Hydrocarbon biodegradation and hydrocarbonoclastic bacterial communities composition grown in seawater as a function of sodium chloride concentration

Abstract

Bacterial strains have been enriched and isolated from marine sediment of an oil-contaminated area and grown in a culture medium prepared with synthetic seawater (0.4 M NaCl) and containing crude oil (EH1 community) or an hydrocarbon mixture (EH2 community) as sole energy and carbon source. The strains isolated from crude oil were code named EH1 community; those from the mixture EH2 community. Hydrocarbon biodegradation 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 supplied for growth. With 2 M NaCl, the saturated fraction of crude oil was the only one significantly biodegraded (27%). In contrast, the level 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 oil (EH1) and/or mixture of hydro-carbons (EH2). The clustering of the strains isolated after enrichment at various NaCl concentrations (from 0 to 2 M NaCl) demonstrated the presence of ecotypes of similar bacterial species. From initial enrichments most of the strains were Gram-negative, aerobic rods, possessing few exoenzymes and using mostly fatty acids and organic acids as carbon and energy sources.