title: Microbial life in a liquid asphalt desert.
abstract: Pitch Lake in Trinidad and Tobago is a natural asphalt reservoir nourished by pitch seepage, a form of petroleum that consists of mostly asphaltines, from the surrounding oil-rich region. During upward seepage, pitch mixes with mud and gases under high pressure, and the lighter portion evaporates or is volatilized, which produces a liquid asphalt residue characterized by low water activity, recalcitrant carbon substrates, and noxious chemical compounds. An active microbial community of archaea and bacteria, many of them novel strains (particularly from the new Tar ARC groups), totaling a biomass of up to 10(7) cells per gram, was found to inhabit the liquid hydrocarbon matrix of Pitch Lake. Geochemical and molecular taxonomic approaches revealed diverse, novel, and deeply branching microbial lineages with the potential to mediate anaerobic hydrocarbon degradation processes in different parts of the asphalt column. In addition, we found markers for archaeal methane metabolism and specific gene sequences affiliated with facultative and obligate anaerobic sulfur- and nitrite-oxidizing bacteria. The microbial diversity at Pitch Lake was found to be unique when compared to microbial communities analyzed at other hydrocarbon-rich environments, which included Rancho Le Brea, a natural asphalt environment in California, USA, and an oil well and a mud volcano in Trinidad and Tobago, among other sites. These results open a window into the microbial ecology and biogeochemistry of recalcitrant hydrocarbon matrices and establish the site as a terrestrial analogue for modeling the biotic potential of hydrocarbon lakes such as those found on Saturn's largest moon Titan.
authors.affiliation: School of Earth and Environmental Sciences, Washington State University, Pullman, 99164-6376, USA. dirksm@wsu.edu
authors.forename: Dirk
authors.initials: D
authors.lastname: Schulze-Makuch
authors.forename: Shirin
authors.initials: S
authors.lastname: Haque
authors.forename: Marina Resendes
authors.initials: MR
authors.lastname: de Sousa Antonio
authors.forename: Denzil
authors.initials: D
authors.lastname: Ali
authors.forename: Riad
authors.initials: R
authors.lastname: Hosein
authors.forename: Young C
authors.initials: YC
authors.lastname: Song
authors.forename: Jinshu
authors.initials: J
authors.lastname: Yang
authors.forename: Elena
authors.initials: E
authors.lastname: Zaikova
authors.forename: Denise M
authors.initials: DM
authors.lastname: Beckles
authors.forename: Edward
authors.initials: E
authors.lastname: Guinan
authors.forename: Harry J
authors.initials: HJ
authors.lastname: Lehto
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Hallam
mesh_terms: D016000:Cluster Analysis; D017753:Ecosystem; D004783:Environmental Microbiology; D019766:Genes, Archaeal; D005798:Genes, Bacterial; D020459:Genes, rRNA; D006838:Hydrocarbons / Q000737:chemistry; D008969:Molecular Sequence Data; D014300:Trinidad and Tobago
chemical_list: D006838:Hydrocarbons; C006647:asphalt