的白化事件中与珊瑚相关的细菌组合的变化。
