Thesis of Sophie Penet

2004 sept.

" Biodegradation of diesel oil by various environmental and specialized microflorae "
  Sophie Penet supported his thesis on September the 21th. His research was carried out in the “Cloca maxima” team led by Denis Le Paslier (mail) and Abdelghani Sghir (mail) and the French Institut of Petroleum.

  The large use of petroleum products makes them a significant source of pollutants in ground water and soils. Biodegradation studies are therefore relevant either to evaluate possibilities of natural attenuation or define bioremediation strategies. In this study, the possible relationship between the environmental microflorae structures and their capabilities for diesel oil biodegradation was investigated. The degradation capacities, i.e. kinetics and extent of biodegradation, were evaluated in closed batch systems by hydrocarbon consumption and CO2 production, both determined by gas chromatography. The intrinsic biodegradability of different types of diesel oils and the degradation capacities of microflorae from ten polluted and ten unpolluted soils samples were determined. The data showed that: i) diesel oil was biodegradable, ii) n-alkanes were totally degraded by each microflorae, the final amount of residual hydrocarbons being variable, iii) polluted-soil samples exhibited a slightly higher degradation rate (80%) that polluted-soil samples (67%) or activated sludge (64%). In order to define the contribution of various bacterial groups to diesel oil degradation, enrichment cultures were performed on hydrocarbons representative from the structural classes of diesel oil: hexadecane for n-alkanes, pristane for iso-alkanes, decaline for cyclo-alkanes, phrenanthrene for aromatics. By using a 16S rDNA-sequencing method, the bacterial structures of the adapted microflorae were determined and compared to that of the native microflora. A marked effect of the selection pressure was observed on the diversity of the microflorae, each microflora harbouring a major and specific bacterial group. The degradation capacities of the adapted microflorae and the occurrence of genes coding for initial hrydrocarbon oxidation (alkB, nahAc, cypP450) were also studied. No clear relationship between microflorae genes and degradation performances was noted. This seemed to indicate that biodegradation efficiency of soil microflorae depended on the specialized metabolic pathways of some microorganisms and on the cooperation within microbial population.