Characterization of Symbiont Populations in Life-History Stages of Mussels From Chemosynthetic Environments

Abstract

The densities of chemoautotrophic and methanotrophic symbiont morphotypes were determined in life- history stages (post-larvae, juveniles, adults) of two species of mussels (Bathymodiolus azoricus and B. heckerae) from deep-sea chemosynthetic environments (the Lucky Strike hydrothermal vent and the Blake Ridge cold seep) in the Atlantic Ocean. Both symbiont morphotypes were observed in all specimens and in the same relative proportions, regardless of life-history stage. The relative abundance of symbiont morphotypes, determined by transmission electron microscopy, was different in the two species: chemoautotrophs were dominant (13:1-18:1) in B. azoricus from the vent site; methanotrophs were dominant (2:1-3:1) in B. heckerae from the seep site. The ratio of CH4:H2S is proposed as a determinant of the relative abundance of symbiont types: where CH4:H2S is less than 1, as at the Lucky Strike site, chemoautotrophic symbionts dominate; where CH4:H2S is greater than 2, as at the seep site, methanotrophs dominate. Organic carbon and nitrogen isotopic compositions of B. azoricus (delta 13C = -30 per thousand; delta 15N = -9 per thousand) and B. heckerae (delta 13C = -56 per thousand; delta 15N = -2 per thousand) varied little among life-history stages and provided no record of a larval diet of photosynthetically derived organic material in the post-larval and juvenile stages.

Influence of CH<sub>4</sub> and H<sub>2</sub>S availability on symbiont distribution, carbon assimilation and transfer in the dual symbiotic vent mussel <i>Bathymodiolus azoricus</i>

“…This supports the hypothesis that symbiont populations react to changes in environmental parameters, in particular to the balance between sulphide and methane, and thus optimize the use of available compounds as suggested by previous authors (Trask and Van Dover, 1999;Colaço et al, 2002a;Salerno et al, 2005;Duperron et al, 2007). The range of variation observed in symbiont relative abundances, with MOB occupying between 4 and 39% of total bacterial area in specimens of this study (Table 3), confirms the high level of plasticity of the dual symbiosis.…”

“…MAR vent sites (Sarradin et al, 1998). Methane was bubbled continuously in seawater and dissolved methane concentration was monitored by sampling 60 mL seawater in a 300 mL bottle which was rolled for 20 min before measuring the headspace CH 4 concentration with a Gasurveyor 524.…”

An overview of chemosynthetic symbioses in bivalves from the North Atlantic and Mediterranean Sea

“…In the Mytilidae, many authors suggest that symbiont uptake occurs early in life (Fig. 4b, Salerno et al, 2005). However, repeated observations of abundant endocytosis vacuoles engulfing bacteria in adult gill epithelial cells suggest that symbiont uptake may also occur in adults (Dubilier et al, 1998;Fiala-Médioni et al, 2002).…”

Next Generation Sequencing and Microbial Community Associated With Eukaryotes Including Parasitic Heliminths: A Review Article.

“…Such free-living populations occur in soil [77], marine shallow waters and the deep sea [78]. In some cases the free-living population is restored by symbiont release from the host [79]. Vertical transmission frequently involves no aposymbiotic phase and transmission through the female germ line, even though there may be acquiring during mating.…”