Gill chamber and gut microbial communities of the hydrothermal shrimp Rimicaris chacei Williams and Rona 1986: A possible symbiosis

Rimicaris chacei Williams and Rona 1986, formerly named as Chorocaris chacei, is a caridean shrimp living in deep-sea hydrothermal ecosystems. This shrimp is endemic to the Mid Atlantic Ridge (MAR) and lives at the periphery of aggregates of its well-known congeneric R. exoculata Williams and Rona 1986. Contrasting with the very dense and mobile clusters formed by R. exoculata, R. chacei lives in small groups of several individuals that are not very mobile. Although devoid of the characteristic hypertrophied cephalothorax of R. exoculata, which harbors the ectosymbionts, a microbial community has also been reported in the cephalothorax of R. chacei. Previous data on morphology, behavior and isotopic values indicate a diet based on a combination of feeding on its epibiotic bacteria and scavenging or occasional predation. In this study, our objective was to describe, for the first time, the distribution, morphology and phylogeny of the microbial communities associated with R. chacei. This species is significantly less studied than R. exoculata, but nevertheless represents the only other known example of symbiosis in crustaceans of MAR hydrothermal vent sites. Microbial communities have been observed at the same locations as in R. exoculata (mouthparts, branchiostegites and digestive tract). However, in R. chacei, the surfaces occupied by the bacteria are smaller. The main lineages are affiliated to Epsilon and Gammaproteobacteria in the cephalothorax and to Deferribacteres, Mollicutes, Epsilon and Gammaproteobacteria in the digestive tract. Comparison with the well-described bacterial communities of R. exoculata and hypotheses about the role of these communities in R. chacei are discussed.