Dégradation des hydrocarbures et dénitrification bacterienne dans les sédiments marins de la cote mediterranéenne

The bacterial populations located in marine sediments or in the areas of "Etang de Berre" which are regularly polluted by petroleum rejects, are able to degrade hydrocarbons in the presence of ammonium and at a lesser degree in the presence of nitrate as sole nitrogen source. Denitrifying activity was determinated by different methods. The obtained results lead in first approximation to the general following conclusions: - Most of the bacteria which degrade hydrocarbons possess a constitutive nitrate reductase, oxygene and ammonium insensible, which is different from the classical dissimilatory or assimilatory nitrate reductase. - In these bacteria, the lack of nitrite reductase activity allows to explain the nitrite accumulation in the medium where these bacteria grow. Some bacteria linked to phytoplancton have the same characteristics: high nitrate reductase activity, oxygen insensible, and no nitrite reductase activity. - The study of this "constitutive" nitrate reductase produced in aerobic conditions led us to the fact that this enzyme which is similar to the dissimilatory bacterial nitrate reductase behaves in fact as an assimilatory nitrate reductase. - When grown on liquid nutritive medium containine hydrocarbons as sole carbon source and under rigorous shaking, these bacteria can use nitrate in presence or in absence of ammonium. - When fixed on marine sediments used as solid support, these bacterial populations have a denitrifying activity in presence of different carbon sources (amino acids, glucose… but they are unable to de grade hydrocarbons in the presence of nitrate with or without ammonium.