Mercury adaptation among bacteria from

a deep-sea hydrothermal vent

Vetriani et al. 2005

East Pacific Rise

http://www.mbari.org/molecular/images/EPR%20mussel-map.jpg

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

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/

Ambient seawater vs. vent fluids

Atkins et al. 2002

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

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

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

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

The study (cont’d)…

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.

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

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?

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.