Prokaryotes (2006) 1:475–507 DOI: 10.1007/0-387-30741-9_18 CHAPTER 2.5 Marine Marine Chemosynthetic Symbioses Marine Chemosynthetic Symbioses COLLEEN M. CAVANAUGH, ZOE P. MCKINESS, IRENE L.G. NEWTON AND FRANK J. STEWART Introduction ide or methane for carbon fixation and utiliza- tion. On the basis of these unique biosynthetic Bacteria and marine eukaryotes often coexist in capacities, notably the ability to synthesize C3 symbioses that significantly influence the ecol- compounds from C1 compounds, we refer collec- ogy, physiology and evolution of both partners. tively to these bacterial symbionts as “chemosyn- De Bary (1879) defined symbiosis as “the living thetic.” together of differently named organisms,” imply- Given the sulfide-rich habitats in which ing that the term encompasses both positive (e.g., chemoautotrophic symbioses occur, researchers mutualism) and negative (e.g., parasitism) asso- infer that the bacterial symbionts oxidize ciations. Many researchers now view symbiotic reduced inorganic sulfur compounds to obtain interactions as those that persist over the major- energy and reducing power for autotrophic car- ity of the lifespan of the organisms involved and bon fixation. While some endosymbionts (such as that provide benefits to each partner beyond those in the protobranchs Solemya velum and S. those obtained in the absence of association. This reidi; Cavanaugh, 1983; Anderson et al., 1987) µ chapter describes such symbioses, specifically utilize thiosulfate (S2O3 ), an intermediate in sul- those between marine invertebrate and protist fide oxidation, hydrogen sulfide is inferred to be hosts and chemosynthetic bacterial symbionts. the preferred energy source in a variety of sym- These bacteria, which cluster primarily within bioses (see review in Van Dover, 2000). But for the Gammaproteobacteria (Fig. 1), are chemo- many symbioses the actual energy source has not autotrophs or methanotrophs. In both chemo- been identified definitively; rather, only an autotrophic and methanotrophic symbioses, the autotrophic metabolism has been confirmed. hosts, through an astonishing array of physio- Indeed, chemosynthetic bacteria utilizing other logical and behavioral adaptations, provide the energy sources (e.g., hydrogen or ammonia) symbiont access to the substrates (i.e., electron could also serve similar nutritional roles in donors and acceptors) necessary for the genera- symbiotic associations. In this review, bacterial tion of energy and bacterial biomass. In symbionts that have been shown to use reduced µ µ2 µ o exchange, a portion of the carbon fixed by the sulfur compounds (H2S, HS , S , S2O3 , S ) for symbiont is used, either directly or indirectly, for energy metabolism are referred to as thio- host energy and biosynthesis. These symbioses autotrophs, while the more general term thereby increase the metabolic capabilities, and “chemoautotroph” is used to describe symbionts therefore the number of ecological niches, of for which data supporting autotrophic CO2 fixa- both the host and the bacterial symbiont. tion exist but for which the lithotrophic energy In those symbioses for which the electron source is unknown. donor has been explicitly identified, sulfide and other inorganic reduced sulfur compounds History (e.g., thiosulfate) fuel energy generation by the chemoautotrophic symbionts, serving as elec- The discovery of deep-sea hydrothermal vents tron sources for oxidative phosphorylation. In and the flourishing ecosystems associated with these symbioses, the ATP produced in electron them significantly advanced scientific under- transport fuels autotrophic CO2 fixation via the standing of chemosynthetic symbioses. Oceanog- Calvin cycle. In contrast, bacteria in marine raphers in the research submersible Alvin invertebrate-methanotroph symbioses use meth- discovered hydrothermal vents along the Gal- ane (CH4) as an energy, electron, and carbon apagos Rift in 1977. In stark contrast to percep- source. Unlike their protist or metazoan hosts, tions of the deep benthos as a cold, food-limited chemoautotrophs and methanotrophs share the habitat incapable of supporting substantial bio- ability to use reduced inorganic compounds or mass, hydrothermal vents are oases, charac- methane for energy generation and carbon diox- terized by high concentrations of free-living 476 C.M. Cavanaugh et al. CHAPTER 2.5 Chemoautotrophic symbionts: Mussel symbionts Vesicomyid clam symbionts Solemyid clam symbionts Lucinid clam symbionts Thyasirid clam symbionts Tubeworm symbionts Oligochaete symbionts Escherichia coli Nematode symbionts Coxiella burnetii Solemva reidi symbiont Methanotrophic symbionts GAMMA JTB254 Epsilon symbionts Achromatium oxaliferum 86 54 Inanidrilus leukodermatus symbiont 100 Olavius algarvensis gamma symbiont 65 Laxus sp symbiont Olavius loisae gamma symbiont 82 Solemva relum symbiont Solemva occidentalis symbiont Lucinella nassula symbiont Codakia orbicularis symbiont 97 98 Lucina floridana symbiont Chemoautotrophic 57 Codakia costata symbiont 68 Lucinoma annulata symbiont symbionts Lucinoma aequizonata symbiont 94 100 Ridgeia piscesae symbiont Rifna packyptria symbiont 100 Escorpia spicata symbiont Lamembrachia colmnua symbiont 93 64 Anodontia phillipiana symbiont 70 Solemya terraeregina symbiont 69 Thyasira flexuosa symbiont Solemya pusillu symbiont Lucina pectinata symbiont 80 Pseudomonas fluorescens 100 Pseudomonas putida 88 Pseudomonas lundensis 81 Pseudomonas fragi 100 Marinobacter sp CAB Marinobacter aquaeolei Oceanospirillum kriegii Thiothrix eikelboomii 100 52 98 Thiothrix unzii Thiothrix nivea Thiothrix ramosa Bathymodiolus japonicus symbiont 54 Methanotrophic 100 Bathymodiolus childressi symbiont Bathymodiolus platifrons symbiont symbionts 100 Bathymodiolus puteoserpentis symbiont 2 100 76 Methylobacter sp BB5.1 53 Methylococcus luteus 60 Methylococcus capsulatus BARH 61 Methyllobacter whittenburyi 100 Methylomonas aurantiaca Methylomonas rubra Methylococcus thermophilus GAMMA JTB35 100 Thiomicrospira sp. 82 Thiomicrospira crunogena 82 Thiomicrospira L12 100 Thiomicrospira milos T2 Thiomicrospira milos T1 69 100 Thiomicrospira thyasirae Thiomicrospira pelophila Maorithyas hadalis symbiont 1 Juan de Fuca mussel symbiont 55 Bathymodiolus septemdierum symbiont 52 70 Bathymodiolus thermophilus symbiont Bathymodiolus puteoserpentis symbiont 1 Bathymodiolus aff. brevior symbiont 62 Calyptogena magnifica symbiont Chemoautotrophic 100 Calyptogena fossajaponica symbiont 82 Calyptogena phaseoliformis symbiont symbionts Calyptogena FL sp. symbiont 94 Calyptogena pacifica symbiont 86 100 Vesicomya lepta symbiont 87 Vesicomya chordata symbiont 100 Calyptogena elongata symbiont 100 Calyptogena kilmeri symbiont Vesicomya gigas symbiont Ectenagena extenta symbiont Maorithyas hadalis symbiont 2 100 Halothiobacillus kellyi Halothiobacillus neapolitanus Non-gamma Olavius loisae alpha symbiont oligochaete Olavius loisae spirochete symbiont 100 Olavius algarvensis delta symbiont symbionts Desulfosarcina variabilis 100 84 Alvinella pompejana epibiont APB13B Alvinella pompejana epibiont APG44B Epsilon 87 Alvinella pompejana epibiont APG5B epibionts Rimicaris exoculata symbiont 100 Alvinella pompejana epibiont APG56B 100 Sulfurospirillum sp 18.1 Sulfurospirillum Am-N Fig. 1. Phylogeny showing the strict consensus of 46 trees obtained via parsimony analyses of 16S rRNA gene sequences (1456 bp) from symbiotic and free-living bacteria. Results greater than 50% from a 500 replicate bootstrap analysis are reported above respective branches. Chemosynthetic symbiont taxa are color-coded (see key on Figure). CHAPTER 2.5 Marine Chemosynthetic Symbioses 477 source for R. pachyptila, implying a role for chemoautotrophy in tubeworm metabolism. Following confirmation of a chemosynthetic endosymbiosis within the giant tubeworm, researchers questioned the putative reliance on filter feeding by other vent invertebrates. Ulti- mately, anatomical, enzymological, and isotopic analyses revealed the presence of sulfur- oxidizing bacterial symbionts either within the tissues (endosymbiotic) or attached to the sur- faces (episymbiotic) of most vent taxa, including vesicomyid clams, mytilid mussels, shrimp, and polychaete worms (Cavanaugh, 1994; Nelson and Fisher, 1995a; Van Dover, 2000). Recognizing the ubiquity of chemoau- totrophic symbioses at hydrothermal vents, researchers searched for and discovered similar symbiotic associations in other marine habitats, including coastal and subtidal reducing sedi- ments (e.g., Felbeck et al., 1981b; Southward et al., 1981; Southward, 1982; Cavanaugh, 1983; Giere, 1985; Bauer-Nebelsick et al., 1996), brine and hydrocarbon seeps (Sibuet and Olu, 1998), and whale skeletons (Bennet et al., 1994; Smith and Baco, 2003), thereby extending the host Fig. 2. Symbiont-containing host organisms from hydrother- taxa to include solemyid and lucinid bivalves, mal vents and cold seeps. (A) Calyptogena magnifica shell; pogonophoran tubeworms, echinoids and cili- courtesy of Emilio Jorge Power. (B) Filamentous bacteria on ates. In addition, methanotrophic bacteria were sulfide deposits from the East Pacific Rise. (C) Bathymodio- detected in a marine sponge (Vacelet et al., lus childressi from the Gulf of Mexico; courtesy of the 1995), a pogonophoran tubeworm (Schmaljo- National Oceanic and Atmospheric Administration. (D) Riftia pachyptila at the East Pacific Rise. hann and Flügel, 1987), and in vent and seep mussels, sometimes co-occurring with sulfur- oxidizing chemoautotrophs in a “dual symbiosis” microorganisms and dense aggregations of