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Energetics of chemolithoautotrophy in the hydrothermal system of Vulcano Island, southern Italy
Author(s) -
Amend Jan P.,
Rogers Karyn L.,
Shock Everett L.,
Gurrieri Sergio,
Inguaggiato Salvatore
Publication year - 2003
Publication title -
geobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.859
H-Index - 72
eISSN - 1472-4669
pISSN - 1472-4677
DOI - 10.1046/j.1472-4669.2003.00006.x
Subject(s) - hydrothermal circulation , gibbs free energy , redox , sulfur , chemistry , hydrothermal vent , energetics , yield (engineering) , thermophile , inorganic chemistry , magnetite , nuclear chemistry , mineralogy , geology , materials science , metallurgy , thermodynamics , organic chemistry , physics , seismology , enzyme
The hydrothermal system at Vulcano, Aeolian Islands (Italy), is home to a wide variety of thermophilic, chemolithoautotrophic archaea and bacteria. As observed in laboratory growth studies, these organisms may use an array of terminal electron acceptors (TEAs), including O 2 , , Fe(III), , elemental sulphur and CO 2 ; electron donors include H 2 , , Fe 2+ , H 2 S and CH 4 . Concentrations of inorganic aqueous species and gases were measured in 10 hydrothermal fluids from seeps, wells and vents on Vulcano. These data were combined with standard Gibbs free energies () to calculate overall Gibbs free energies (Δ G r ) of 90 redox reactions that involve 16 inorganic N‐, S‐, C‐, Fe‐, H‐ and O‐bearing compounds. It is shown that oxidation reactions with O 2 as the TEA release significantly more energy (normalized per electron transferred) than most anaerobic oxidation reactions, but the energy yield is comparable or even higher for several reactions in which , or Fe(III) serves as the TEA. For example, the oxidation of CH 4 to CO 2 coupled to the reduction of Fe(III) in magnetite to Fe 2+ releases between 94 and 123 kJ/mol e − , depending on the site. By comparison, the aerobic oxidation of H 2 or reduced inorganic N‐, S‐, C‐ and Fe‐bearing compounds generally yields between 70 and 100 kJ/mol e − . It is further shown that the energy yield from the reduction of elemental sulphur to H 2 S is relatively low (8–19 kJ/mol e − ) despite being a very common metabolism among thermophiles. In addition, for many of the 90 reactions evaluated at each of the 10 sites, values of Δ G r tend to cluster with differences < 20 kJ/mol e − . However, large differences in Δ G r (up to ∼ 60 kJ/mol e − ) are observed in Fe redox reactions, due largely to considerable variations in Fe 2+ , H + and H 2 concentrations. In fact, at the sites investigated, most variations in Δ G r arise from differences in composition and not in temperature.