St. Petersburg Coastal and Marine Science Center, U.S. Geological Survey, St. Petersburg, Florida, United States of America.
Smithsonian Marine Station, Ft. Pierce, Florida, United States of America.
PeerJ. 2023 Aug 23;11:e15836. doi: 10.7717/peerj.15836. eCollection 2023.
Effective treatment and prevention of any disease necessitates knowledge of the causative agent, yet the causative agents of most coral diseases remain unknown, in part due to the difficulty of distinguishing the pathogenic microbe(s) among the complex microbial backdrop of coral hosts. Stony coral tissue loss disease (SCTLD) is a particularly destructive disease of unknown etiology, capable of transmitting through the water column and killing entire colonies within a matter of weeks. Here we used a previously described method to (i) isolate diseased and apparently healthy coral colonies within individual mesocosms containing filtered seawater with low microbial background levels; (ii) incubate for several days to enrich the water with coral-shed microbes; (iii) use tangential-flow filtration to concentrate the microbial community in the mesocosm water; and then (iv) filter the resulting concentrate through a sequential series of different pore-sized filters. To investigate the size class of microorganism(s) associated with SCTLD transmission, we used 0.8 µm pore size filters to capture microeukaryotes and expelled zooxanthellae, 0.22 µm pore size filters to capture bacteria and large viruses, and 0.025 µm pore size filters to capture smaller viruses. In an attempt to further refine which size fraction(s) contained the transmissible element of SCTLD, we then applied these filters to healthy "receiver" coral fragments and monitored them for the onset of SCTLD signs over three separate experimental runs. However, several factors outside of our control confounded the transmission results, rendering them inconclusive. As the bulk of prior studies of SCTLD in coral tissues have primarily investigated the associated bacterial community, we chose to characterize the prokaryotic community associated with all mesocosm 0.22 µm pore size filters using Illumina sequencing of the V4 region of the 16S rRNA gene. We identified overlaps with prior SCTLD studies, including the presence of numerous previously identified SCTLD bioindicators within our mesocosms. The identification in our mesocosms of specific bacterial amplicon sequence variants that also appear across prior studies spanning different collection years, geographic regions, source material, and coral species, suggests that bacteria may play some role in the disease.
有效治疗和预防任何疾病都需要了解病原体，但大多数珊瑚疾病的病原体仍不清楚，部分原因是难以区分珊瑚宿主复杂微生物背景中的致病微生物。石珊瑚组织损失疾病（SCTLD）是一种特别具有破坏性的病因不明的疾病，能够通过水柱传播，并在数周内杀死整个珊瑚礁。在这里，我们使用了先前描述的方法来：(i) 在含有低微生物背景水平过滤海水的单个中观室内分离出患病和明显健康的珊瑚礁；(ii) 孵育数天，使珊瑚脱落的微生物在水中富集；(iii) 使用切向流过滤浓缩中观室内的微生物群落；然后 (iv) 通过一系列不同孔径的过滤器过滤浓缩物。为了研究与 SCTLD 传播相关的微生物（大小类群），我们使用 0.8 µm 孔径的过滤器捕获微真核生物和排出的虫黄藻，使用 0.22 µm 孔径的过滤器捕获细菌和大型病毒，使用 0.025 µm 孔径的过滤器捕获较小的病毒。为了进一步研究与 SCTLD 传播相关的大小类群，我们将这些过滤器应用于健康的“受体”珊瑚碎片，并在三个独立的实验运行中监测它们出现 SCTLD 症状的情况。然而，由于一些超出我们控制的因素干扰了传播结果，使其无法得出结论。由于之前对珊瑚组织中 SCTLD 的大部分研究主要调查了相关的细菌群落，因此我们选择使用 Illumina 对 16S rRNA 基因 V4 区进行测序，对所有中观室 0.22 µm 孔径过滤器上相关的原核生物群落进行特征描述。我们发现与之前的 SCTLD 研究存在重叠，包括在我们的中观室内存在许多之前确定的 SCTLD 生物标志物。在我们的中观室内鉴定出的特定细菌扩增子序列变体也出现在之前跨越不同收集年份、地理区域、来源材料和珊瑚物种的研究中，这表明细菌可能在疾病中发挥了一定作用。
