HYDROCARBON BIODEGRADATION AND HYDROCARBONOCLASTIC BACTERIAL COMMUNITIES COMPOSITION GROWN IN SEAWATER AS A FUNCTION OF SODIUM-CHLORIDE CONCENTRATION

Bacterial strains have been enriched and isolated from marine sediment of an oil-contaminated area and grown in a culture medium prepared wi th synthetic seawater (0.4 M NaCl) and containing crude oil (EH1 commu nity) or an hydrocarbon mixture (EH2 community) as sole energy and car bon source. The strains isolated from crude oil were code named EH1 co mmunity; those from the mixture EH2 community. Hydrocarbon biodegradat ion in enrichment culture was maximum for 0.4 M NaCl and decreased for NaCl concentrations above or below this value. However, the effect of NaCl concentration depended somewhat on the nature of the substrate s upplied for growth. With 2 M NaCl, the saturated fraction of crude oil was the only one significantly biodegraded (27%). In contrast, the le vel of biodegradation remains rather high for the standard hydrocarbon mixture: 80-95% for saturated hydrocarbons, 17-34% for aromatics. Few phenotypic differences were noted between strains growing on crude oi l (EH1) and/or mixture of hydrocarbons (EH2). The clustering of the st rains isolated after enrichment at various NaCl concentrations (from 0 to 2 M NaCl) demonstrated the presence of ecotypes of similar bacteri al species. From initial enrichments most of the strains were Gram-neg ative, aerobic rods, possessing few exoenzymes and using mostly fatty acids and organic acids as carbon and energy sources.