Destabilisation of the holobiont macroalga and induction of bacterial pathogenesis due to increasing environmental stress conditions

海洋巨藻（海藻）的表面被复杂的细菌群落定植。最近已经证明，这些表细菌群落的组成是特定于宿主藻类的。这种关联中的干扰或变化可能危及整个实体的健康。在过去十年中，海带Ecklonia radiata的死亡率很高。致病性感染以及环境压力条件的增加，如气候变化导致的海水温度升高，可能是造成澳大利亚以及地球温带地区海带物种主要栖息地大量丧失的原因。迫切需要了解海藻全息体及其如何受到全球变暖趋势的影响，深入了解细菌全息体成员和促成这种特定宿主-微生物关联的因素。本研究旨在从澳大利亚南部开始，沿着水温梯度逐渐升高，直至该藻类的北部分布极限，在季节和区域尺度上研究辐射藻的组成和稳定性。结合温度控制的中生态实验，本研究将确定影响藻类全息生物稳定性的因素，并阐明该系统如何在环境压力条件下不稳定。本提案的总体目标是验证升高的环境应激条件直接影响藻类代谢物表面分泌的假设，这将破坏宿主藻类与其相关细菌之间的自然平衡。这反过来将为病原体提供导致感染的空间或将在自然关联中诱导发病机制。

Surfaces of marine macroalgae (seaweeds) are colonised by complex bacterial communities. It has recently been demonstrated that the composition of these epibacterial communities are specific to the host alga. Disturbances or shifts in this association can compromise the health of the whole entity. The kelp seaweed Ecklonia radiata has undergone high rates of mortality in the last decade. Pathogenic infections as well as increased environmental stress conditions, such as elevated seawater temperature due to climate change, are possibly causative for the tremendous loss of the dominant habitat forming kelp species in Australia, and more generally in temperate regions of the planet. Understanding the seaweed holobiont and how it is affected by global warming trends, in-depth knowledge of the bacterial holobiont members and the factors contributing to this specific host-microbe association is urgently required. This proposal aims to investigate the composition and stability of the holobiont E. radiata on a seasonal and regional scale along an increasing water temperature gradient beginning in the south of Australia towards the northern distributional limit of this alga. In combination with a temperature manipulated mesocosm experiment, this investigation will identify the factors contributing to the stability of the algal holobiont and elucidate how this system can be destabilized by environmental stress conditions. The overall goal of this proposal is to verify the hypothesis that elevated environmental stress conditions directly affect the surface exudation of algal metabolites which will destabilise the natural balance between host alga and its associated bacteria. This in turn will provide space for pathogens resulting in infection or will induce pathogenesis in natural associates.