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Microbial utilization of occurring hydrocarbons by the sediment microbiota of Guaymas basin hydrothermal site (Gulf of California) The Guaymas Basin (Gulf of California) is an actively spreading oceanic basin and a site of hydrothermal activity. The basin floor, at about 2,000 m depth, is covered with a thick layer of pelagic sediments. The thermal alteration of recent sedimentary organic matter by the hydrothermal system generates hydrothermal petroleum. During the French-Mexican cruise Guaynaut, in November 1991, various samples were collected by means of the French submersible Nautile. Among the different scientific objectives of this campaign is the examination of the potential for hydrocarbon degradation by microbiota. Investigations were carried out to characterize hydrocarbons in the collected samples and to research microbial utilization of these hydrocarbons. Degradation of petroleum and one aromatic hydrocarbon (phenanthrene) was observed at 20 degrees C in aerobic conditions for a hydrothermal mineral deposit and some surface sediments. Mesophilic hydrocarbon-utilizing bacterial communities were not capable of growing on hydrocarbons as the sole carbon source. These preliminary results correlate well with geochemical analyses indicating microbial hydrocarbon degradation. The conclusions of this study are in a good agreement with a prior biodegradation study by Bazylinski et al. (1988; 1989) carried out at this hydrothermal site.

In October 16, 1976, the tanker "Bohlen" was wrecked in the Mer d'Iroise, at about 35 miles of Brest, and lossed about 7 000 t of Boscan crude oil. The coast of Brittany was polluted by 3 000 t, and 4000 t were dispersed in the marine environment. In July 1977, 23 surface sediment samples were collected to look for the traces of oil spill in the sea bottom, 9 months after the shipwreck. Only one sediment was very iittle polluted by the Boscan crude oil. Elsewhere, two other kinds of oil pollution were observed in sorne sediment samples. Severa! quantitative and qualitative criteria were used to research sorne oil pollution in the marine sediments and to know the origin: hydrocarbon concentrations, ratios total organic extra ct 1 organic carbon, hydrocarbons 1 organic carbon, quantitative distribution of the 3 fractions of the organic ex tract: saturated hydrocarbons, aromatic hydrocarbons, polar compounds, chromatographie distributions of saturated hydrocarbons, aromatic hydrocarbons and their sulfur compounds (thiophenic compounds). The use of these criteria are discussed in this study., En octobre 1976, le pétrolier« Bohlen »faisait naufrage à 35 miles environ de Brest. Une quantité évaluée à 7 000 t de pétrole brut de Boscan s'échappa du navire; 3 000 t polluèrent le littoral breton et 4 000 t furent dispersées dans le milieu marin. 23 échantillons de sédiment furent prélevés pour rechercher la présence d'une éventuelle pollution par hydrocarbures, 9 mois après le naufrage du pétrolier. Un seul échantillon présentait des signes de pollution très faibles par le brut de Boscan; par ailleurs deux autres types de pollution pétrolière étaient mises en évidence dans certains sédiments .. Les différents critères quantitatifs (analyse pondérale de l'extrait organique et qualitatifs (analyses chromatographiques des hydrocarbures saturés et aromatiques), qui peuvent être utilisés pour déceler une pollution par hydrocarbures dans les sédiments marins et défmir son origine, sont discutés dans cette étude.