Bacterial ectosymbionts colonizing gills of two Caribbean mangrove crabs

We describe here the interactions between bacterial ectosymbionts and two Caribbean mangrove crabs: Aratus pisonii (Sesarmidae) and Minuca rapax (Ocypodidae). Specimens of A. pisonii and M. rapax were collected in Guadeloupe from mangrove trees (Rhizophora mangle) and from the mangrove mud, respectively. Ectosymbionts colonizing gills in all host individuals were observed using scanning and transmission electron microscopy (SEM and TEM). No intracellular bacteria were observed in gills cells suggesting that the biofilm only occurs on the surface of the gills. For A. pisonii and M. rapax, four different bacterial morphotypes were distributed throughout the surface of gill lamellae. Different sizes and lengths were observed in the bacterial population colonizing A. pisonii and M. rapax. Either symbionts cover the entire surface of the gills, or they formed irregularly distributed patches. Molecular analyses (high-throughput amplicon sequencing of bacterial 16S rRNA-encoding genes) confirmed the occurrence of multiple bacterial taxonomic units, with dominance of Alphaproteobacteria and Bacteroidetes in both host species. However, dominant bacterial phylotypes were not shared between A. pisonii and M. rapax. This suggests that each species of these semiterrestrial crabs may harbor a specific and distinct bacterial community despite living in the same mangroves. The discussion compares the bacterial compositions of the two species and their potential functions are hypothesized. Further investigations are needed to confirm the specificity and nature of the symbiosis, including potential exchanges occurring between the partners.

Automated summary

This study investigates the interactions between bacterial ectosymbionts and two Caribbean mangrove crabs, showing that different bacterial morphotypes colonize the gills of Aratus pisonii and Minuca rapax. Molecular analysis revealed the dominance of Alphaproteobacteria and Bacteroidetes in both host species, with specific bacterial phylotypes not shared between the two crab species. Further investigations are needed to confirm the specificity and nature of the symbiosis.