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Mercury adaptation among bacteria from
a deep-sea hydrothermal vent
Vetriani et al. 2005
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East Pacific Rise
http://www.mbari.org/molecular/images/EPR%20mussel-map.jpg
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East Pacific RisePhysical properties
First discovered in 1979 Tectonic plates
spreading apart and new crust being formed
Precipitate forms chimney-like constructs
Fluids around 350-360°C (662 – 680°F)
The rise of a plume is a function of water column stratification and the strength of the source
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East Pacific RiseChemical properties
Mercury-rich due to cinnabar (HgS) deposits
Vent fluids rich in metal sulfides mix with oxygen-rich, cold water
Low toxicity, low bioavailability more toxic, more bioavailable
Creates large chemical gradient between vent source and plume http://www.mineralatlas.com/mineral
%20photos/C/
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Ambient seawater vs. vent fluids
Atkins et al. 2002
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East Pacific RiseBiological properties
Vestimentiferans, clams & mussels Harbor symbiotic
chemoautotrophic bacteria Spatially separate acquisition of
oxygen and sulfide Free-living chemoautotrophic
bacteria Thermophiles Mesophiles Psychrophiles
http://bioweb.uwlax.edu/bio203/s2007/rossing_jaco/images/blacksmoker.jpg
http://www.compostinfo.com/images/Tutorial/microbes
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Mercury resistance
First reported in 1960 in Staphylococcus aureus
Unique: only bacterial metal resistance mechanism that transforms its toxic target on a large scale Efflux pumps or extracellular
sequestration most common merA gene
Mercuric reductase Organomercury Hg(II) inert,
monoatomic Hg(0)http://www.sacriver.org/images/mercury/
figure4.jpg
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The study…
Collected vent, plume and control samples from EPR 9° N
Isolated and sequenced using 16S for identification
http://jb.asm.org/content/vol188/issue24/cover.dtl
Alcanivorax
http://genome.jgi-psf.org/pseat/pseat.jpg
http://microbewiki.kenyon.edu/images/6/64/Coccoid
Psychrobacter
Pseudoalteromonas
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The study (cont’d)…
Topt & Hg resistance Various concentrations of HgCl2 in ASW (0 – 75
μM) Plume and vent (mesophilic and thermophilic)
displayed higher Topt & higher Hg resistance than controls
Hg volatilization Add HgCl2 to cultures and add to volatilization
buffer in microplate
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The study (cont’d)…
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The study (cont’d)…
Only four strains were successfully sequenced 1 mesophilic, 3
thermophilic Phylogenetic analysis
revealed a new cluster of merA from thermophilic strains.
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Conclusions
Mesophilic and thermophilic strains from the hydrothermal vent region were resistant to mercury, while control psychrophilic strains were sensitive.
New cluster of merA in thermophilic bacteria
Elevated Topt of MR suggests that this enzyme is of thermophilic origin
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What do you think?
Should they have tested volatilization in more strains? Only used EPR3, 6, 7 and 8
Did they support their hypothesis that thermophilic bacteria are the source of the MR in mesophilic bacteria?
Deep-sea vents origin of life? Evolution of metal resistance in deep-sea
vents? Note to self: How fast does
photodegradation occur in shallow waters?
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References Atkins, M.S., Hanna, M.A., Kupetsky, E.A., Saito, M.A., Taylor, C.D. & Wirsen, C.O.
2002. Tolerance of flagellated protists to high sulfide and metal concentrations potentially encountered at deep-sea hydrothermal vents. Marine Ecology Progress Series. 226:63-75.
Barkay, T., Miller, S.M. & Summers, A.O. 2003. Bacterial mercury resistance from atoms to ecosystems. FEMS Microbiology Reviews. 27:355-384.
German , C.R., Baker, E.T. & Klinkhammer, G. 1995. Regional setting of hydrothermal activity, pp. 3-15. In Parson, L.M., Walker, C.L. & Dixon, D.R. (eds.), Hydrothermal vents and processes. The Geological Society. Geological Society Publishing House, Bath, UK.
Jannasch, H.W. 1995. Microbial interactions with hydrothermal fluids, pp. 273-296. In Humphris, S.E., Zierenberg, R.A., Mullineaux, L.S. & Thomson, R.E. (eds.), Seafloor Hydrothermal Systems; Physical, Chemical, Biological, and Geological Interactions. American Geophysical Union, Washington, DC USA.
Lauro, F.M. & Bartlett, D.H. 2008. Prokaryotic lifestyles in deep-sea habitats. Extremophiles. 12:15-25.
Nakamura, K. & Nakahara, H. 1988. Simplified X-Ray Film Method for Detection of Bacterial Volatilization of Mercury Chloride by Escherichia coli. Applied and Environmental Microbiology. 54(11):2871-2873.
Vetriani, C., Chew, Y.S., Miller, S.M., Yagi, J., Coombs, J., Lutz, R.A. & Barkay, T. 2005. Mercury adaptation among bacteria from a deep-sea hydrothermal vent. Applied and Environmental Microbiology. 71(1):220-226.