Occurrence of Aeromonas Species in the Cutaneous Mucus of Barbour's Seahorses (Hippocampus barbouri) as Revealed by High-Throughput Sequencing

Abstract

Although several studies have described the bacterial community composition associated with marine fish, there is limited information related to seahorses. Moreover, previous studies have demonstrated that the skin microbiota is useful for determining health status and common disorders in the host. This study, therefore, aimed to explore the skin bacterial community composition in Barbour's seahorse (Hippocampus barbouri) using high-throughput sequencing of 16S ribosomal RNA genes. Water and sediment samples from the surrounding environment were also analyzed for comparative purposes. The results revealed that sequences affiliated with the Shewanellaceae family were dominant in the skin of female Barbour's seahorses and sediment samples, whereas sequences affiliated with the Bacillaceae family were dominant in the skin of male Barbour's seahorses. Interestingly, sequences affiliated with the Aeromonas genus were found in the skin of Barbour's seahorses, whose abundance was slightly similar between the female and male specimens. Further comparative analysis showed that the presence of Aeromonas species in the skin of Barbour's seahorses was strongly influenced by the surrounding sediment. Given that some Aeromonas species are known to be important pathogens in humans and fish, these results may be used for further research on the dependency of the skin microbial composition on the environment as well as determine whether the presence of Aeromonas and other detected species has implications on seahorse health.

Keywords: Aeromonas species; H. barbouri; Illumina sequencing; marine microorganisms; seahorse.

Figure 1

(A) Relative abundance of dominant bacterial families found in the skin samples from Barbour’s seahorses as well as in water and sediment samples from the surrounding environment. (B) Phylogenetic dendrogram of selected OTUs with the most closely related Aeromonas species based on 16S rRNA gene sequences (420 bp) and constructed by the neighbor-joining method. Bootstrap percentages (>50%) based on 1000 replications are shown at branch nodes. Bar, 0.002 estimated substitutions per site.

Figure 2

Heatmap of OTUs assigned to the Aeromonadaceae family, which were compared with their abundances in each sample. The color intensity (log2 scale) in each panel shows the percentage of each OTU.