Acquisition of epibiotic bacteria along the life cycle of the hydrothermal shrimp Rimicaris exoculata

Abstract

The caridean shrimp Rimicaris exoculata dominates the fauna at several Mid-Atlantic Ridge hydrothermal vent sites. This shrimp has an enlarged gill chamber, harboring a dense ectosymbiotic community of chemoautotrophic bacteria associated with mineral oxide deposits. Until now, their acquisition is not fully understood. At three hydrothermal vent sites, we analyzed the epibionts diversity at different moult stages and also in the first stages of the shrimp life (eggs, hatched eggs (with larvae) and juveniles). Hatched eggs associated with young larvae were collected for the first time directly from gravid females at the Logachev vent site during the Serpentine cruise. An approach using 16S rRNA clone libraries, scanning and transmission electron microscopy, and fluorescent in situ hybridization was used. Molecular results and microscope observations indicated a switch in the composition of the bacterial community between early R. exoculata life cycle stage (egg libraries dominated by the Gammaproteobacteria) and later stages (juvenile/adult libraries dominated by the Epsilonproteobacteria). We hypothesized that the epibiotic phylotype composition could vary according to the life stage of the shrimp. Our results confirmed the occurrence of a symbiosis with Gammaproteobacteria and Epsilonproteobacteria, but more complex than previously assumed. We revealed the presence of active type-I methanotrophic bacteria colonizing the cephalothorax of shrimps from the Rainbow site. They were also present on the eggs from the Logachev site. This could be the first 'epibiotic' association between methanotrophic bacteria and hydrothermal vent crustacean. We discuss possible transmission pathways for epibionts linked to the shrimp life cycle.

Inorganic carbon fixation by chemosynthetic ectosymbionts and nutritional transfers to the hydrothermal vent host-shrimp Rimicaris exoculata

“…That the presence of an electron donor increases the carbon fixation rate indicates that Na 2 S 2 O 3 , and Fe 2 þ at least contribute to fuelling R. exoculata epibionts, and our autoradiography data suggest that chemosynthesis occurs at least in the large filamentous bacteria (epsilonproteobacteria of Marine Group 1), which appeared more intensely labelled than the thin filamentous and rod-shaped ones (epsilonproteobacteria of Marine Group 2 and gammaproteobacteria). The view that R. exoculata epibionts have sulphide-oxidising activity is consistent, moreover, with the fact epsilon-and gammaproteobacteria are assumed to have such activity, on the basis of the group affiliation of the former (Petersen et al, 2009;Goffredi, 2010;Guri et al, 2012) and because the latter possess functional SoxB and aprA genes (Hü gler et al, 2010(Hü gler et al, , 2011. We cannot say, however, what the epibiotic bacteria of R. exoculata use as predominant energy source.…”

“…Authors have also identified gamma-proteobacterial epibionts of the Thiotrichaceae family (Leucothrix group), together with some free-living members and some other invertebrate ectosymbionts, mainly of crustaceans (Goffredi, 2010). These gammaproteobacteria appearing at least as filamentous and rod-shaped morphotypes can probably grow as sulphide oxidisers, most likely using the APS pathway for energy generation and the Calvin-Benson-Bassham cycle for carbon fixation (aprA and cbbM gene sequences, respectively) (Zbinden et al, 2008;Hü gler et al, 2010Hü gler et al, , 2011Guri et al, 2012). In addition, coccoidshaped cells with intracytoplasmic membrane stacks have been identified as type-I methanotrophic gammaproteobacteria (pmoA gene sequence) (Corbari et al, 2008a;Zbinden et al, 2008;Guri et al, 2012), and deltaproteobacteria related to Desulfocapsa have been identified thanks to their aprA and hydrogenase gene sequences (Hü gler et al, 2011), suggesting they can grow lithotrophically using hydrogen as electron donor for sulphate reduction.…”

“…By combining 16S rRNA and functional gene analysis with in-situ hybridisation and transmission electron microscopy observations on R. exoculata epibionts and their free-living or symbiotic relatives from vent habitats, investigators (Campbell et al, 2006;Zbinden et al, 2008;Petersen et al, 2009;Goffredi, 2010;Hü gler et al, 2010Hü gler et al, , 2011Guri et al, 2012) have evidenced epsilonproteobacteria of Marine Groups 1 (the new family Thiovulgaceae) and 2, as thick (3-mm wide) and thin (1-mm wide) filaments, respectively. Both should oxidise sulphur compounds through the Sox pathway and fix carbon through the reverse tricarboxylic acid cycle (SoxB and aclA gene sequences).…”

“…These gammaproteobacteria appearing at least as filamentous and rod-shaped morphotypes can probably grow as sulphide oxidisers, most likely using the APS pathway for energy generation and the Calvin-Benson-Bassham cycle for carbon fixation (aprA and cbbM gene sequences, respectively) (Zbinden et al, 2008;Hü gler et al, 2010Hü gler et al, , 2011Guri et al, 2012). In addition, coccoidshaped cells with intracytoplasmic membrane stacks have been identified as type-I methanotrophic gammaproteobacteria (pmoA gene sequence) (Corbari et al, 2008a;Zbinden et al, 2008;Guri et al, 2012), and deltaproteobacteria related to Desulfocapsa have been identified thanks to their aprA and hydrogenase gene sequences (Hü gler et al, 2011), suggesting they can grow lithotrophically using hydrogen as electron donor for sulphate reduction. On this basis, the authors hypothesise that an internal sulphur cycle between sulphur-oxidising epsilon-and gammaproteobacteria and sulphate-reducing deltaproteobacteria could take place in the shrimp gill chamber, as proposed for oligochete symbiosis (Dubilier et al, 2001).…”

“…The shrimp R. exoculata, listed as a model organism of an extreme deep-sea environment (CAREX, 2010), is exceptional among crustaceans for its association with bacteria. Recent studies suggest that R. exoculata gill chamber epibionts constitute a diversified community with various morphotypes, phylotypes and metabolisms (Zbinden et al, 2004(Zbinden et al, , 2008Petersen et al, 2009;Hü gler et al, 2011;Guri et al, 2012), but no study has directly demonstrated which substrate(s) the bacteria oxidise to fuel their 'chemosynthetic' metabolism(s). This shrimp also harbours a digestive bacterial community (Zbinden and Cambon-Bonavita, 2003;Durand et al, 2010) whose role remains hypothetical (detoxification, nutrition and/or pathogen control).…”