Identification of bacterial populations associated with the Pacific oyster, Crassostrea gigas from larvae to seed in hatchery

The microbiota of larvae and postlarvae of oyster reared in recycling system was monitored during 44 day. As soon as day 2, it appeared diversified and specific, as compared to the bacterial assemblages in seawater. Major shifts occurred during larval development, notably during metamorphosis, likely due to the modifications of oyster anatomy and physiology. On day 44 the seed microbiota diverged with only 44.2% of similarity in average between the different batches. In oyster seed, the core microbiota was composed of Burkholderiales (20 OTUs), Xanthomonales (13 OTUs), a-Proteobacteria (13 OTUs) and candidate phylum TM6 (1 OTU). A noticeable part of the microbiota in seed comprised OTUs already present on day 2 and several dominant taxa were identified two years earlier. This revealed a certain containment of bacterial populations in hatchery that could lead their impoverishment. Nonetheless its diversity remained high, even when bacterial populations of seawater were dominated by two OTUs belonging to Bacteriovoracaceae and Cryomorphaceae. Furthermore none bacterial opportunist or pathogen was detected. Finally since the microbiota, established in hatchery reared seed appeared diverse and may deeply change, it should not weaken them in front of the diseases which have recently emerged.

本研究对循环养殖系统中培育的牡蛎幼体及仔稚体的微生物群（microbiota）开展了为期44天的动态监测。早在第2天，该微生物群即已呈现出与海水细菌群落（bacterial assemblages）显著不同的多样性与特异性。幼体发育过程中（尤其是变态阶段），微生物群发生了显著的群落更替，这大概率与牡蛎的解剖结构及生理机能的改变相关。至第44天时，不同批次的牡蛎苗种微生物群已出现明显分化，组间平均相似性仅为44.2%。在牡蛎苗种的核心微生物群中，伯克霍尔德氏菌目（Burkholderiales，20个操作分类单元（Operational Taxonomic Unit，OTU））、黄单胞菌目（Xanthomonales，13个OTU）、α-变形菌纲（α-Proteobacteria，13个OTU）以及候选门TM6（candidate phylum TM6，1个OTU）为主要组成类群。苗种微生物群中有相当一部分OTU可追溯至第2天即已存在的类群，且部分优势类群早在两年前即可被检测到。这反映出育苗场环境中细菌种群存在一定的封闭性，可能导致菌群多样性逐步降低。尽管如此，苗种微生物群的多样性仍维持在较高水平，即便此时海水细菌种群仅由隶属于噬菌弧菌科（Bacteriovoracaceae）和冷绳菌科（Cryomorphaceae）的两个OTU所主导。此外，本研究未检测到任何细菌机会致病菌或病原菌。最后，由于育苗场培育的牡蛎苗种其微生物群结构多样且可能发生显著改变，因此在近期新发水产病害面前，苗种的抗病能力并不会因此受到削弱。