Evidence Of Microbial Activity Research Articles

Evidence of Microbial Activity in Coal Seam Production Water and Hydrochemical Constraints

Evidence of Microbial Activity in Coal Seam Production Water and Hydrochemical Constraints

Multiple sulphur isotope record of Paleoarchean sedimentary rocks across the Onverwacht Group, Barberton Greenstone Belt, South Africa

This study presents multiple sulphur isotope (32 S, 33 S, 34 S, 36 S) data on pyrites from silicified volcano-sedimentary rocks of the Paleoarchean Onverwacht Group of the Barberton greenstone belt, South Africa. These rocks include seafloor cherts and felsic conglomerates that were deposited in shallow marine environments preserving a record of atmospheric and biogeochemical conditions on the early Earth. A strong variation in mass independent sulphur isotope fractionation (MIF-S) anomalies is found in the cherts, with Δ33 S ranging between -0.26‰ and 3.42‰. We explore possible depositional and preservational factors that could explain some of this variation seen in MIF-S. Evidence for microbial activity is recorded by the c. 3.45 Ga Hooggenoeg Formation Chert (HC4) preserving a contribution of microbial sulphate reduction (-Δ33 S and -δ34 S), and a c. 3.33 Ga Kromberg Formation Chert (KC5) recording a possible contribution of microbial elemental sulphur disproportionation (+Δ33 S and -δ34 S). Pyrites from a rhyo-dacitic conglomerate of the Noisy Formation do not plot along a previously proposed global Felsic Volcanic Array, and this excludes short-lived pulses of intense felsic volcanic gas emissions as the dominant control on Archean MIF-S. Rather, we suggest that the MIF-S signals measured reflect dilution during marine deposition, early diagenetic modification, and mixing with volcanic/hydrothermal S sources. Given the expanded stratigraphic interval (3.47-3.22 Ga) now sampled from across the Barberton Supergroup, we conclude that large MIF-S exceeding >4‰ is atypical of Paleoarchean near-surface environments on the Kaapvaal Craton.

Evidence of microbial activity in a uranium roll-front deposit: Unlocking their potential role as bioenhancers of the ore genesis

Uranium (U) roll-front deposits constitute a valuable source for an economical extraction by in situ recovery (ISR) mining. Such technology may induce changes in the subsurface microbiota, raising questions about the way their activities could build a functional ecosystem in such extreme environments (i.e.: oligotrophy and high SO4 concentration and salinity). Additionally, more information is needed to dissipate the doubts about the microbial role in the genesis of such U orebodies. A U roll-front deposit hosted in an aquifer driven system (in Zoovch Ovoo, Mongolia), intended for mining by acid ISR, was previously explored and showed to be governed by a complex bacterial diversity, linked to the redox zonation and the geochemical conditions. Here for the first time, transcriptional activities of microorganisms living in such U ore deposits are determined and their metabolic capabilities allocated in the three redox-inherited compartments, naturally defined by the roll-front system. Several genes encoding for crucial metabolic pathways demonstrated a strong biological role controlling the subsurface cycling of many elements including nitrate, sulfate, metals and radionuclides (e.g.: uranium), through oxidation-reduction reactions. Interestingly, the discovered transcriptional behaviour gives important insights into the good microbial adaptation to the geochemical conditions and their active contribution to the stabilization of the U ore deposits. Overall, evidences on the importance of these microbial metabolic activities in the aquifer system are discussed that may clarify the doubts on the microbial role in the genesis of low-temperature U roll-front deposits, along the Zoovch Ovoo mine.

Holocene Lacustrine Abiotic Aragonitic Ooids from the Western Qaidam Basin, Qinghai-Tibetan Plateau

Carbonate ooids are a significant component of shallow water carbonate deposits in the present and geologic past, yet their origin and formation mechanism have been the subject of continuing debate. This study focuses on the well-preserved Holocene aragonitic ooids collected from the west Qaidam Basin, Qinghai-Tibetan Plateau (QTP). The mineralogical and chemical compositions, and stable (δ13C and δ18O), and radiocarbon isotopes of the ooids were analyzed to investigate their formation and develop a depositional model. The ooids formed approximately 5377±61 cal BP, and their cortices were composed of microcrystalline aragonite, with most nuclei being quartz grains. Stable carbon and oxygen isotopes indicate that authigenic aragonite precipitation is driven by evaporation and associated degassing of CO2 under turbulence conditions in a shallow alkaline lakes. Furthermore, eletron microscopy showed no presence of microfossils in ooid cortices or other evidence of microbial activity. Therefore, we propose that aragonite precipitation during ooid formation is most likely induced abiotically by increasing alkalinity due to evapoconcentration of lake waters based on an absence of an efficient carbonate-inducing metabolic pathway. New observations and detailed analyses of aragonitic ooid samples in the Qaidam Basin provide an improved understanding of the origin and formation processes of carbonate ooid in modern environment and the geologic past.

Dissolved Nitrogen Speciation and Concentration During Spring Thaw in the Greenland Ice Sheet Dark Zone: Evidence for Microbial Activity

This study provides the first contemporaneous measurements of the concentration and speciation of dissolved nitrogen (N) in snow, meltwater and ice during the onset of the ablation season at a site within the Dark Zone of the Greenland Ice Sheet. The decaying, partially leached snow pack near S6 in south-west Greenland produced meltwater with relatively constant nitrate (NO3−) concentrations, approximating the snow pack average (1.1 µM). By contrast, ammonium (NH4+) (0–∼ 4 µM) and dissolved organic nitrogen (DON) (0–∼ 3 µM) concentrations were more variable, and sometimes higher than the average snow pack concentrations of 1.0 and 0.4 µM, respectively. This variability could be the result of microbial uptake and production within the melting snow pack. We observed pooled meltwater at the snow-ice interface that appeared to scavenge DON (∼1–8 µM) and possibly NO3− (∼1–2 µM) from the underlying ice, whose initial surface was a continuum of superimposed ice and weathering crust from the previous season. The shallow meteoric ice (∼10 cm–1 m) beneath the snow pack had high concentrations of DON and NH4+(6.5 and 2.6 µM, respectively), while NO3− concentrations were similar to the snow pack (1.1 µM). The absence of NH4+ in the snowmelt traversing the snow-ice interface may also point to microbial activity occurring at this boundary layer. Melt modelling indicated the presence of liquid meltwater at the snow-ice interface and that at least 10 cm of the surface ice below the snow pack was at 0°C. Solar radiation transmitted through the thin snow pack to the ice surface is absorbed by pigmented glacier algae causing melt of the surrounding ice, allowing the possibly of photosynthesis to begin under the thinning snowpack in these micro-melt environments. Hence, we conjecture that glacier algal blooms can commence before the snow pack has completely melted, occuring at a time when meltwaters are enhanced in nutrients scavenged from the snowpack, superimposed ice and the remnants of the weathering crust from the previous year.

Mineral authigenesis within chemosynthetic microbial mats: Coated grain formation and phosphogenesis at a Cretaceous hydrocarbon seep, New Zealand

AbstractMarine hydrocarbon seeps are sites of chemosynthetic microbial activity and authigenic carbonate formation. Seep limestones are typified by a range of geochemical signatures of microbial hydrocarbon oxidation, but only few seep deposits reveal mesofabrics that can be regarded as evidence of microbial activity. A Cretaceous methane‐seep limestone from Waipiro Bay, New Zealand, exhibits a fabric composed of cryptocrystalline carbonate fluorapatite between carbonate coated grains and spheroidal calcite. To understand the unusual Waipiro deposit, a paragenetic sequence has been derived for coated grains, spheroidal calcite and carbonate fluorapatite using thin section petrography, scanning electron microscopy, Fourier‐transform infrared spectroscopy and stable isotope geochemistry. The formation of 13C‐depleted coated grains (δ13C values as low as −15.8‰ Vienna‐Pee Dee Belemnite) and spheroidal calcite (δ13C values as low as −21.3‰) was favoured by hydrocarbon oxidation. Fibrous banded and botryoidal cement, a typical early diagenetic phase of hydrocarbon‐seep deposits, features δ13C values as low as −22.9‰. Coated grains and spheroidal calcite grew by displacive growth in a gel‐like medium, probably a microbial mat. Phosphorus is a mobile element and marine pore waters are typically undersaturated with respect to carbonate fluorapatite. Specific conditions are consequently required to retain sufficient concentrations to precipitate carbonate fluorapatite. Possible sources of phosphorus for the formation of the 13C‐depleted Waipiro carbonate fluorapatite (mean δ13C value of −15.4‰) include (a) the oxidation of sedimentary organic matter by organoclastic sulphate reduction, (b) the degradation of the microbial mat itself and (c) the active release of polyphosphate by sulphide‐oxidizing bacteria. This study suggests that the formation of the Cretaceous Waipiro seep limestone involved an interplay of biogeochemical processes including sulphate‐driven anaerobic oxidation of methane, organoclastic sulphate reduction and possibly nitrate‐dependent sulphide oxidation. It further demonstrates that coated grains resembling oncoids are not restricted to shallow water, photosynthesis‐dependent ecosystems.

Micromorphological and chemical investigation of late-Viking age grave fills at Hofstaðir, Iceland

Grave fills from seven human burials from a late-Viking age - early medieval cemetery at Hofstaðir, Mývatnssveit (Iceland) were examined by soil micromorphology and organic chemical analysis. Detailed analysis of the weathering of the mineral constituents of the grave fills demonstrates a relationship between the extent of weathering of volcanic silicates within the fills and the presence of buried human remains. Gas chromatography-mass spectrometry (GC–MS) of extracts from the fills and controls of two graves revealed organic signatures dominated by plant-derived organic matter, with no evidence of degradation products of the body tissues. Transformation of n-alkanes into n-alkan-2-ones provides evidence for microbial activity within the fills. GC–MS analysis of the organic extract from under one of the skulls and pyrolysis gas chromatography of wood fragments found in that grave provide compelling evidence for the former presence of a conifer wood coffin. The use of this non-native wood in the burial provides evidence for either the import of foreign lumber or the utilisation of driftwood, most likely originating from Russia/Siberia.

Development of a cell immobilization technique with polyvinyl alcohol for diesel remediation in seawater

The objective is to develop and evaluate a PVA cell immobilization technology in degrading diesel in seawater. The inclusion of activated carbons improved the TPHd degradation efficiency up to 47%. The optimal combination of the immobilized cells, Design H (dominant Rhodococcus pyridinivorans CC-HCCH11), achieved relatively high TPHd degradation efficiency of 92%, and reduced TPHd from 2168.65 ± 74.52 to 164.42 ± 3.26 mg L−1. Design J (dominant Gordonia alkanivorans CC-JG39) achieved the highest degradation rate k (0.0041 hr−1) with the final degradation efficiency of 88%. The chromatograph explained the superiority of Design H and J. The plate counts revealed a consistent degradation pattern with the genomic DNA’s, with correlation coefficient ranging from 0.774 to 0.915. The water quality analysis indicated adequate consumptions and evidence of microbial activity. The developed PVA immobilization technique is helpful in solving the potential environmental problem by using it as resources for environmental remediation. Design H is a recommended bacterial cell combination.

Microstructural characterization of carbon steel corrosion in clay borehole water under anoxic and transient acidic conditions

The corrosion interface of low-alloy carbon steel (C-steel) coupons (P235, ferrite-pearlitic with a columnar microstructure) reacted in clay porewater seeping in a test chamber in situ in the Callovo-Oxfordian formation of the Meuse-Haute Marne Underground laboratory (France) was probed by microscopic and microspectrocopic techniques. Two series of samples were investigated, with extensive and limited corrosion, respectively. For extensively corroded coupons, several layers of inner corrosion products were observed. The innermost layer was made of Cl-rich Fe (hydr)oxide, later evolving to form a massive β-Fe2(OH)3Cl unit close to C-steel, and sometimes crossed by magnetite ribbons sticking to cementite lamellas, or by patches of green rust. The second inner layer was made of veinlets of Fe hydrated silicate with a sponge-like morphology, a molecular-scale structure reminiscent of clay minerals, and containing nodules of siderite and chukanovite. These (hydroxy)carbonate solids sometimes merged to form a massive layer close to the trace of the original surface. The layers external to this original surface were discontinuous and made of successively Ca-doped siderite (ankerite), Fe sulfide, S‐rich Fe silicate, and finally pyrite nodules and ankerite. For the samples with limited damage, no β-Fe2(OH)3Cl layer was observed, siderite or chukanovite were in close contact with metal, sometimes with interfacial magnetite, and the veinlets of Fe hydrated silicate were less developed. Only external layers of Fe sulfide and ankerite were observed. This suggests that these slightly corroding samples were in fact confined. Evidence for microbial activity was obtained in the form of a Fe sulfide fringe mixed with ankerite. Microbial activity may have induced some local heterogeneity in corrosion processes, e.g. by changing local pH conditions at mm-scale.

Sulfur and carbon geochemistry of the Santa Elena peridotites: Comparing oceanic and continental processes during peridotite alteration

Ultramafic rocks exposed on the continent serve as a window into oceanic and continental processes of water–peridotite interaction, so called serpentinization. In both environments there are active carbon and sulfur cycles that contain abiogenic and biogenic processes, which are eventually imprinted in the geochemical signatures of the basement rocks and the calcite and magnesite deposits associated with fluids that issue from these systems. Here, we present the carbon and sulfur geochemistry of ultramafic rocks and carbonate deposits from the Santa Elena ophiolite in Costa Rica. The aim of this study is to leverage the geochemistry of the ultramafic sequence and associated deposits to distinguish between processes that were dominant during ocean floor alteration and those dominant during low-temperature, continental water–peridotite interaction.The peridotites are variably serpentinized with total sulfur concentrations up to 877ppm that is typically dominated by sulfide over sulfate. With the exception of one sample the ultramafic rocks are characterized by positive δ34Ssulfide (up to +23.1‰) and δ34Ssulfate values (up to +35.0‰). Carbon contents in the peridotites are low and are isotopically distinct from typical oceanic serpentinites. In particular, δ13C of the inorganic carbon suggests that the carbon is not derived from seawater, but rather the product of the interaction of meteoric water with the ultramafic rocks. In contrast, the sulfur isotope data from sulfide minerals in the peridotites preserve evidence for interaction with a hydrothermal fluid. Specifically, they indicate closed system abiogenic sulfate reduction suggesting that oceanic serpentinization occurred with limited input of seawater. Overall, the geochemical signatures preserve evidence for both oceanic and continental water–rock interaction with the majority of carbon (and possibly sulfate) being incorporated during continental water–rock interaction. Furthermore, there is evidence for microbial activity that was possibly stimulated by carbon sourced from water–rock interaction with adjacent sediments or fluid inclusions. This study provides detailed insight into the complex hydrothermal history of continental serpentinization systems and adds to our understanding of the carbon and sulfur cycling within peridotite-hosted hydrothermal systems.

Enigmatic spheres from the Upper Triassic Lockatong Formation, Newark Basin of eastern Pennsylvania: evidence for microbial activity in marginal-lacustrine strandline deposits

Microbes within sediments often create films or thick mats that interact with mobile sediment, producing microbially induced sedimentary structures (MISS). Preserved microbes in these sedimentary features are difficult to find, especially in oxygen-rich environments. The study of recent discoveries in the Upper Triassic Norian Lockatong Formation, a dominantly lacustrine facies of the Newark Supergroup strata, has revealed rarely reported structures that are assignable as MISS, namely, sand-cored spheres encapsulated in thin mudstone which range in diameter from the sub-millimetre to millimetre scale. These spheres are embedded in a thin layer of very fine silt and mudstone developed in an interpreted marginal-lacustrine shoreline setting. The cores of the spheres consist of randomly oriented, graded, fine-grained sandstone to siltstone; this eliminates previously proposed physical and biological origins for spheres, leaving a microbial origin. The microbial bound sand balls are localised and generated from a graded bed bound by microbial mats both above and below. The bounded bed was eroded and shaped into spheres during transport. The mats added cohesion by providing extrapolymeric substances which prevented the breakdown of the spheres into individual grains. The mats were rolled into spheres during transportation, thus preserving the microbial bound core. These sand balls add to the catalog of microbial diversity that can be used to increase our understanding of biological systems in lacustrine settings.

The diversification of modern animals: Douglas Erwin and James Valentine on the Cambrian explosion

Book details The Cambrian Explosion: The Construction of Animal Biodiversity, by Douglas H. Erwin and James W. Valentine. Greenwood Village, CO: Roberts & Co. 2013. Pp ix + 406. H/b $60.00, ISBN 978-1-936211-03-5. When writing The Origin of Species, Darwin (1859, pp. 306-309) puzzled over the abrupt beginning of life’s fossil record: after long, seemingly lifeless eras, an extraordinary diversity of marine life suddenly burst forth into the geological record. Nowadays, the trained minds of geologists and microbial biochemists see abundant evidence of microbial activity in these seemingly lifeless pre-Cambrian rocks: indeed, these microbes’ photosynthesis and chemosynthesis transformed the chemistry of the oceans and the geology of their sediments (Fischer 1984, Konhauser 2007). Since Darwin’s time, a pre-Cambrian biota of macroscopic multicellular organisms, the Ediacaran biota, has been discovered, although just what these organisms were, or even whether they were all aquatic, is far from settled (Knauth 2013, Retallack 2013, Xiao 2013). It remains true that the first organisms we can recognize as members of living phyla burst into the fossil record, in remarkable diversity, with disconcerting suddenness, in the Cambrian period, beginning 540 million years ago. What happened? In The Cambrian Explosion, two paleontologists, Douglas Erwin and his former dissertation advisor James Valentine, document the explosion of diversity in the Cambrian, and the events leading up to it, in lavishly illustrated detail. This story begins with the origin about two billion years ago — by an Archaean incorporating bacterial symbionts capable of aerobic respiration — of

Evidence for microbial activity in British and Irish Ordovician pillow lavas

Pyrite is consistently found in modern seafloor vesicular basalts and has a sulphur isotopic composition consistent with microbial activity. We present S isotope data from pyrite in Ordovician pillow lavas at localities across the British Isles, which yield a range of δ34S compositions consistent with two components of sulphur: groundmass pyrite (~0 ± 4‰) and 32S‐enriched pyrite in the vesicles (−8‰ to −27‰). The latter are recorded from vesicular lavas in four different terranes, representing different settings at the margins of the Iapetus Ocean. Whereas a component of magmatic sulphate is recognized in the groundmass values, the isotopically light data in the vesicles are consistent with microbial reduction of seawater sulphate in sub‐seafloor lavas. This is consistent with modern examples and indicates considerable longevity for this sub‐seafloor microbial habitat. Copyright © 2014 John Wiley & Sons, Ltd.

Geophysical Signatures of Subsurface Microbial Processes

Microbes are found in almost every conceivable part of the Earth, from hydrothermal vents in the deep ocean basins [Huber et al., 2007] to the cold subglacial lakes of Antarctic ice sheets [Mikucki et al., 2009]. The role of microorganisms in transforming Earth systems (e.g., accelerating mineral weathering) by mediating different biogeochemical cycles over the past 4 billion years has been well documented in many studies [e.g., Banfield et al., 1999]. However, microbial processes are challenging to investigate in situ. Direct (e.g., microbial composition and population density) and indirect (e.g., alteration of mineral phases by microbial activity) evidence for microbial activity requires sampling from boreholes, which is costly and invasive and provides poor spatial coverage.

Insights into Cave Architecture and the Role of Bacterial Biofilm

Caves offer a stable and protected environment from harsh and changing outside conditions. They lend living proof of the presence of minute life forms that delve deep within the earth’s crust where the possibility of life seems impossible. Devoid of all light sources and lacking the most common source of energy supplied through photosynthesis, the mysterious microbial kingdom in caves are consequently dependent upon alternative sources of energy derived from the surrounding atmosphere, minerals and rocks. There are a number of features that can be observed within a cave that may serve as evidence of microbial activity, for example, formation of biofilms comprised of multiple layers of microbial communities held together by protective gel-like polymers which form complex structures. Different bacterial biofilms can develop on the walls of the cave which can be visually distinguished by their colorations. Moreover, the pH generated by the metabolism of bacterial biofilm on the cave environment can lead to precipitation or dissolution of minerals in caves. Caves also offer an excellent scenario for studying biomineralization processes. The findings on the association of bacteria with secondary minerals as mentioned in this review will help to expand the existing knowledge in geomicrobiology and specifically on the influence of microorganisms in the formation of cave deposits. This paper reviews the current state of knowledge of biospeleology of caves and the associated bacterial biofilms. Recommendations for future research are mentioned to encourage a drift from qualitative studies to more experimental studies.

Lacustrine carbonates in rift settings: the interaction of volcanic and microbial processes on carbonate deposition

Abstract The relatively simplistic facies models for lacustrine carbonates do not currently incorporate either the diversity of microbialite carbonate development or the influence of volcanic-related processes found in rift settings. The basic nature of the carbonate factories in these systems, whether microbial, macrophytic, skeletal or abiogenic, is not resolved. Lacustrine microbialites can develop in shallow lakes as concentrations of microbialite mounds covering many hundreds of square kilometres, or as bathymetrically controlled facies belts, but in many rift settings vent-related thermal and non-thermal carbonates (travertines and tufas) are a major component. Subaqueous vent-related carbonates, with evidence of microbial activity, can produce seismic-scale carbonate build-ups in deeper lakes or apparently more stratiform accumulations in shallow lakes. In lakes with only volcanic catchments, Mg and silica activity, coupled with high carbonate alkalinity and microbial influences, can potentially generate a complex set of mineral–microbe interactions and products, creating a unique set of challenges for predicting and understanding reservoirs in such settings.

Fossil evidence for micro- and macrofaunal utilization of large nekton-falls: Examples from early Cenozoic deep-water sediments in Washington State, USA

Whale and fish carcasses and wood in the deep-sea host diverse and specialized faunas related to the hydrothermal vent and hydrocarbon seep biota. Fossil examples of such food-falls were found in the Eocene to Oligocene Crescent, Humptulips, Lincoln Creek, and Pysht formations in western Washington State, USA. They are used to document paleoecologic and taphonomic features of such sites. Paleontological evidence for ecologic processes occurring at ancient whale falls include: shark teeth indicating the presence of scavengers; bored bone surfaces showing microbial bone degradation; and bivalves belonging to chemosymbiotic groups. The latter indicator shows that sulfide was released from the anaerobic decay of carrion and/or bone lipids. It appears that the type of taxa and the low number of specimens mark a ‘chemotrophic opportunist stage’ that lasted only a few years. Furthermore, detritus in the marrow spaces of cancellous bones indicate that the bones were hollow for a significant length of time before burial, perhaps 1000 years or more. These spaces are now mostly filled with clotted micrite and other cement phases, the δ 13C values of which are in the same range as those of the concretionary matrix enclosing the bones, indicating cement formation within the sediments. A piece of wood from the Pysht Formation shows evidence for two generations of wood-boring bivalves, such that some boreholes have calcitic linings characteristic for teredinids, and some are lined with a crust of decomposed wood characteristic for xylophagains. Several investigated fossil wood-falls show that wood-boring bivalves were active on the seafloor: fecal pellets composed of woody detritus are abundant in the concretionary matrix surrounding the wood. The excellent preservation of these fecal pellets indicates that these concretions with wood and associated mollusks represent undisturbed, in situ wood-fall communities. In sum, undisturbed deep-water sediments can preserve evidence of life and ecologic processes at short-lived nekton-falls. However, the data also indicate a long time interval between the macrofaunal utilization of the substrates, and the cementation and fossilization of these associations. Thus using mineral deposits such as clotted micrite and pyrite as evidence for microbial activity during the macrofaunal utilization of the substrates is doubtful.

Evidence of microbial activity in siderite and calcite deposits on gastropod shells in Pliocene sand and clay beds from Lipovljani, Croatia

Freshwater Pliocene sand and clays found near Lipovljani in western Slavonia, Croatia, contain gastropods preserved by diagenetic mineral incrustations of alternating calcite and siderite. The geochemical possibility of siderite formation is evaluated, and evidence for microbial mediation of siderite deposition around fossil carbonate shells is presented.

Possible evidence for panspermia: the labelled release experiment

Abstract30 years after the Viking Mission landed on Mars (20 July 1976) to search for life, despite the positive findings of the Labelled Release (LR) experiment, the issue remains unresolved. The controversial history, following the immediate dismissal of the LR’s evidence for microbial activity in the Martian soil, and the later claim to its having found living microorganisms are reviewed. The bearing of post-Viking-to-current data on the issue is discussed in the context of the scientific community’s growing interest in the long-dismissed possibility of microbial life on Mars. Objections raised over the years to the biological interpretation of the Mars LR, those currently maintained, and their rebuttals are reviewed. A case is presented that enough evidence now exists for an objective review by astrobiologists to resolve this key issue, a review, surprisingly, not yet held. The results could greatly influence NASA’s currently shifting plans for Mars exploration. A variation of the LR experiment to test for chiral specificity in the metabolism of substrates by the active agent found in the Martian soil, and thus having the capability of obtaining an unambiguous answer to the life question, is proposed. Confirmation of life on Mars by this experiment can also determine whether Martian and Earth life forms share a common heritage. Together with mounting evidence for the viable transfer of microorganisms between the two planets, this would be evidence for panspermia, and establish the presence of a common biosphere in which the two planets participate. Should Martian microorganisms show a different chiral specificity than that of Earth life then this would indicate separate origins of the two neighbouring life forms, thereby strongly implying that life occurs widely throughout the cosmos. Any one of these possible outcomes would be a paradigm-breaking event.

Intrinsic bioremediation of diesel-contaminated cold groundwater in bedrock

In 1982 diesel fuel migrated from a well lease site into underlying fractured bedrock contaminating the groundwater-bearing zone approximately 30 m below ground surface. Historical contaminant concentrations, geochemical indicators, and microbiological data were analysed to evaluate natural attenuation, specifically intrinsic bioremediation. Evidence of microbial activity was provided by most probable number (MPN) and commercial biological activity reaction tests (BART™). Laboratory microcosms using groundwater from the site were incubated under aerobic and anaerobic conditions with electron acceptor and nutrient amendment to assess microbial activity. Aerobic biodegradation rates were determined by measuring mineralization of 14C-dodecane. Nutrient amendment combined with a higher temperature (28 °C) increased the first-order aerobic biodegradation rate to 0.0066 d–1 from 0.0002 d–1 at 10 °C. Anaerobic biodegradation rates were calculated from depletion of total extractable hydrocarbons (TEH) over 717 d at 10 °C. Nutrient addition increased the anaerobic first-order biodegradation rate to 0.0016 from 0.0005 d–1. Data from these laboratory microcosms indicate that the current slow rates of intrinsic bioremediation may be enhanced with nutrient addition. Key words: intrinsic bioremediation, natural attenuation, groundwater, diesel fuel, hydrocarbon biodegradation, anaerobic hydrocarbon biodegradation, biological activity reaction test (BART™).