The behaviour of sulphate-reducing microbial community was investigated at the oxic–anoxic interface (0–2 cm) of marine sediments when submitted to oil and enhanced bioturbation activities by the addition of Hediste diversicolor. Although total hydrocarbon removal was not improved by the addition of H. diversicolor, terminal restriction fragment length polymorphism (T-RFLP) analyses based on dsrAB (dissimilatory sulphite reductase) genes and transcripts showed different patterns according to the presence of H. diversicolor which favoured the abundance of dsrB genes during the early stages of incubation. Complementary DNA (cDNA) dsrAB libraries revealed that in presence of H. diversicolor, most dsrAB sequences belonged to hydrocarbonoclastic Desulfobacteraceae, suggesting that sulphate-reducing microorganisms (SRMs) may play an active role in hydrocarbon biodegradation in sediments where the reworking activity is enhanced. Furthermore, the presence of dsrAB sequences related to sequences found associated to environments with high dinitrogen fixation activity suggested potential N2 fixation by SRMs in bioturbated-polluted sediments.