Disentangling oil weathering at a marine seep using GC x GC: broad metabolic specificity accompanies subsurface petroleum biodegradation.

Natural seeps contribute nearly half of the oil entering the coastal ocean. However, environmental fate studies generally monitor fewer than 5% of these petroleum compounds. Hence, the rates and relevance of physical, chemical, and biological weathering processes are unknown for the large majority of hydrocarbons, both released from natural seeps and also from human activities. To investigate the specific compositional changes occurring in petroleum during subsurface degradation and submarine seepage, we studied the natural oil seeps offshore Santa Barbara, California with comprehensive, two-dimensional gas chromatography (GC x GC). With this technique, we quantified changes in the molecular diversity and abundance of hydrocarbons between subsurface reservoirs, a proximal sea floor seep, and the sea surface overlying the seep. We also developed methods to apportion hydrocarbon mass losses due to biodegradation, dissolution, and evaporation, for hundreds of tracked compounds that ascended from the subsurface to the sea floor to the sea surface. The results provide the first quantitative evidence of broad metabolic specificity for anaerobic hydrocarbon degradation in the subsurface and reveal new trends of rapid hydrocarbon evaporation at the sea surface. This study establishes GC x GC as a powerful technique for differentiating biological and physical weathering processes of complex mixtures at a molecular level.

Diversity of Archaea in marine sediments from Skan Bay, Alaska, including cultivated methanogens, and description of Methanogenium boonei sp. nov.

Methanogenesis in cold marine sediments is a globally important process leading to methane hydrate deposits, cold seeps, physical instability of sediment, and atmospheric methane emissions. We employed a multidisciplinary approach that combined culture-dependent and -independent analyses with geochemical measurements in the sediments of Skan Bay, Alaska (53 degrees N, 167 degrees W), to investigate methanogenesis there. Cultivation-independent analyses of the archaeal community revealed that uncultivated microbes of the kingdoms Euryarchaeota and Crenarchaeota are present at Skan Bay and that methanogens constituted a small proportion of the archaeal community. Methanogens were cultivated from depths of 0 to 60 cm in the sediments, and several strains related to the orders Methanomicrobiales and Methanosarcinales were isolated. Isolates were psychrotolerant marine-adapted strains and included an aceticlastic methanogen, strain AK-6, as well as three strains of CO(2)-reducing methanogens: AK-3, AK7, and AK-8. The phylogenetic positions and physiological characteristics of these strains are described. We propose a new species, Methanogenium boonei, with strain AK-7 as the type strain.