Stress Induced Coral Mortality: The Role of Opportunistic Bacterial Infections

在过去的三十年里，珊瑚礁的数量急剧减少。可能有几个因素促成了这一过程，包括过度捕捞、二氧化碳水平上升、海洋表面温度变化、富营养化、沉积物和污染物。然而，这些应激源中的大多数与珊瑚礁衰退之间的因果关系尚未确定。在过去的二十年里，珊瑚疾病的发病率也出现了惊人的增长。这些疾病中的大多数原因尚不清楚，但这些疾病继续导致珊瑚大量死亡。在已报道的29种珊瑚疾病中，只有两种病原体被分离出来，符合科赫的假设。一些未确诊的疾病是由机会性的病原体引起的，而不是特定的病原体吗？珊瑚疾病的发病率和人类活动是相关的。同样，这两个观察结果之间的因果联系，如果有的话，也是未知的。罗威尔博士及其同事提出，暴露在人为和环境压力下的珊瑚容易受到机会性感染，从而导致珊瑚死亡和疾病。在初步研究中，他们发现通常生活在珊瑚上的微生物群落由特定的细菌组成，这些细菌以受控的速度生长。例如，生活在相距遥远的百慕大和巴拿马珊瑚礁上的珊瑚具有独特的微生物群，这种微生物群是个别珊瑚物种特有的。他们还观察到，健康珊瑚之间的细菌数量和生长速度非常相似。当珊瑚暴露在紧张的环境或人为条件下时，珊瑚与其相关微生物群落之间的关系迅速发生变化。在实验中，添加有机营养物质会迅速导致珊瑚死亡，这是通过添加抗生素来防止的。这有力地表明细菌的过度生长是应激源诱导的死亡的原因。其他研究人员已经证明，包括沉积物、原油和硫酸铜在内的压力因素导致的珊瑚死亡可以通过使用抗生素来预防。研究人员还证明，与健康的珊瑚相比，患病珊瑚上的细菌数量和产量都增加了一个数量级以上。在这项研究中，他们将表征正常范围的微生物生长参数和原核生物多样性在健康的，非应激状态下的法兰克氏分支杆菌。然后，他们将用一些潜在的应激源来处理珊瑚，以确定哪些珊瑚会通过导致微生物过度生长而死亡。最后，他们将监测细菌生长和群落组成的变化，这些变化发生在机会性细菌感染时。这项研究将提高我们对珊瑚与其相关细菌群落之间的关系，以及这种关系如何随着压力和疾病的变化的理解。这项研究还将更好地了解人类活动与珊瑚疾病发病率之间的联系，为珊瑚礁的养护和管理提供重要数据。

Coral reefs have declined dramatically over the last three decades. Several factors may have contributed to this process, including over-fishing, increasing CO2 levels, changes in sea surface temperatures, eutrophication, sedimentation, and pollutants. However the causal relationship between most of these stressors and reef decline has yet to be established. There has also been an alarming increase in coral disease incidence during the last two decades. The causes of the majority of these diseases remain unknown yet the diseases continue to cause massive die offs of corals. Of the 29 coral diseases that have been reported, only two pathogens have been isolated which fulfill Koch's postulates. Are some of the undiagnosed diseases caused by opportunistic, rather than specific, pathogens? Coral disease incidences and human activity are correlated. Again, the causal connection, if any, between these two observations is not known. Dr. Rohwer and associates suggest that corals exposed to anthropogenic and environmental stressors become susceptible to opportunistic infection resulting in coral mortality and disease. In preliminary studies, they have found that the microbial community normally living on corals consists of specific bacteria growing at a controlled rate. For example, corals living on reefs as far apart as Bermuda and Panama have characteristic microbiotas, that are specific to individual coral species. They have also observed that bacterial numbers and growth rates are very similar between healthy corals. The relationship between the coral and its associated microbial community rapidly changes when the coral is exposed to stressful environmental or anthropogenic conditions. In experiments, additions of organic nutrients rapidly lead to coral death, which was prevented by adding antibiotics. This strongly suggests that bacterial overgrowth is responsible for the stressor-induced mortality. Other investigators have shown that coral mortality caused by stressors, including sedimentation, crude oil, and copper sulfate, could be prevented using antibiotics. The investigators have also documented that both bacterial numbers and production rates increase by over an order of magnitude on diseased, as compared to healthy, corals. In this research, they will characterize the normal range of microbial growth parameters and prokaryotic diversity on healthy, unstressed M. franksi. They will then treat corals with a number of potential stressors to determine which kill corals by causing microbial overgrowth. Finally, they will monitor changes in bacterial growth and community composition that occurs with opportunistic bacterial infection. This research will improve our understanding of the relationship between a coral and its associated bacterial community, and how this relationship changes with stress and disease. This research will also provide a better understanding of the connection between human activities and the incidence of coral disease, providing important data for the conservation and management of coral reefs.