Psychrophiles are presumed to play a large role in the catabolism of alkanes and other components... more Psychrophiles are presumed to play a large role in the catabolism of alkanes and other components of crude oil in natural low temperature environments. In this study we analyzed the functional diversity of genes for alkane hydroxylases, the enzymes responsible for converting alkanes to more labile alcohols, as found in the genomes of nineteen psychrophiles for which alkane degradation has not been reported. To identify possible mechanisms of low temperature optimization we compared putative alkane hydroxylases from these psychrophiles with homologues from nineteen taxonomically related mesophilic strains. Seven of the analyzed psychrophile genomes contained a total of 27 candidate alkane hydroxylase genes, only two of which are currently annotated as alkane hydroxylase. These candidates were mostly related to the AlkB and cytochrome p450 alkane hydroxylases, but several homologues of the LadA and AlmA enzymes, significant for their ability to degrade long-chain alkanes, were also de...
We isolated 16 antibiotic-producing bacterial strains throughout the central Arctic Ocean, includ... more We isolated 16 antibiotic-producing bacterial strains throughout the central Arctic Ocean, including seven Arthrobacter spp. with almost identical 16S rRNA gene sequences. These strains were numerically rare, as revealed using 454 pyrosequencing libraries. Arthrobacter spp. produced arthrobacilins A to C under different culture conditions, but other, unidentified compounds likely contributed to their antibiotic activity.
ABSTRACT A novel method (SCIFAR) is described for measuring microbial respiration for organisms g... more ABSTRACT A novel method (SCIFAR) is described for measuring microbial respiration for organisms grown on an isotopically light substrate. Applied to cultures of Colwellia psychrerythraea at very low temperatures a new record for low temperature activity was set for this organism.
ABSTRACT The science surrounding missions to the outer planets has been dominated by geophysical ... more ABSTRACT The science surrounding missions to the outer planets has been dominated by geophysical questions. The Europa Jupiter System Mission (EJSM), however, is a search explicitly for a ``habitable world''. While not a life detection mission, the presence of ice penetrating radar (IPR) and other instruments provides an opportunity to answer questions that are biological in nature. The IPR will characterize the ice structure, including any subsurface water and ice-water interfaces. If life is to be found on Europa it may be present at the first water-ice interface; water lenses within the shell closer to the Europan surface than the ice-ocean interface. IPR can confirm the presence and abundance of these putative habitats, potentially within range of future life detection missions. EJSM will also directly inform biologists by determining some ice properties and estimating its rate of overturn, constraining the flux of oxidants and thus the amount of metabolism that can be supported. Terrestrial analogues may be useful models for the Europan ice-ocean system as revealed by IPR. The underside of sea ice represents a concentrated zone of life, defined by the availability of energy, along a column thousands of meters in length. For phototrophs attachment to the underside of sea ice guarantees access to light. For heterotrophs association ensures a supply of chemical energy in the form of organic carbon. If life exists on Europa we might expect a similar scenario, in this case with chemolithotrophs using the ice as a conduit for energy. This strategy suggests that if life is to be found on Europa it may well reach its highest concentration at the uppermost ice-water interface. Similarly, within saline ice biology is strongly associated with interstitial spaces: microscale channels and pores that result from the differential freezing of saline water. Within these spaces material is concentrated, providing an environment enriched in chemical energy. Here we present several habitat parameters that can be directly assessed via IPR, and discuss biological questions that EJSM may answer in the context of terrestrial analogues with an emphasis on multiyear sea ice (MYI). Although subglacial lakes may be analogues for a biosphere deep in the Europan ocean, MYI may share more structural similarities with the Europan ice shell than grounded glacial ice. Calculations suggest that organic and inorganic materials within the interstial spaces of MYI are concentrated as much as 500 fold, possibly aiding microbial metabolism through periods of very low temperature. In a similar manner organic carbon from endogenic or exogenic sources on Europa would concentrate in these spaces, serving as a valuable electron donor or acceptor for organisms in the ice. An environment's physical structure helps structure the community which inhabits it, thus the MYI microbial community should inform a developing model of a hypothetical Europan ecosystem. Recent applications of 454 sequencing technology to the MYI community indicates a surprising degree of diversity within this environment, similar to that of underlying seawater. These findings suggest the potential for a diverse Europan microbial ecosystem despite energy limitations imposed by a permanent ice cover.
ABSTRACT The science surrounding missions to the outer planets has been dominated by geophysics. ... more ABSTRACT The science surrounding missions to the outer planets has been dominated by geophysics. However, a mission to Europa, the top mission priority from the last decade and a uniquely compelling mission for flight in this decade, represents a search explicitly for a "habitable world." A comprehensive dialogue about life in the ice is critical since habitability is not singularly defined by shell thickness or the existence of water. Here, we present evidence from the Earth's cryosphere for life adapted to ice and how habitability can be remotely quantified, discuss implications for the ice shell, and demonstrate how radar sounding opens the door for answering the question: can life exist in Europa's ice?
On the hemispheric scale, snow on the surface of sea ice significantly impacts the exchange of ma... more On the hemispheric scale, snow on the surface of sea ice significantly impacts the exchange of mass and energy across the ocean-ice-atmosphere interface. The snow cover over Arctic sea ice plays a central role in Arctic photochemistry, including atmospheric depletion events at the onset of spring, and in ecosystem support, by determining the availability of photosynthetically active radiation for algal primary production at the bottom of the ice. Among the non-uniformities of snow relevant to its larger-scale roles is salt content. When snow is deposited on the surface of new sea ice, brine expelled onto the ice surface during ice formation wicks into the snow by capillary action, forming a brine-wetted or saline snow layer at the ice-snow interface. A typical salinity for this basal snow layer in the Arctic (measured on a 3-cm depth interval of melted snow) is about 20 (ppt by optical salinometer), with maxima approaching 30 ppt, thus higher than the salinity of melted surface sea ice (< 12 ppt). Although the physical-chemical properties of this brine-wetted layer have been examined in recent years, and the (assumed) air-derived microbial content of overlying low-salinity snow is known to be low in winter, basal saline snow is essentially unexplored as a microbial habitat. As part of an NSF-supported project on frost flowers, we investigated snow overlying coastal sea ice off Barrow, Alaska, in February 2010 (since snow buries frost flowers). Sterile (ethanol-rinsed) tools were used to open snow pits 60 cm wide, record temperature by thermoprobe at 3-cm depth intervals, and collect samples from newly exposed snow walls for salinity (3-cm intervals) and biological measurements (6-cm intervals). The latter included counts of bacterial abundance by epifluorescence microscopy and assays of extracellular polysaccharide substances (EPS). We also sampled snow on a larger scale to extract sufficient DNA to analyze microbial community composition (ongoing work), as well as underlying sea ice for comparative purposes. Results indicated presence of an areally extensive saline snow layer (salinities of 18.5-30.9 ppt) that was enriched in bacteria (0.28-1.5 x 10E4 bacteria/ml) and EPS (0.07-0.22 mg glucose equivalents/L) relative to overlying low-salinity snow (0.3-9 ppt; 2-9 x 10E2 bacteria/ml; 0.021-0.11 mg glucose equivalents/L). Analysis of content and distribution of salts, bacteria and EPS throughout the snow and underlying sea ice indicated sea-ice brines as the source of these materials in snow. Although marine bacteria appeared to have moved upwards into snow in sync with brine, EPS was subject to different transport or production and degradation pathways, perhaps connected to a detected sensitivity of bacteria in upper sea ice brines to osmotic shock. The possible passive and dynamic roles of bacteria and their exudates in these brine-wetted snows in influencing the physical-chemical properties of snow over sea ice, including later season physical and biological impacts as the snow melts and infiltrates the ice below, await further study.
Psychrophiles are presumed to play a large role in the catabolism of alkanes and other components... more Psychrophiles are presumed to play a large role in the catabolism of alkanes and other components of crude oil in natural low temperature environments. In this study we analyzed the functional diversity of genes for alkane hydroxylases, the enzymes responsible for converting alkanes to more labile alcohols, as found in the genomes of nineteen psychrophiles for which alkane degradation has not been reported. To identify possible mechanisms of low temperature optimization we compared putative alkane hydroxylases from these psychrophiles with homologues from nineteen taxonomically related mesophilic strains. Seven of the analyzed psychrophile genomes contained a total of 27 candidate alkane hydroxylase genes, only two of which are currently annotated as alkane hydroxylase. These candidates were mostly related to the AlkB and cytochrome p450 alkane hydroxylases, but several homologues of the LadA and AlmA enzymes, significant for their ability to degrade long-chain alkanes, were also de...
We isolated 16 antibiotic-producing bacterial strains throughout the central Arctic Ocean, includ... more We isolated 16 antibiotic-producing bacterial strains throughout the central Arctic Ocean, including seven Arthrobacter spp. with almost identical 16S rRNA gene sequences. These strains were numerically rare, as revealed using 454 pyrosequencing libraries. Arthrobacter spp. produced arthrobacilins A to C under different culture conditions, but other, unidentified compounds likely contributed to their antibiotic activity.
ABSTRACT A novel method (SCIFAR) is described for measuring microbial respiration for organisms g... more ABSTRACT A novel method (SCIFAR) is described for measuring microbial respiration for organisms grown on an isotopically light substrate. Applied to cultures of Colwellia psychrerythraea at very low temperatures a new record for low temperature activity was set for this organism.
ABSTRACT The science surrounding missions to the outer planets has been dominated by geophysical ... more ABSTRACT The science surrounding missions to the outer planets has been dominated by geophysical questions. The Europa Jupiter System Mission (EJSM), however, is a search explicitly for a ``habitable world&#39;&#39;. While not a life detection mission, the presence of ice penetrating radar (IPR) and other instruments provides an opportunity to answer questions that are biological in nature. The IPR will characterize the ice structure, including any subsurface water and ice-water interfaces. If life is to be found on Europa it may be present at the first water-ice interface; water lenses within the shell closer to the Europan surface than the ice-ocean interface. IPR can confirm the presence and abundance of these putative habitats, potentially within range of future life detection missions. EJSM will also directly inform biologists by determining some ice properties and estimating its rate of overturn, constraining the flux of oxidants and thus the amount of metabolism that can be supported. Terrestrial analogues may be useful models for the Europan ice-ocean system as revealed by IPR. The underside of sea ice represents a concentrated zone of life, defined by the availability of energy, along a column thousands of meters in length. For phototrophs attachment to the underside of sea ice guarantees access to light. For heterotrophs association ensures a supply of chemical energy in the form of organic carbon. If life exists on Europa we might expect a similar scenario, in this case with chemolithotrophs using the ice as a conduit for energy. This strategy suggests that if life is to be found on Europa it may well reach its highest concentration at the uppermost ice-water interface. Similarly, within saline ice biology is strongly associated with interstitial spaces: microscale channels and pores that result from the differential freezing of saline water. Within these spaces material is concentrated, providing an environment enriched in chemical energy. Here we present several habitat parameters that can be directly assessed via IPR, and discuss biological questions that EJSM may answer in the context of terrestrial analogues with an emphasis on multiyear sea ice (MYI). Although subglacial lakes may be analogues for a biosphere deep in the Europan ocean, MYI may share more structural similarities with the Europan ice shell than grounded glacial ice. Calculations suggest that organic and inorganic materials within the interstial spaces of MYI are concentrated as much as 500 fold, possibly aiding microbial metabolism through periods of very low temperature. In a similar manner organic carbon from endogenic or exogenic sources on Europa would concentrate in these spaces, serving as a valuable electron donor or acceptor for organisms in the ice. An environment&#39;s physical structure helps structure the community which inhabits it, thus the MYI microbial community should inform a developing model of a hypothetical Europan ecosystem. Recent applications of 454 sequencing technology to the MYI community indicates a surprising degree of diversity within this environment, similar to that of underlying seawater. These findings suggest the potential for a diverse Europan microbial ecosystem despite energy limitations imposed by a permanent ice cover.
ABSTRACT The science surrounding missions to the outer planets has been dominated by geophysics. ... more ABSTRACT The science surrounding missions to the outer planets has been dominated by geophysics. However, a mission to Europa, the top mission priority from the last decade and a uniquely compelling mission for flight in this decade, represents a search explicitly for a &quot;habitable world.&quot; A comprehensive dialogue about life in the ice is critical since habitability is not singularly defined by shell thickness or the existence of water. Here, we present evidence from the Earth&#39;s cryosphere for life adapted to ice and how habitability can be remotely quantified, discuss implications for the ice shell, and demonstrate how radar sounding opens the door for answering the question: can life exist in Europa&#39;s ice?
On the hemispheric scale, snow on the surface of sea ice significantly impacts the exchange of ma... more On the hemispheric scale, snow on the surface of sea ice significantly impacts the exchange of mass and energy across the ocean-ice-atmosphere interface. The snow cover over Arctic sea ice plays a central role in Arctic photochemistry, including atmospheric depletion events at the onset of spring, and in ecosystem support, by determining the availability of photosynthetically active radiation for algal primary production at the bottom of the ice. Among the non-uniformities of snow relevant to its larger-scale roles is salt content. When snow is deposited on the surface of new sea ice, brine expelled onto the ice surface during ice formation wicks into the snow by capillary action, forming a brine-wetted or saline snow layer at the ice-snow interface. A typical salinity for this basal snow layer in the Arctic (measured on a 3-cm depth interval of melted snow) is about 20 (ppt by optical salinometer), with maxima approaching 30 ppt, thus higher than the salinity of melted surface sea ice (< 12 ppt). Although the physical-chemical properties of this brine-wetted layer have been examined in recent years, and the (assumed) air-derived microbial content of overlying low-salinity snow is known to be low in winter, basal saline snow is essentially unexplored as a microbial habitat. As part of an NSF-supported project on frost flowers, we investigated snow overlying coastal sea ice off Barrow, Alaska, in February 2010 (since snow buries frost flowers). Sterile (ethanol-rinsed) tools were used to open snow pits 60 cm wide, record temperature by thermoprobe at 3-cm depth intervals, and collect samples from newly exposed snow walls for salinity (3-cm intervals) and biological measurements (6-cm intervals). The latter included counts of bacterial abundance by epifluorescence microscopy and assays of extracellular polysaccharide substances (EPS). We also sampled snow on a larger scale to extract sufficient DNA to analyze microbial community composition (ongoing work), as well as underlying sea ice for comparative purposes. Results indicated presence of an areally extensive saline snow layer (salinities of 18.5-30.9 ppt) that was enriched in bacteria (0.28-1.5 x 10E4 bacteria/ml) and EPS (0.07-0.22 mg glucose equivalents/L) relative to overlying low-salinity snow (0.3-9 ppt; 2-9 x 10E2 bacteria/ml; 0.021-0.11 mg glucose equivalents/L). Analysis of content and distribution of salts, bacteria and EPS throughout the snow and underlying sea ice indicated sea-ice brines as the source of these materials in snow. Although marine bacteria appeared to have moved upwards into snow in sync with brine, EPS was subject to different transport or production and degradation pathways, perhaps connected to a detected sensitivity of bacteria in upper sea ice brines to osmotic shock. The possible passive and dynamic roles of bacteria and their exudates in these brine-wetted snows in influencing the physical-chemical properties of snow over sea ice, including later season physical and biological impacts as the snow melts and infiltrates the ice below, await further study.
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