Bacterial genetic diversity on settlement substrates during mass mortality of larvae of nona-porous abalone (Haliotis diversicolor supertexta)

Settlement substrate samples for nona-porous abalone seed attachment from diseased and nondiseased abalone hatcheries during mass mortality occurrence were collected, the 16S rRNA gene clone libraries of the attachments were constructed using primers universal for the domain Bacteria. In total, 83 clones randomly selected were screened by PCR-restriction fragment length polymorphism (PCR-RFLP) analysis and clones with unique RFLP patterns were sequenced. Phylogenetic analysis revealed bacterial components different from previous studies in such environments. Apart from sequences originating from chloroplast of eukaryotic diatom (occupying 29.33%), all the cloned sequences fell into five lineages of the bacterial domains, the α-Proteobacteria, γ-Proteobacteria, Flavobacteria, Acidobacteria and an uncultured candidate division TM7. The α-Proteobacteria was predominant (56%) and was mainly comprised of Sphingomonadales, Rhodobacterales, and Rhizobiales affiliated clones. Other groups appeared just as minor components. Most of our sequences were closely related to sequences from attached bacteria, or sequences retrieved from extreme environments or specific environments, indicating that these bacteria might play an important function in bacterial attachment or in extreme environments. The community structure and the clone abundance in different groups of the two clone libraries were different, further research focusing on these different bacteria will help to reveal the potential pathogens of the abalones' mass mortality.