Is It First the Egg or the Shrimp? – Diversity and Variation in Microbial Communities Colonizing Broods of the Vent Shrimp Rimicaris exoculata During Embryonic Development

Abstract

Rimicaris exoculata is one of the most well-known and emblematic species of endemic vent fauna. Like many other species from these ecosystems, Rimicaris shrimps host important communities of chemosynthetic bacteria living in symbiosis with their host inside the cephalothorax and gut. For many of these symbiotic partners, the mode of transmission remains to be elucidated and the starting point of the symbiotic relationship is not yet defined, but could begin with the egg. In this study, we explored the proliferation of microbial communities on R. exoculata broods through embryonic development using a combination of NGS sequencing and microscopy approaches. Variations in abundance and diversity of egg microbial communities were analyzed in broods at different developmental stages and collected from mothers at two distinct vent fields on the Mid-Atlantic Ridge (TAG and Snake Pit). We also assessed the specificity of the egg microbiome by comparing communities developing on egg surfaces with those developing on the cuticle of pleopods, which are thought to be exposed to similar environmental conditions because the brood is held under the female’s abdomen. In terms of abundance, bacterial colonization clearly increases with both egg developmental stage and the position of the egg within the brood: those closest to the exterior having a higher bacterial coverage. Bacterial biomass increase also accompanies an increase of mineral precipitations and thus clearly relates to the degree of exposure to vent fluids. In terms of diversity, most bacterial lineages were found in all samples and were also those found in the cephalothorax of adults. However, significant variation occurs in the relative abundance of these lineages, most of this variation being explained by body surface (egg vs. pleopod), vent field, and developmental stage. The occurrence of symbiont-related lineages of Epsilonbacteraeota, Gammaproteobacteria, Zetaproteobacteria , and Mollicutes provide a basis for discussion on both the acquisition of symbionts and the potential roles of these bacterial communities during egg development.

Antimicrobial Peptides and Ectosymbiotic Relationships: Involvement of a Novel Type IIa Crustin in the Life Cycle of a Deep-Sea Vent Shrimp

“…The transcriptomic and protein levels of Re-crustin were investigated at different stages of the shrimp life-cycle for which the colonization states by the ectosymbionts were already described (Figure 7) (5,47). In late eggs, when they are covered by large amount of symbionts (47), the gene is slightly expressed (Figure 7A), but the protein is not detected in the western blot analysis (Figure 7B).…”

“…The transcriptomic and protein levels of Re-crustin were investigated at different stages of the shrimp life-cycle for which the colonization states by the ectosymbionts were already described (Figure 7) (5,47). In late eggs, when they are covered by large amount of symbionts (47), the gene is slightly expressed (Figure 7A), but the protein is not detected in the western blot analysis (Figure 7B). Using immunohistochemistry, which is a more sensitive method, we detect a small amount of the protein in the membrane of freshly spawned eggs (early eggs, almost deprived of symbionts, Methou et al (47) (Figures 8A,B).…”

“…In late eggs, when they are covered by large amount of symbionts (47), the gene is slightly expressed (Figure 7A), but the protein is not detected in the western blot analysis (Figure 7B). Using immunohistochemistry, which is a more sensitive method, we detect a small amount of the protein in the membrane of freshly spawned eggs (early eggs, almost deprived of symbionts, Methou et al (47) (Figures 8A,B). In late stages, Re-crustin was immunodetected into vesicles beneath the cell membrane (Figures 8CA,D) and on the bacteria that form the biofilm surrounding the eggs (Figures 8CB,D).…”

“…Then, we investigated expression patterns in different host tissues and throughout its life cycle in order to identify possible correlations with the main symbiosis related events taking place at different life stages of this vent shrimp. These events include embryonic development (5,47), juvenile settlement into adult habitats (P. Methou, personal communication), and through the molt cycle involving re-establishment of the symbiotic community after each molting event (39).…”

Rimicaris exoculata: biology and ecology of a shrimp from deep-sea hydrothermal vents associated with ectosymbiotic bacteria

“…When present, larvae are also aposymbiotic during their pelagic dispersal (Bright & Bulgheresi 2010). To date, no bacteria have been observed inside eggs of R. exoculata, but Gammaproteobacteria and Campylobacteria have been reported on their surface (Guri et al 2012, Cowart et al 2017, Methou et al 2019). In the same way, bacterial symbionts appear to be absent in the branchial chamber of post-hatching larvae of R. exoculata (Guri et al 2012, Hernandez-Avila et al 2015 or in their first juvenile stages after recruitment (Komai & Segonzac 2008).…”