Due to climate changes and eutrophication, blooms of predominantly toxic freshwater cyanobacteria are intensifying and are likely to colonize estuaries, thus impacting benthic organisms and shellfish farming representing a major ecological, health and economic risk. In the natural environment, form large mucilaginous colonies that influence the development of both cyanobacterial and embedded bacterial communities. However, little is known about the fate of natural colonies of by salinity increase. In this study, we monitored the fate of a dominated bloom and its microbiome along a French freshwater-marine gradient at different phases of a bloom. We demonstrated changes in the cyanobacterial genotypic composition, in the production of specific metabolites (toxins and compatible solutes) and in the heterotrophic bacteria structure in response to the salinity increase. In particular and survived salinities up to 20. Based on microcystin gene abundance, the cyanobacteria became more toxic during their estuarine transfer but with no selection of specific microcystin variants. An increase in compatible solutes occurred along the continuum with extensive trehalose and betaine accumulations. Salinity structured most the heterotrophic bacteria community, with an increased in the richness and diversity along the continuum. A core microbiome in the mucilage-associated attached fraction was highly abundant suggesting a strong interaction between and its microbiome and a likely protecting role of the mucilage against an osmotic shock. These results underline the need to better determine the interactions between the colonies and their microbiome as a likely key to their widespread success and adaptation to various environmental conditions.

中文翻译：

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有毒蓝藻群落及其相关微生物组沿着淡水-海洋连续体的时空连接

由于气候变化和富营养化，主要有毒的淡水蓝藻的繁殖正在加剧，并可能在河口繁殖，从而影响底栖生物和贝类养殖，构成重大生态、健康和经济风险。在自然环境中，形成大型粘液菌落，影响蓝藻和嵌入细菌群落的发展。然而，人们对盐度增加导致的自然菌落的命运知之甚少。在这项研究中，我们沿着法国淡水-海洋梯度在水华的不同阶段监测了主导水华及其微生物组的命运。我们证明了蓝藻基因型组成、特定代谢物（毒素和相容性溶质）的产生以及异养细菌结构因盐度增加而发生的变化。特别是在盐度高达 20 的情况下仍能存活。根据微囊藻毒素基因丰度，蓝藻在河口转移过程中毒性更强，但没有选择特定的微囊藻毒素变体。随着海藻糖和甜菜碱的大量积累，相容性溶质沿着连续体发生增加。盐度构成了异养细菌群落的大部分，随着连续体的丰富度和多样性的增加。粘液相关附着部分中的核心微生物组非常丰富，表明其微生物组之间存在很强的相互作用，并且粘液可能具有针对渗透压休克的保护作用。这些结果强调需要更好地确定菌落与其微生物组之间的相互作用，这可能是它们广泛成功和适应各种环境条件的关键。