Melitza Crespo-Medina

September 12, 2007

Aerobic Chemosynthesis and Microbial Hg-Resistance at Diffuse Flow Hydrothermal Vents from the

East Pacific Rise at 9ºN

Goals

• To study the abundance and diversity of aerobic chemosynthetic thiosulfate oxidizing bacteria from diffuse flow hydrothermal vents

• To measure the concentration of mercury (Hg) in vent fluids

• To investigate microbially mediated detoxification of heavy metals (such as mercury) by hydrothermal vent bacteria

Diffuse flow fluid sampling:‘04, ‘05 and ‘07

Total Hg (THg) concentration:2.8 to 88.7 ng/L

MPN and bacterial isolation

Direct enrichment

Pure cultures

Sequencing and Identification

Identification of merA gene

MPN with Hgand bacterial

isolation

Methods

Hg detoxification

merR merPmerT merA merB merD

The mer operon:

Mercuric reductase enzyme

Hg2+ Hg0

Vetriani et al., 2005. Appl. Environ. Microbiol. 71: 220-226

() Hg(II) remaining in solution,() OD600 (optical density at 600 nm() Remaining Hg(II) in uninoculated medium

Loss of Hg(II) during growth of strainEPR3

Abundance of chemosynthetic thiosulfate oxidizing bacteria

Pre-eruption Post-eruption

•Total cell counts: 107 to 108 cells/ml

•MPN counts (no Hg): 103 to 107 cells/ml

•MPN counts with Hg: 102 to 104 cells/ml

Gram +

Alphaproteobacteria

Gammaproteobacteria

Phylogenetic analysis of selected thiosulfate oxidizing bacteria isolated form deep-sea vents

Phylogenetic analysis of selected thiosulfate oxidizing bacteria isolated form deep-sea vents

OM

PS

CM

• Gamma proteobacterium

• 95 % similarity to Salinisphaera shabanense

• Isolated in 142-A at 28 ºC

• Facultative autotroph

• Grows in 142+A, ASW, Low strength ASW (0.5 g/l peptone and 0.1 g/L YE)

• Acid producing

• Growth temperature range: 20 - 45 ºC

Optimal growth temp.: 28 - 37 ºC

Conclusion• The abundance of aerobic chemosynthetic thiosulfate oxidizers

ranges from 103 to 107 cells/ml of hydrothermal fluid

• Diffuse flow fluids are enriched with Hg, with concentrations that can be considered toxic to living organisms

• 0.2 to 24.6 % of the chemosynthetic thiosulfate oxidizing organisms are also Hg resistant

• In some cases the abundance of Hg resistant organisms correlates to the THg concentration (e.g., at Tica).

• THg concentration was also measured from focused flow vent fluids and concentrations ranged from 701.3 to 2213.1 ng/L

• Future work include mercury volatilization assays and environmental surveys of merA genes

• Dr. Costantino Vetriani (advisor) and Dr. Tamar Barkay (co-advisor )

• Vetriani and Barkay’s lab members• Dr. John Reinfelder and Derek Wright (Rutgers University)• Nicolas Bloom (Frontier Geoscience)• Dr. George Luther III (University of Delaware)• Dr. Richard Lutz (Rutgers University)• Dr. Timothy Shank (WHOI)• Crew of R/V Atlantis and crew and pilots of the DSV Alvin

Funding:Funding:NIH grant GM58389NIH grant GM58389NSF Graduate Research Fellowship ProgramNSF Graduate Research Fellowship ProgramNSF grant 03-27353 and 04-56676 NSF grant 03-27353 and 04-56676

Acknowledgement