The symbiont “Candidatus Aquarickettsia rohweri” infects a diversity of aquatic hosts. In the threatened Caribbean coral, Acropora cervicornis, Aquarickettsia proliferates in response to increased nutrient exposure, resulting in suppressed growth and increased disease susceptibility and mortality of coral. This study evaluated the extent, as well as the ecology and evolution of Aquarickettsia infecting threatened corals, Ac. cervicornis, and Ac. palmata and their hybrid (“Ac. prolifera”). Aquarickettsia was found in all acroporids, with coral host and geographic location impacting the infection magnitude. Phylogenomic and genome-wide single-nucleotide variant analysis of Aquarickettsia found phylogenetic clustering by geographic region, not by coral taxon. Analysis of Aquarickettsia fixation indices suggests multiple sequential infections of the same coral colony are unlikely. Furthermore, relative to other Rickettsiales species, Aquarickettsia is undergoing positive selection, with Florida populations experiencing greater positive selection relative to other Caribbean locations. This may be due in part to Aquarickettsia proliferating in response to greater nutrient stress in Florida, as indicated by greater in situ replication rates in these corals. Aquarickettsia was not found to significantly codiversify with either the coral animal or the coral’s algal symbiont (Symbiodinium “fitti”). Quantitative PCR analysis showed that gametes, larvae, recruits, and juveniles from susceptible, captive-reared coral genets were not infected with Aquarickettsia. Thus, horizontal transmission of Aquarickettsia via coral mucocytes or an unidentified host is more likely. The prevalence of Aquarickettsia in Ac. cervicornis and its high abundance in the Florida coral population suggests that coral disease mitigation efforts focus on preventing early infection via horizontal transmission.

共生体“ Candidatus Aquarickettsia rohweri”感染多种水生宿主。在受到威胁的加勒比珊瑚中，鹿角鹿角珊瑚（Aquarickettsia）因营养暴露增加而增殖，导致珊瑚生长受到抑制，疾病易感性和死亡率增加。这项研究评估了Aquarickettsia感染受威胁珊瑚Ac的程度以及生态和进化。颈角和Ac。palmata及其杂交种（“ Ac. prolifera ”）。水立克次体存在于所有顶孔类动物中，珊瑚宿主和地理位置影响感染程度。对Aquarickettsia的系统发育和全基因组单核苷酸变异分析发现，系统发育按地理区域而不是按珊瑚分类群进行聚类。对Aquarickettsia固定指数的分析表明，同一珊瑚群不太可能发生多次连续感染。此外，相对于其他立克次体物种，水立克次体正在经历正选择，佛罗里达种群相对于其他加勒比地区经历了更大的正选择。这可能部分是由于水立克次体在佛罗里达州因应对更大的营养压力而增殖，这些珊瑚的原位复制率更高就表明了这一点。没有发现Aquarickettsia与珊瑚动物或珊瑚的藻类共生体（ Symbiodinium “ fitti ”）显着共同多样化。定量 PCR 分析表明，来自易受影响的圈养珊瑚基因组的配子、幼虫、新成员和幼体没有感染Aquarickettsia。因此，Aquarickettsia通过珊瑚粘细胞或不明宿主进行水平传播的可能性更大。Ac中Aquarickettsia的流行。cervicornis及其在佛罗里达珊瑚种群中的大量存在表明，缓解珊瑚疾病的努力重点是防止通过水平传播进行早期感染。