Characteristics and Correlation Analysis of Bacterial Community Structure in the Gut of Apostichopus japonicus and Culture Water in Suspension Cages from North China

Abstract

Owing to its high economic and nutritional value, Apostichopus japonicus is an important mariculture species in North China. Because of the rapid development of its aquaculture industry in recent years, the limitations of traditional aquaculture modes such as pond aquaculture, cofferdam aquaculture, and beach aquaculture have become increasingly prominent. Therefore, the high-efficiency and healthy northern suspension cage A. japonicus breeding model, with the best comprehensive benefits and the least management problems, came into being. Microorganisms, as an essential part of the aquaculture pond ecosystem, not only play an important role in the material circulation and energy flow of the ecosystem, but also have great significance in maintaining ecosystem balance. As a representative invertebrate, echinoderms such as A. japonicus have a simple digestive structure. Bacteria account for a large proportion of the gut microbiome of A. japonicus, providing more than 70% of their energy demand. The bacterial community is closely related to the healthy growth of the host and plays an important role in digestion and metabolism, defense against pathogens, and immune function. However, the complex bacterial community in the gut of aquaculture species depends on the culture environment, and there is a close symbiotic relationship between the environmental and gut bacterial community which affects the survival and growth of organisms, disease occurrence, and material circulation. Previous studies have shown that the complex bacterial community in the gut of A. japonicus primarily comes from their habitat and maintains a relatively stable dynamic balance with the external environmental community. In order to improve the growth capacity of A. japonicus and quality of the culture water, it is important to understand the structural characteristics of the bacterial communities of A. japonicus and their culture water to support the development of the A. japonicus aquaculture industry. This information will provide a theoretical reference for the healthy aquaculture of A. japonicus and assist with disease prevention and control. Clarifying the complex relationship between the structure and functional characteristics of bacterial communities and the aquaculture environment, as well as the important role of the bacterial community in growth, will support future research on the bacterial community mechanisms, explore ways to improve the ecological regulation of breeding yield, and promote the healthy development of the A. japonicus culture industry. To date, there have been limited studies on the correlation between the gut bacterial community structure of A. japonicus and its culture environment.At present, most of the existing studies are based on the traditional pure culture or separation and enrichment culture methods, which cannot accurately reflect natural bacterial communities. In recent years, high-throughput sequencing technology has introduced a new way to comprehensively analyze the structural and functional characteristics of bacterial communities by combining several bioinformatics methods. With the continuous development of molecular sequencing technology, 16S rRNA high-throughput sequencing technology has become a valuable tool to study the structure of bacterial communities. It has been widely used to study a variety of ecosystems and bacterial community diversity, providing a novel means to study the species diversity and quantity of bacterial communities, and the structural and functional characteristics of bacterial communities. Most of the relevant existing studies are based on the structure and diversity of the bacterial community of A. japonicus cultured in the south, whereas only a few studies have been conducted on the structure and functional characteristics of bacterial communities of A. japonicus cultured in suspension cages in the north. Therefore, in order to investigate the relationship between the bacterial community structure of A. japonicus and the culture water, this study analyzed their structural and functional characteristics in cage-cultured A. japonicus in North China using high-throughput sequencing technology, and preliminarily discussed the correlation between them. The results showed that the diversity and richness of the A. japonicus gut bacterial community were significantly higher than those of the culture water (P < 0.05). The dominant bacteria in the gut of A. japonicus and the culture water were Proteobacteria and Bacteroidetes. There were 13 common core bacteria with a relative abundance greater than 0.1%. In addition, the bacterial communities showed some independence; the specific phyla in the gut belonged to Firmicutes and Chloroflexi, represented by Bacillus, Lactobacillus, Halioglobus, Lutimonas, and Woeseia. Based on an analysis of the Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathway database, a total of 300 tertiary metabolic pathways was annotated, among which 146 tertiary metabolic pathways had highly significant differences (P < 0.001). The specific metabolic pathways in the gut of A. japonicus were mainly carbohydrate digestion and absorption, protein digestion and absorption, and sphingolipid metabolism. This study showed that the bacterial community in the gut of A. japonicus is similar to that of the culture water, but there were significant differences in the relative community abundance. The results of this study provide a theoretical basis for the healthy cultivation of northern A. japonicus in suspension cages.

Keywords

• apostichopus japonicus
• gut bacterial community
• suspension cage culture
• high-throughput sequencing
• community structure