Cano Irene, Ryder David, Webb Steve C, Jones Brian J, Brosnahan Cara L, Carrasco Noelia, Bodinier Barbara, Furones Dolors, Pretto Tobia, Carella Francesca, Chollet Bruno, Arzul Isabelle, Cheslett Deborah, Collins Evelyn, Lohrmann Karin B, Valdivia Ana L, Ward Georgia, Carballal María J, Villalba Antonio, Marigómez Ionan, Mortensen Stein, Christison Kevin, Kevin Wakeman C, Bustos Eduardo, Christie Lyndsay, Green Matthew, Feist Stephen W
International Centre of Excellence for Aquatic Animal Health, Cefas Weymouth Laboratory, Weymouth, United Kingdom.
Cawthron Institute, Nelson, New Zealand.
Front Microbiol. 2020 Oct 30;11:577481. doi: 10.3389/fmicb.2020.577481. eCollection 2020.
Intracellular microcolonies of bacteria (IMC), in some cases developing large extracellular cysts (bacterial aggregates), infecting primarily gill and digestive gland, have been historically reported in a wide diversity of economically important mollusk species worldwide, sometimes associated with severe lesions and mass mortality events. As an effort to characterize those organisms, traditionally named as -like organisms, 1950 specimens comprising 22 mollusk species were collected over 10 countries and after histology examination, a selection of 99 samples involving 20 species were subjected to 16S rRNA gene amplicon sequencing. Phylogenetic analysis showed sequences in all the mollusk species analyzed. Geographical differences in the distribution of Operational Taxonomic Units (OTUs) and a particular OTU associated with pathology in king scallop (OTU_2) were observed. The presence of sequences in the IMC was visually confirmed by hybridization (ISH) in eight selected samples. Sequencing data also indicated other symbiotic bacteria. Subsequent phylogenetic analysis of those OTUs revealed a novel microbial diversity associated with molluskan IMC infection distributed among different taxa, including the phylum Spirochetes, the families and , the genera and , and sulfur-oxidizing endosymbionts. Sequences like and Brownia rhizoecola were also obtained, however, in the absence of ISH studies, the association between those organisms and the IMCs were not confirmed. The sequences identified in this study will allow for further molecular characterization of the microbial community associated with IMC infection in marine mollusks and their correlation with severity of the lesions to clarify their role as endosymbionts, commensals or true pathogens.
细菌的细胞内微菌落（IMC），在某些情况下会形成大型细胞外囊肿（细菌聚集体），主要感染鳃和消化腺，历史上在全球多种具有经济重要性的软体动物物种中都有报道，有时与严重病变和大规模死亡事件有关。为了对这些传统上被称为“类生物体”的生物进行特征描述，在10个国家收集了包含22种软体动物的1950个标本，经过组织学检查后，从涉及20个物种的99个样本中选取进行16S rRNA基因扩增子测序。系统发育分析显示了所有分析的软体动物物种中的序列。观察到操作分类单元（OTU）分布的地理差异以及与王扇贝病理学相关的一个特定OTU（OTU_2）。通过对八个选定样本进行原位杂交（ISH）在视觉上证实了IMC中序列的存在。测序数据还表明存在其他共生细菌。随后对这些OTU的系统发育分析揭示了与软体动物IMC感染相关的新的微生物多样性，分布在不同的分类群中，包括螺旋体门、和科、和属以及硫氧化内共生体。还获得了和根际布朗氏菌等序列，然而，由于缺乏ISH研究，这些生物体与IMC之间的关联尚未得到证实。本研究中鉴定的序列将有助于对与海洋软体动物IMC感染相关的微生物群落进行进一步的分子特征描述，以及它们与病变严重程度的相关性，以阐明它们作为内共生体、共栖生物或真正病原体的作用。
