Abstract:

The quantity and the bacterial communities in the digestive tract, gill, and foot of Haliotis discus hannai after infection with Vibrio harveyi were studied using Illumina sequencing technology. Results showed that nine phyla of bacteria were detected in the digestive tract, gills, and foot muscles of H.discus hannai, with Proteobacteria being the dominant phylum, accounting for 30.1%~64.4%, 37.45%~70.6%, and 71.1%~85.9% of the tissues. Bacteroidetes (5.53%~46.09%), Fusobacteria (4.43%~36.80%) and Tenericutes (0.60%~28.77%) were the sub-dominant phyla, while five other phyla including Actinobacteria and some unknown taxa were also detected. At the genus level, the dominant genera in the digestive tract of H.discus hannai were Mycoplasma (15.85%~34.55%) and in the gill was Pseudomonas (54.81%). The dominant genera in the foot muscles were Pseudomonas (44.83%~69.76%) and Curvibacter (21.24%). There were also genera such as Pelomonas. After the introduction of the pathogenic V. harveyi, the quantity of vibrios in the digestive tract increased from 7.2×10⁵cfu·mL^-1 to 10.9×10⁵cfu·mL^-1 as the stress time increased; the quantity of vibrio in the blood increased from 2×10³cfu·mL^-1 to 4.7×10³cfu·mL^-1; the quantity of vibrios in the foot muscle decreased after 48 h of V. harveyi stress and increased in the foot muscle at all other time. The Ace and Chao indices of the abalone digestive tract, gills, and foot muscles were lower than those of the control group at all time, except for the Ace and Chao indices of the abalone digestive tract after 24 h of V. harveyi stress and the Ace index of the digestive tract after 96 h of stress. The Shannon index was higher than the control in the digestive tract and foot at 24 h and in gill at 96h after V. harveyi infection and lower than the control at the remaining time. The introduction of V. harveyi increased the abundance of the Bacteroidetes as well as Fusobacteria in the digestive tract; the abundance of Proteobacteria in the gill decreased while that of Fusobacteria increased; the abundance of Proteobacteria in the foot muscles increased and that of Bacteroidetes decreased. At the genus level, the abundance of Pseudomonas, Bacteroides, and Propionibacterium increased and the abundance of Mycoplasma decreased in the digestive tract, except for a few time; the abundance of Bacteroides, Kordia, and Propionibacterium increased in gill; and the abundance of Pseudomonas increased in foot muscles. This study investigated the effect of the common pathogen V. harveyi on the quantity and the bacterial communities of the host flora from a microecological perspective and provided a new idea for further research on the response mechanism of the host to the pathogen V. harveyi and the prevention and control of vibriosis.

Keywords Vibrio harveyi; Haliotis discus hannai; bacterial diversity