[Show abstract][Hide abstract] ABSTRACT: Many recent studies have shown that submarine basaltic rocks can host a diverse, well-developed microbial community and yet the ocean crust has been shown to be extremely oligotrophic, especially below its surface. This study demonstrates that iron-oxidizing and -reducing bacterial strains, isolated from Loihi Seamount off the southeast coast of the Big Island of Hawai'i, are able to utilize different nutrients (phosphate), electron donors (reduced iron as Fe(II)) and electron acceptors (oxidized iron as Fe(III)) found within basaltic glasses. To test whether microbial life is able to acquire specific required nutrients and energy sources directly from basaltic substrates under nutrient-limiting conditions, we prepared three different basaltic glass substrates: one amended with increased levels of phosphate (apatite), one with predominantly Fe(III) and one with predominantly Fe(II) and exposed these glasses in an annular reactor to a suite of metal-oxidizing and reducing isolates and a microbial mat consortium. Lithoautotrophic growth of Pseudomonas LOB-7, an obligate Fe(II)-oxidizing bacterium, was found on all basaltic substrates in excess of that found on a background borosilicate glass, while enhanced growth was observed on the apatite infused glass over other basaltic substrates when phosphate was absent in the growth medium. Anaerobic, heterotrophic growth of Shewanella 601R-1 with lactate revealed an 2x increase in cell growth on the Fe(III)-enriched basalt. A parallel experiment performed using a natural inoculum from a Fe(III)-rich microbial mat revealed enhanced growth on all basalt surfaces over the background borosilicate glass. These results indicate that the chemical composition of basaltic substrates likely plays an important role in microbial colonization and enhanced growth under minimal nutrient conditions.
[Show abstract][Hide abstract] ABSTRACT: We present an interlaboratory comparison between full-length 16S rRNA gene sequence analysis and terminal restriction fragment length polymorphism (TRFLP) for microbial communities hosted on seafloor basaltic lavas, with the goal of evaluating how similarly these two different DNA-based methods used in two independent labs would estimate the microbial diversity of the same basalt samples. Two samples were selected for these analyses based on differences detected in the overall levels of microbial diversity between them. Richness estimators indicate that TRFLP analysis significantly underestimates the richness of the relatively high-diversity seafloor basalt microbial community: at least 50% of species from the high-diversity site are missed by TRFLP. However, both methods reveal similar dominant species from the samples, and they predict similar levels of relative diversity between the two samples. Importantly, these results suggest that DNA-extraction or PCR-related bias between the two laboratories is minimal. We conclude that TRFLP may be useful for relative comparisons of diversity between basalt samples, for identifying dominant species, and for estimating the richness and evenness of low-diversity, skewed populations of seafloor basalt microbial communities, but that TRFLP may miss a majority of species in relatively highly diverse samples.
[Show abstract][Hide abstract] ABSTRACT: Studies of the oceanic crust over the past decade have revealed that in spite of the oligotrophic nature of this environment, a diverse biosphere is present in the upper 1 km of basaltic crust. The key energy source in this setting may be the high content of transistion metals (Fe, Mn) found in the basaltic glass, but in order to discover the role of Fe and Mn in the deep biosphere, we must first determine which microbes are present and how they attain the necessary metabolites for proliferation. Our work contributes to both questions through the use of molecular microbiology techniques and the exposure of specifically designed substrates on the ocean floor. Loihi Seamount off the southeast coast of the Big Island of Hawai'i provides a unique laboratory for the study of distribution and population of microbial communities associated with iron rich environments on the ocean floor. Iron oxide flocculent material (floc) dominates the direct and diffuse hydrothermal venting areas on Loihi which makes it a prime target for understanding the role of iron in biological systems in the deep biosphere. We collected iron oxide floc and basaltic glass from pillow basalts around several hydrothermal vents on the crater rim, within the pit crater Pele's Pit, and from deep off of the southern rift zone of Loihi using the HURL PISCES IV/V submersibles. We also deployed basaltic glass sand amended with various nutrients (phosphate, oxidized and reduced iron, manganese) and recovered them in subsequent years to determine how substrate composition affects community structure. We extracted DNA from both rock and iron flocs and used t-RFLP to obtain a genetic fingerprint of the microbial communities associated with each substrate. From olivine and tholeiitic basalt enrichments, it appears that substrate composition strongly influences microbial colonization and subsequent community development even when deployed in the same conditions. Culturing efforts have yielded several iron metabolizing isolates which are able to grow with basalt as their only source of phosphate and electron donors and acceptors, which indicates that they are capable of leeching nutrients required for metabolism directly from the rock surface. Characterizing these chemolithoautotrophic microbes and the environments in which they are found can dramatically increase our understanding of the breadth and significance of the biosphere as it pertains to global seawater and ocean crust element cycling.
[Show abstract][Hide abstract] ABSTRACT: The element Fe and Fe-bearing minerals occur ubiquitously throughout the field of astrobiology. Cycling between the various oxidation states of Fe provides a source of energy available for life. Banded iron formations may record the rise of oxygenic photosynthesis. The distribution of Fe between Fe-bearing minerals and its oxidation states can help to characterize and understand ancient environments with respect to the suitability for life by constraining the primary rock type and the redox conditions under which it crystallized, the extent of alteration and weathering, the type of alteration and weathering products, and the processes and environmental conditions for alteration and weathering. Fe Mössbauer spectroscopy is a powerful tool to investigate Fe-bearing compounds. It can identify Fe-bearing minerals, determine Fe oxidation states with high accuracy, quantify the distribution of Fe between mineralogical phases, and provide clues about crystallinity and particle sizes. Two miniaturized Mössbauer spectrometers are on board of the NASA Mars Exploration Rovers Spirit and Opportunity. The Fe-bearing minerals goethite, an iron oxide-hydroxide, and jarosite, an iron hydroxide sulfate, were identified by Mössbauer spectroscopy in Gusev Crater and at Meridiani Planum, respectively, providing in situ proof of an aqueous history of the two landing sites and constraints on their habitability. Hematite identified by Mössbauer spectroscopy at both landing sites adds further evidence for an aqueous history. On Earth, Mössbauer spectroscopy was used to monitor possibly microbially-induced changes of Fe-oxidation states in basaltic glass samples exposed at the Loihi Seamount, a deep sea hydrothermal vent system, which might be analogous to possible extraterrestrial habitats on ancient Mars or the Jovian moon Europa today.
Planetary and Space Science 01/2006; · 2.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Mn is a trace component of volcanic rocks that is commonly enriched by 1-2 orders of magnitude within the secondary mineral assemblages associated with submarine basalts. Our analysis of relatively young basalts recovered from active seamounts such as Loihi Seamount (Hawaii) and Vailulu'u Seamount (American Samoa) shows that Mn(IV)-oxides readily form during short time-periods (10 years) of low-temperature (~2C) alteration, although the abiotic kinetics of Mn(II)-oxidation are slow at this temperatures and pH. We suggest that the formation of these secondary minerals are likely due to the common presence of heterotrophic bacteria with the functional capability of Mn(II)-oxidation, which accelerate the rates of oxidation several orders of magnitude faster than predicted for water-rock interaction alone. To identify and isolate endolithic Mn(II)-oxidizing microorganisms from naturally-weathered basalt surfaces, samples were recovered from the cold outer-flanks of Loihi and Vailulu'u Seamount via submersible with a sealable biobox. Using a variety of oligotrophic to organic-rich seawater-based media, we have isolated over 40 strains of Mn(II)-oxidizing bacteria. These isolates are primarily alpha- and gamma-Proteobacteria that can grow on low concentrations of simple to complex organics, but not Mn(II) as a sole energy source. None of the isolates, nor their closest relatively, were previously recognized as Mn(II)-oxidizing bacteria. In particular, we have found that there are several strains that are common to the basalts recovered from Loihi & Vailulu'u Seamount, as well as from basalts collected at the East Pacific Rise, particularly Pseudoalteromonas and Sulfitobacter sp. The 16S rRNA gene sequences of the Pseudoalteromonas isolates are also observed in T-RFLP data and 16S clone libraries for microbial mats at Loihi, indicating that these isolates are environmentally-relevant and abundant in-situ. The ubiquitous distribution of these isolates also suggests that they may play an important role in the submarine alteration of volcanic rocks and the formation of ferromanganese crusts, and thereby affect the net chemical fluxes associated with water-rock exchange.
[Show abstract][Hide abstract] ABSTRACT: Fe, the fourth-most abundant element in the Earth's crust, is also one of the most biologically essential ones. The reduced form, Fe(II), is often considered to be biologically limiting as a result of its low solubility and rapid chemical oxidation to Fe(III)(hydr)oxides at circumneutral pH. The alteration of basaltic glass, enriched in Fe(II), however, provides an abundant supply of reduced iron and, thus, has a major influence on local ocean chemistry and Fe bioavailability. Despite the fact that chemical Fe(II) oxidation takes place very rapidly, we demonstrate that alteration processes of freshly formed basaltic glass can be crucially enhanced by microbial activity.Cultivation of bacteria from basalt surfaces collected from two active submarine volcanoes, Loihi (Hawaii) and Vailulu'u (American Samoa) show a large number of heterotrophic bacteria capable of oxidizing Fe(II) and that these bacteria. not only enhance basalt dissolution but also play a major role in precipitating large amounts of thick Fe(hydr)oxides mats on Vailulu'u Seamount, particularly in the vicinity of low temperature hydrothermal vents. These mats contain substantial quantities of organic carbon that may serve as food sources for some of the macrobiological life on Vailulu'u Seamount. This very prominently includes a substantial population of eels that is found in close spatial association with up to 1m thick Fe oxide/microbial mat at Nafanua volcano, a recent volcanic cone that grew from the crater floor of the seamount. Microbial community analysis on different substrates ranging from basalt surfaces to microbial mats were performed on specially designed culturing media for detection and isolation of heterotrophic bacteria capable of Fe(II)-oxidation. Clone libraries from microbial mats originating from an eel dominated area of Vailulu'u crater are being compared to libraries made from eel guts in order to provide information to what extent these mats are being used as a food source in otherwise nutrient poor and extreme habitats like volcanic seamounts and their hydrothermal systems.
[Show abstract][Hide abstract] ABSTRACT: In recent years there has been as increasing interest in microbe-mineral interactions, specifically the molecular mechanisms of mineral formation and dissolution. While not a true mineral, submarine basaltic glass represents an important rock surface and one of the most reactive components of the ocean crust. The high solubility of reduced glasses and the large disequilibrium with oxygenated seawater leads to large scale chemical exchange of Ca, Mg, Si, Al, Mn, Sr, as well as the pervasive oxidation of Fe(II). A variety of different mechanisms can be envisioned to contribute to the weathering of basalt, yet our basic understanding of what mechanisms actually occur and which are the most important is exceedingly small. To gain a comprehensive understanding of the mechanisms of basalt weathering it is necessary to be able to measure weathering rates, distinguish between biotic and abiotic components of weathering, and relate these rates to the various microbial processes that may be occurring. This requires an integration of geochemical, microbiological, molecular biological and mineralogical approaches. In addition, comparative studies between laboratory and field experiments and between different environments are necessary to assess the dominant pathways for basalt weathering. Given the chemical abundance and availability of reduced Fe and to a lesser extent, reduced Mn in basalts which may serve as energy sources, our group is focusing on bacteria that carry out redox transformations of these metals or produce compounds that complex these metals. Our approach includes cultivation and characterization of bacteria from natural basalt surfaces of various ages and from different environments, and using these isolates for laboratory studies of basalt colonization and weathering. Natural basaltic glass as well as synthetic basaltic substrates amended with enhanced concentrations of Mn, phosphate and varying Fe oxidation states have been placed back in the environment for exposure and retrieval after months to years for subsequent analysis of microbial populations and rates of weathering. Our primary study sites, the seamounts Loihi in Hawai'i and Vailulu'u in American Samoa, provide access to a wide range of environments characterized by different temperatures and chemistry and will allow us to assess the variety mechanisms of basalt weathering and their universality.
[Show abstract][Hide abstract] ABSTRACT: The extreme oligotrophic nature of the oceanic crust was once believed to be an inhospitable environment to support microbial life. However, numerous studies in the past two decades have revealed diverse chemolithotrophic microbial communities inhabiting the deep biosphere within the oceanic crust. Vailulu'u Seamount in American Samoa and Loihi Seamount in Hawai'i provide access to the deep biosphere environments through the study of the interaction of hydrothermal vent water, basaltic substrates and microbial communities. Both seamounts have been found to exhibit similar iron-encrusted microbial mats surrounding both high and low temperature hydrothermal vent orifices. We are targeting iron as the main electron donor/acceptor in these environments due to the relative abundance and availability in basalts. Through the use of the HURL Pisces submersibles, we exposed amended basaltic glasses of several different compositions to a host of different environments on both seamounts in order to study the colonization and biofilm characteristics of the microbial communities. A large culturing effort reveals multiple iron oxidizing and reducing bacteria as members of the microbial community responsible for the colonization and subsequent dissolution and alteration of basaltic glass. We employ an annular reactor to expose the same suite of chemically altered basaltic glasses to a sample of iron microbial mats taken from Vailulu'u to provide a laboratory complement the environmental exposure experiments. Here cell counts reveal a 90% enhanced colonization and growth on the basalt glass versus the surrounding epoxy and borosilicate glass. The ability of microbes to leach nutrients (such as iron) out of the host substrate has far reaching astrobiological implications for nutrient sources available to sustain life in a Mars or Europa biosphere.
[Show abstract][Hide abstract] ABSTRACT: Two miniaturized Mössbauer spectrometers are part of the Athena instrument package of the NASA Mars Exploration Rovers, Spirit
and Opportunity. The primary objectives of their science investigation are to explore two sites on the surface of Mars where
water may once have been present, and to assess past environmental conditions at those sites and their suitability for life.
Aqueous minerals — jarosite at Meridiani Planum, Opportunity’s landing site, and goethite in the Columbia Hills in Gusev Crater,
Spirit’s landing site — were identified by Mössbauer spectroscopy, thus providing in situ proof of water being present at those sites in the past. The formation of jarosite in particular puts strong constraints
on environmental conditions during the time of formation and hence on the evaluation of potential habitability. On Earth Mössbauer
spectroscopy was used to investigate microbially induced changes in Fe oxidation states and mineralogy at the Loihi deep sea
mount, a hydrothermal vent system, which might serve as an analogue for potential habitats in the Martian subsurface and the
sub-ice ocean of Jupiter’s icy moon Europa.