The Sydney rock oyster (SRO; Saccostrea glomerata) is the most intensively farmed oyster species in Australia however, Queensland unknown (QX) disease has resulted in substantial losses and impeded productivity. QX disease is caused by infection with the parasite Marteilia sydneyi, and like other diseases, outbreaks are driven by a series of complex environmental and host factors such as seasonality, seawater salinity and oyster genetics. A potential but understudied factor in QX disease is the SRO microbiota, which we sought to examine before and during a QX disease outbreak. Using 16S rRNA (V1 – V3 region) amplicon sequencing, we examined the microbiota of SROs deployed in an estuary where QX disease occurs, with sampling conducted fortnightly over 22 weeks. Marteilia sydneyi was detected in the SROs by PCR (QX-positive), 16 weeks after the first sampling event and sporonts were observed in the digestive gland two weeks later on. There were no apparent patterns observed between the microbiota of QX-positive SROs with and without digestive gland sporonts however, the microbiota of QX-positive SROs was significantly different from those sampled prior to detection of M. sydneyi and from those negative for M. sydneyi post detection. As a result, shifts in microbiota structure occurred before sporulation in the digestive gland and either before or shortly after pathogen colonisation. The microbiota shifts associated with QX-positive oysters were principally driven by a relative abundance increase of operational taxonomic units (OTUs) assigned to unclassified species of the Borrelia and Candidatus Hepatoplasma genera and a relative abundance decrease in an OTU assigned to an unclassified species of the Mycoplasma genus. Since Mycoplasma species are common microbiota features of SROs and other oysters, we propose that there may be an important ecological link between Mycoplasma species and the health state of SROs.

悉尼牡蛎（SRO; Saccostrea glomerata）是澳大利亚养殖最密集的牡蛎种类，然而，昆士兰未知（QX）病已导致大量损失和生产力下降。QX疾病是由寄生虫Martyilia sydneyi感染引起的，与其他疾病一样，暴发是由一系列复杂的环境和宿主因素驱动的，例如季节性，海水盐度和牡蛎遗传学。SRO微生物群是QX疾病中一个潜在但未被充分研究的因素，我们试图在QX疾病爆发之前和之中进行检查。使用16S rRNA（V1-V3区域）扩增子测序，我们检查了在QX病发生的河口部署的SRO微生物群，每22周取样两次。第一个采样事件发生后16周，通过PCR（QX阳性）在SRO中检测到了马氏ilia，两周后在消化腺中观察到孢子体。在有和没有消化腺孢子体的QX阳性SRO的菌群之间没有观察到明显的模式，但是，QX阳性SRO的菌群与检测悉尼分枝杆菌之前的样本和悉尼分枝杆菌阴性的样本都存在显着差异。事后检测。结果，微生物群结构发生了变化，发生在消化腺中的孢子形成之前以及病原体定殖之前或之后不久。与QX阳性牡蛎有关的微生物群变化主要是由分配给未分类的疏螺旋体和假丝酵母肝菌属的操作分类单位（OTU）相对丰度增加和分配给未分类的牡蛎属的OTU相对丰度降低所驱动的。支原体属。由于支原体物种是SRO和其他牡蛎的常见微生物群特征，因此我们建议支原体物种与SRO的健康状态之间可能存在重要的生态联系。