Symbiotic Bacteria in Gills and Guts of Chinese Mitten Crab (Eriocheir sinensis) Differ from the Free-Living Bacteria in Water

Abstract

Aquatic animals have a close relationship with water, but differences in their symbiotic bacteria and the bacterial composition in water remains unclear. Wild or domestic Chinese mitten crabs (Eriocheir sinensis) and the water in which they live were collected from four sampling sites in Jiangsu and Shanghai, China. Bacterial composition in water, gills or guts of E. sinensis, were compared by high-throughput sequencing using 16S rRNA genes. Analysis of >660,000 sequences indicated that bacterial diversity was higher in water than in gills or guts. Tenericutes and Proteobacteria were dominant phyla in guts, while Actinobacteria, Proteobacteria and Bacteroidetes were dominant in gills and water. Non-metric multidimensional scaling analysis indicated that microbiota from gills, guts or water clearly separated into three groups, suggesting that crabs harbor a more specific microbial community than the water in which they live. The dominant OTUs in crab gut were related to Mycoplasmataceae, which were low in abundance in gills, showing that, like mammals, crabs have body-site specific microbiota. OTUs related to Ilumatobacter and Albimonas, which are commonly present in sediment and seawater, were dominant in gills but almost absent from the sampled water. Considering E. sinensis are bottom-dwelling crustacean and they mate in saline water or seawater, behavior and life cycle of crabs may play an important role in shaping the symbiotic bacterial pattern. This study revealed the relationship between the symbiotic bacteria of Chinese mitten crab and their habitat, affording information on the assembly factors of commensal bacteria in aquatic animals.

Fig 1. Frequency distribution of bacterial phyla in water, gills and guts.

Similarity among samples was calculated using the Bray-Curtis method.

Fig 2. NMDS plot showing microbial community differences in water, gills and guts.

The distances were determined using the Bray-Curtis method with relative abundance of OTUs. Green represents samples from site T, yellow samples from site S, blue samples from Y, and red samples from C. Diamonds indicate samples from water, triangles samples from gut, and circles samples from gills.

Fig 3. Heatmap analysis of the OTUs in all samples.

The color of the bar represents the abundance of each OTU in a given sample. The affiliation of each OTU is indicated on the right.

Fig 4. Network analysis visualizing the unique and shared bacterial groups in guts and gills of Chinese mitten crab and in the water in which they live.

Node sizes correspond to the mean relative abundance of each bacterial group. The proportion of shared bacteria is represented by the different colors in the pie charts; if the proportion of the bacterial group is <0.1% in gill, gut or water, these bacterial groups are shown with a line only.