HR: 0800h
AN: V51C-1501    [Abstracts]
TI: Role of a unique population of lithotrophic, Fe-oxidizing bacteria in forming microbial Fe-mats at the Loihi Seamount.
AU: * Emerson, D
EM: demerson@gmu.edu
AF: American Type Culture Collection, 10801 University Blvd, Manassas, VA 20110 United States
AU: Rentz, J A
EM: jrentz@yahoo.com
AF: American Type Culture Collection, 10801 University Blvd, Manassas, VA 20110 United States
AU: Moyer, C L
EM: cmoyer@hydro.biol.wwu.edu
AF: Western Washington University, Dept of Biology, MS#9160, Bellingham, WA 98225 United States
AB: The Loihi Seamount, located 30 km SE of the island of Hawai'i, is among the most active volcanos on Earth. The summit, at a depth of 1100m, includes a 250m deep caldera (Pele's Pit) formed by an eruption in 1996. The summit, and especially Pele's Pit, are the site of extensive low to intermediate temperature (10° to 65°C) hydrothermal venting, emanating both from diffuse fissures and orifices that have substantial flow rates. The vent fluid is characterized by a low sulfide content, high CO2 concentrations and Fe(II) amounts in the 10s to 100s of æM. Associated with all vents are extensive deposits of iron oxyhydroxides that typically have 107 to 108 bacterial cells/cc associated with them. The morphology of the Fe-oxides are indicative of biological origins. We have isolated microaerophilic, obligately lithotrophic Fe-oxidizing bacteria from Loihi and describe here `Mariprofundus ferroxydans' a unique bacterium that forms a filamentous iron oxide mineral. `M. ferroxydans' is the first cultured representative of a novel division of the Proteobacteria, known previously only from clones from different hydrothermal vent sites. Molecular evidence from Loihi mats based on clone libraries and terminal restriction length polymorphism (T-RFLP) analysis of 16S rRNA genes indicate that this lineage of Fe-oxidizing organisms are common inhabitants at Loihi. We speculate that this organism and its relatives form the basis of an active microbial mat community that owe their existence to the inherent gradients of Fe(II) and O2 that exist at the Loihi vents. In a geological context this is interesting because the Loihi summit and caldera are in an O2-minima zone; O2 concentrations in the bulk seawater are around 0.5 mg/l. In effect, Loihi could serve as a proxy for the late Archaean and early Proterozoic periods when the Earth's atmosphere went from reducing to oxidizing, and it is speculated that abundant Fe(II) in the Earth's oceans served as a major sink for O2 production preventing its accumulation in the atmosphere. Better understanding of extant conditions at Loihi might help us frame questions concerning the role of lithotrophic iron-oxidizing bacteria in the rusty ocean of the late Archaean Earth.
DE: 0410 Biodiversity
DE: 0424 Biosignatures and proxies
DE: 0448 Geomicrobiology
DE: 0450 Hydrothermal systems (1034, 3017, 3616, 4832, 8135, 8424)
DE: 0463 Microbe/mineral interactions
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005