or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of The approval portionthe ofwith any articlepermitted only photocopy by is of machine, reposting, this means or collective or other redistirbution This article has This been published in MOUNTAINS IN THE SEA Oceanography MICROBIOLOGY journal of The 23, Number 1, a quarterly , Volume OF SEAMOUNTS Common Patterns Observed in Community Structure O ceanography ceanography S BY DAVID EmERSON AND CRAIG L. MOYER ociety. © 2010 by The 2010 by O ceanography ceanography O ceanography ceanography ABSTRACT. Much interest has been generated by the discoveries of biodiversity InTRODUCTION S ociety. ociety. associated with seamounts. The volcanically active portion of these undersea Microbial life is remarkable for its resil- A mountains hosts a remarkably diverse range of unusual microbial habitats, from ience to extremes of temperature, pH, article for use and research. this copy in teaching to granted ll rights reserved. is Permission S ociety. ociety. black smokers rich in sulfur to cooler, diffuse, iron-rich hydrothermal vents. As and pressure, as well its ability to persist S such, seamounts potentially represent hotspots of microbial diversity, yet our and thrive using an amazing number or Th e [email protected] to: correspondence all end understanding of the microbiology of seamounts is still in its infancy. Here, we of organic or inorganic food sources. discuss recent work on the detection of seamount microbial communities and the Nowhere are these traits more evident observation that specific community groups may be indicative of specific geochemical than in the deep ocean. Much of the scenarios, such as iron and sulfur cycling. These observations are based on the deep seafloor consists of cold, relatively metabolisms predicted by phylogenetic characteristics exhibited by the dominant static sedimentary environments where populations found within these microbial communities as compared to the closest heterotrophic microbes exist in signifi- related isolate found in culture. Therefore, these studies combine the use of both cant numbers, but conditions remain O cultivation-dependent and -independent analyses. Cultivation-independent studies relatively unchanged over long periods ceanography were primarily completed using cloning and sequencing techniques targeting small of time. Mid-ocean ridges associated subunit ribosomal gene (SSU rDNA) biomarkers along with similar biomolecular with diverging plate boundaries are often S ociety, P ociety, tools like terminal-restriction fragment length polymorphism (T-RFLP) and sites of high-temperature hydrothermal O quantitative polymerase chain reaction (Q-PCR), which allow for the determination venting and host many chemoauto- B ox 1931, ox R of phylotypes (analogous to species). We discuss the notion of Zetaproteobacteria trophic microbes; however, these systems reproduction, systemmatic epublication, R and/or Epsilonproteobacteria being the most common members of hydrothermal are more homogeneous with respect ockville, M habitats associated with seamounts exhibiting volcanic activity. Another noneruptive to their physical and chemical proper- seamount scenario is also examined, for example, South Chamorro Seamount, an ties than vent systems associated with D 20849-1931, active forearc serpentinite mud volcano. volcanic arcs and backarcs (Takai et al., USA . 148 Oceanography Vol.23, No.1 2006), for example, seamounts. The volcanism driven by hotspots or mantle microbiology relevant to seamount enhanced heterogeneity of seamount- plumes within Earth’s crust (see Staudigel studies is the capacity for microbes to hosted hydrothermal systems repre- and Clague, 2010). The Hawaiian Islands live in the deep subsurface. The organic sents a dynamic range of habitats, in the Pacific Ocean and the Azores in and inorganic chemical reactions, as well providing for the growth of a remarkable the Atlantic Ocean are spectacular exam- as the geological processes associated diversity of microbes. ples of hotspots. Because our knowledge with microbial populations in the deep First and foremost, underwater about the role of seamounts as biogeo- subsurface biosphere, are interlinked, but volcanoes create seamounts, and the chemical foci for microbial activity is in little is known of the complexity of those intense volcanism at actively growing its infancy, it is instructive to consider linkages (Gold, 1992; Whitman et al., seamounts results in a variety of hydro- another seamount-associated microbial 1998). Furthermore, we are only begin- thermal vent environments. Although habitat that derives from fundamentally ning to realize both the phylogenetic these settings account for only a small different geological processes. diversity of microbes, and the extent of fraction of all seamounts, the hydro- The importance of hydrothermal their metabolic activities in these deep thermal venting offers the potential to vents associated with deep ocean crustal biosphere ecosystems. Drilling proj- fuel novel life forms. Older seamounts spreading centers as havens for microbial ects done in deep mines on land have that exhibit reduced volcanism, or are activity has fundamentally changed how revealed surprising microbial communi- dormant, may still be conduits for fluid we view life on Earth, and enlightened ties living kilometers below the surface exchange between the rock mantle our thinking about other places in and taking advantage of energy sources subsurface and the ocean (Wheat our solar system where life might also derived from interactions of water with et al., 2004). These fluids may also feed exist. The iconic features of these sites basement rock minerals (White et al., both deep subsurface and/or benthic are black smokers billowing super- 1998; Chivian et al., 2008). In the ocean, (bottom-dwelling) microbial communi- heated water charged with iron sulfide deep-sea drilling into old sediments ties (Cowen et al., 2003; Huber et al., minerals, as well as dense communi- has revealed bacteria and archaea living 2006). Finally, even dormant seamounts ties of macrofauna largely fueled by up to hundreds of meters below the that rise to appreciable depths above the symbiotic relationships with bacteria seafloor (Parkes et al., 2000; Jørgensen ocean floor (i.e., > 1000 m) can impact that provide energy for their hosts using and Boetius, 2007). The extent of micro- ocean currents and mixing, potentially sulfide-rich waters emanating from the organisms living in oceanic crust is less resulting in stimulation of microbial vents. The discovery of these deep-sea well understood because drilling into communities that feed off the enriched ecosystems has reshaped our thinking and recovering good samples from hard, nutrients (see Lavelle and Mohn, 2010). and research agenda regarding extreme fractured rock is much more challenging This latter possibility applies to active oases of life in the deep sea. Some of the than from ocean sediments. Here, seamounts as well. most notable findings from over three seamounts constitute an opportunity There are estimated to be over decades of research on hydrothermal for future studies. First, they represent 100,000 seamounts that reach a kilometer vents are the extension of the thermal extensions of Earth’s crust above the or more above the seafloor (see Wessel limit for life (Takai et al., 2008) as well seafloor, in essence making basement et al., 2010). This large number illustrates as the discovery of a host of bacteria rocks more available for sampling. the potential scope of seamounts to and archaea with novel anaerobic and Second, seamounts may act as perme- provide and impact habitats for marine aerobic metabolisms that take advantage able conduits for exchange of fluids microbes. The majority of seamounts are of unique suites of energy sources (both between the ocean and oceanic crust associated with tectonic processes taking autotrophic and heterotrophic) derived (see Fisher and Wheat, 2010). Could place in Earth’s crust, for example, island from the combination of geochemistry, it be that seamounts represent a new arcs that have chains of undersea moun- temperature, and pressure at these sites frontier for making discoveries about tains that result from converging plates. (Karl, 1995; Nakagawa and Takai, 2008). the diversity and abundance of microbial Another source of seamounts is undersea Another emerging aspect of life in the ocean? Oceanography March 2010 149 SIZING Up SEAMOUNT active hydrothermal venting at young 24 seamounts (Table 1). By comparison, MICROBIOLOGY WITH seamounts (Emerson and Moyer, 2002; there have been hundreds of papers A MICROBIAL TOUR OF Edwards et al., 2005; Templeton et al., investigating the different aspects of SEAMOUNTS 2009). Thus, active submarine-arc the microbiology of seafloor spreading Seawater circulation through the oceanic volcanoes typify hydrothermal systems centers. Nonetheless, this work illustrates crust aided by seamount-supported that provide abundant nutrient-rich the diversity of habitats that may exist at permeable pathways is conducive to fluids on which microbial communities seamounts, which, in turn, illustrates the microbiological activity because of can live and grow (Figure 1). However, variety of geochemical and hydrological the large amounts of nutrient-rich surprisingly little is known about the conditions that make many seamounts fluids that flow through these relatively microbiology