Abstract
Recently, Streptococcus agalactiae has become a major pathogen leading to Streptococcosis. To understand the physiological responses of zebrafish (Danio rerio) to S. agalactiae, the intestinal microbiota composition of the intestine (12 and 24 h post-infection, hpi, respectively) in zebrafish infected with S. agalactiae were investigated. The intestinal bacterial composition was analyzed using PacBio high-throughput full-length 16S rRNA gene sequencing. The most predominant bacteria in the zebrafish intestine were the Fusobacteria phylum and Sphingomonas genus. S. agalactiae infection affected the composition of partially intestinal microbiota. At the species level, the relative abundance of the pathogenic intestinal bacteria Aeromonas veronii, S. agalactiae, and Clostridium tarantellae significantly increased after S. agalactiae infection (p < 0.05), while that of the beneficial intestinal bacteria Bacillus licheniformis, Comamonas koreensis, and Romboutsia ilealis significantly decreased (p < 0.05), showing that S. agalactiae infection aggravates the zebrafish disease through promoting abundance of other intestinal pathogenic bacteria. This study is the first PacBio analyses of the zebrafish intestinal microbiota community under pathogenic infection. Results suggest that the S. agalactiae infection alters the intestinal flora structure in zebrafish.
Highlights
Streptococcus agalactiae is a Gram-positive bacterium belonging to group B Streptococcus
By comparing average length of 16S rRNA gene sequences to those from previous studies of intestinal microbiota communities analyzed by Illumina sequencing technology (∼349–400 bp) (Zheng et al, 2019), there is an obvious advantage in terms of the read lengths generated by Pacific Biosciences (PacBio)
This study shows the first high-throughput analysis of the intestinal microbiota structure in fish after bacterial infection using PacBio full-length 16S rRNA gene sequencing technology
Summary
Streptococcus agalactiae is a Gram-positive bacterium belonging to group B Streptococcus. S. agalactiae infection can cause a variety of fish diseases, such as meningitis, sepsis, ascites, and anorexia, leading to extremely high mortality rates, generally greater than 50% (Su et al, 2016). Tilapia (Oreochromis niloticus) is reported to be under the greatest threat from S. agalactiae infection. S. agalactiae infection occurs frequently in the main tilapia production areas in China, with an incidence rate greater than 90%, and a cumulative mortality rate of up to 90% (Li et al, 2009; Xing et al, 2011). S. agalactiae has a wide range of hosts and a long duration of infection and can cause high mortality rates in fish, leading to a serious threat for the healthy development of the fishery industry
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